Merge tag 'kvm-ppc-fixes-4.19-2' of git://git.kernel.org/pub/scm/linux/kernel/git...

[linux-2.6-microblaze.git] / kernel / sched / fair.c

// SPDX-License-Identifier: GPL-2.0
/*
 * Completely Fair Scheduling (CFS) Class (SCHED_NORMAL/SCHED_BATCH)
 *
 *  Copyright (C) 2007 Red Hat, Inc., Ingo Molnar <mingo@redhat.com>
 *
 *  Interactivity improvements by Mike Galbraith
 *  (C) 2007 Mike Galbraith <efault@gmx.de>
 *
 *  Various enhancements by Dmitry Adamushko.
 *  (C) 2007 Dmitry Adamushko <dmitry.adamushko@gmail.com>
 *
 *  Group scheduling enhancements by Srivatsa Vaddagiri
 *  Copyright IBM Corporation, 2007
 *  Author: Srivatsa Vaddagiri <vatsa@linux.vnet.ibm.com>
 *
 *  Scaled math optimizations by Thomas Gleixner
 *  Copyright (C) 2007, Thomas Gleixner <tglx@linutronix.de>
 *
 *  Adaptive scheduling granularity, math enhancements by Peter Zijlstra
 *  Copyright (C) 2007 Red Hat, Inc., Peter Zijlstra
 */
#include "sched.h"

#include <trace/events/sched.h>

/*
 * Targeted preemption latency for CPU-bound tasks:
 *
 * NOTE: this latency value is not the same as the concept of
 * 'timeslice length' - timeslices in CFS are of variable length
 * and have no persistent notion like in traditional, time-slice
 * based scheduling concepts.
 *
 * (to see the precise effective timeslice length of your workload,
 *  run vmstat and monitor the context-switches (cs) field)
 *
 * (default: 6ms * (1 + ilog(ncpus)), units: nanoseconds)
 */
unsigned int sysctl_sched_latency                       = 6000000ULL;
unsigned int normalized_sysctl_sched_latency            = 6000000ULL;

/*
 * The initial- and re-scaling of tunables is configurable
 *
 * Options are:
 *
 *   SCHED_TUNABLESCALING_NONE - unscaled, always *1
 *   SCHED_TUNABLESCALING_LOG - scaled logarithmical, *1+ilog(ncpus)
 *   SCHED_TUNABLESCALING_LINEAR - scaled linear, *ncpus
 *
 * (default SCHED_TUNABLESCALING_LOG = *(1+ilog(ncpus))
 */
enum sched_tunable_scaling sysctl_sched_tunable_scaling = SCHED_TUNABLESCALING_LOG;

/*
 * Minimal preemption granularity for CPU-bound tasks:
 *
 * (default: 0.75 msec * (1 + ilog(ncpus)), units: nanoseconds)
 */
unsigned int sysctl_sched_min_granularity               = 750000ULL;
unsigned int normalized_sysctl_sched_min_granularity    = 750000ULL;

/*
 * This value is kept at sysctl_sched_latency/sysctl_sched_min_granularity
 */
static unsigned int sched_nr_latency = 8;

/*
 * After fork, child runs first. If set to 0 (default) then
 * parent will (try to) run first.
 */
unsigned int sysctl_sched_child_runs_first __read_mostly;

/*
 * SCHED_OTHER wake-up granularity.
 *
 * This option delays the preemption effects of decoupled workloads
 * and reduces their over-scheduling. Synchronous workloads will still
 * have immediate wakeup/sleep latencies.
 *
 * (default: 1 msec * (1 + ilog(ncpus)), units: nanoseconds)
 */
unsigned int sysctl_sched_wakeup_granularity            = 1000000UL;
unsigned int normalized_sysctl_sched_wakeup_granularity = 1000000UL;

const_debug unsigned int sysctl_sched_migration_cost    = 500000UL;

#ifdef CONFIG_SMP
/*
 * For asym packing, by default the lower numbered CPU has higher priority.
 */
int __weak arch_asym_cpu_priority(int cpu)
{
        return -cpu;
}
#endif

#ifdef CONFIG_CFS_BANDWIDTH
/*
 * Amount of runtime to allocate from global (tg) to local (per-cfs_rq) pool
 * each time a cfs_rq requests quota.
 *
 * Note: in the case that the slice exceeds the runtime remaining (either due
 * to consumption or the quota being specified to be smaller than the slice)
 * we will always only issue the remaining available time.
 *
 * (default: 5 msec, units: microseconds)
 */
unsigned int sysctl_sched_cfs_bandwidth_slice           = 5000UL;
#endif

/*
 * The margin used when comparing utilization with CPU capacity:
 * util * margin < capacity * 1024
 *
 * (default: ~20%)
 */
unsigned int capacity_margin                            = 1280;

static inline void update_load_add(struct load_weight *lw, unsigned long inc)
{
        lw->weight += inc;
        lw->inv_weight = 0;
}

static inline void update_load_sub(struct load_weight *lw, unsigned long dec)
{
        lw->weight -= dec;
        lw->inv_weight = 0;
}

static inline void update_load_set(struct load_weight *lw, unsigned long w)
{
        lw->weight = w;
        lw->inv_weight = 0;
}

/*
 * Increase the granularity value when there are more CPUs,
 * because with more CPUs the 'effective latency' as visible
 * to users decreases. But the relationship is not linear,
 * so pick a second-best guess by going with the log2 of the
 * number of CPUs.
 *
 * This idea comes from the SD scheduler of Con Kolivas:
 */
static unsigned int get_update_sysctl_factor(void)
{
        unsigned int cpus = min_t(unsigned int, num_online_cpus(), 8);
        unsigned int factor;

        switch (sysctl_sched_tunable_scaling) {
        case SCHED_TUNABLESCALING_NONE:
                factor = 1;
                break;
        case SCHED_TUNABLESCALING_LINEAR:
                factor = cpus;
                break;
        case SCHED_TUNABLESCALING_LOG:
        default:
                factor = 1 + ilog2(cpus);
                break;
        }

        return factor;
}

static void update_sysctl(void)
{
        unsigned int factor = get_update_sysctl_factor();

#define SET_SYSCTL(name) \
        (sysctl_##name = (factor) * normalized_sysctl_##name)
        SET_SYSCTL(sched_min_granularity);
        SET_SYSCTL(sched_latency);
        SET_SYSCTL(sched_wakeup_granularity);
#undef SET_SYSCTL
}

void sched_init_granularity(void)
{
        update_sysctl();
}

#define WMULT_CONST     (~0U)
#define WMULT_SHIFT     32

static void __update_inv_weight(struct load_weight *lw)
{
        unsigned long w;

        if (likely(lw->inv_weight))
                return;

        w = scale_load_down(lw->weight);

        if (BITS_PER_LONG > 32 && unlikely(w >= WMULT_CONST))
                lw->inv_weight = 1;
        else if (unlikely(!w))
                lw->inv_weight = WMULT_CONST;
        else
                lw->inv_weight = WMULT_CONST / w;
}

/*
 * delta_exec * weight / lw.weight
 *   OR
 * (delta_exec * (weight * lw->inv_weight)) >> WMULT_SHIFT
 *
 * Either weight := NICE_0_LOAD and lw \e sched_prio_to_wmult[], in which case
 * we're guaranteed shift stays positive because inv_weight is guaranteed to
 * fit 32 bits, and NICE_0_LOAD gives another 10 bits; therefore shift >= 22.
 *
 * Or, weight =< lw.weight (because lw.weight is the runqueue weight), thus
 * weight/lw.weight <= 1, and therefore our shift will also be positive.
 */
static u64 __calc_delta(u64 delta_exec, unsigned long weight, struct load_weight *lw)
{
        u64 fact = scale_load_down(weight);
        int shift = WMULT_SHIFT;

        __update_inv_weight(lw);

        if (unlikely(fact >> 32)) {
                while (fact >> 32) {
                        fact >>= 1;
                        shift--;
                }
        }

        /* hint to use a 32x32->64 mul */
        fact = (u64)(u32)fact * lw->inv_weight;

        while (fact >> 32) {
                fact >>= 1;
                shift--;
        }

        return mul_u64_u32_shr(delta_exec, fact, shift);
}


const struct sched_class fair_sched_class;

/**************************************************************
 * CFS operations on generic schedulable entities:
 */

#ifdef CONFIG_FAIR_GROUP_SCHED

/* cpu runqueue to which this cfs_rq is attached */
static inline struct rq *rq_of(struct cfs_rq *cfs_rq)
{
        return cfs_rq->rq;
}

static inline struct task_struct *task_of(struct sched_entity *se)
{
        SCHED_WARN_ON(!entity_is_task(se));
        return container_of(se, struct task_struct, se);
}

/* Walk up scheduling entities hierarchy */
#define for_each_sched_entity(se) \
                for (; se; se = se->parent)

static inline struct cfs_rq *task_cfs_rq(struct task_struct *p)
{
        return p->se.cfs_rq;
}

/* runqueue on which this entity is (to be) queued */
static inline struct cfs_rq *cfs_rq_of(struct sched_entity *se)
{
        return se->cfs_rq;
}

/* runqueue "owned" by this group */
static inline struct cfs_rq *group_cfs_rq(struct sched_entity *grp)
{
        return grp->my_q;
}

static inline void list_add_leaf_cfs_rq(struct cfs_rq *cfs_rq)
{
        if (!cfs_rq->on_list) {
                struct rq *rq = rq_of(cfs_rq);
                int cpu = cpu_of(rq);
                /*
                 * Ensure we either appear before our parent (if already
                 * enqueued) or force our parent to appear after us when it is
                 * enqueued. The fact that we always enqueue bottom-up
                 * reduces this to two cases and a special case for the root
                 * cfs_rq. Furthermore, it also means that we will always reset
                 * tmp_alone_branch either when the branch is connected
                 * to a tree or when we reach the beg of the tree
                 */
                if (cfs_rq->tg->parent &&
                    cfs_rq->tg->parent->cfs_rq[cpu]->on_list) {
                        /*
                         * If parent is already on the list, we add the child
                         * just before. Thanks to circular linked property of
                         * the list, this means to put the child at the tail
                         * of the list that starts by parent.
                         */
                        list_add_tail_rcu(&cfs_rq->leaf_cfs_rq_list,
                                &(cfs_rq->tg->parent->cfs_rq[cpu]->leaf_cfs_rq_list));
                        /*
                         * The branch is now connected to its tree so we can
                         * reset tmp_alone_branch to the beginning of the
                         * list.
                         */
                        rq->tmp_alone_branch = &rq->leaf_cfs_rq_list;
                } else if (!cfs_rq->tg->parent) {
                        /*
                         * cfs rq without parent should be put
                         * at the tail of the list.
                         */
                        list_add_tail_rcu(&cfs_rq->leaf_cfs_rq_list,
                                &rq->leaf_cfs_rq_list);
                        /*
                         * We have reach the beg of a tree so we can reset
                         * tmp_alone_branch to the beginning of the list.
                         */
                        rq->tmp_alone_branch = &rq->leaf_cfs_rq_list;
                } else {
                        /*
                         * The parent has not already been added so we want to
                         * make sure that it will be put after us.
                         * tmp_alone_branch points to the beg of the branch
                         * where we will add parent.
                         */
                        list_add_rcu(&cfs_rq->leaf_cfs_rq_list,
                                rq->tmp_alone_branch);
                        /*
                         * update tmp_alone_branch to points to the new beg
                         * of the branch
                         */
                        rq->tmp_alone_branch = &cfs_rq->leaf_cfs_rq_list;
                }

                cfs_rq->on_list = 1;
        }
}

static inline void list_del_leaf_cfs_rq(struct cfs_rq *cfs_rq)
{
        if (cfs_rq->on_list) {
                list_del_rcu(&cfs_rq->leaf_cfs_rq_list);
                cfs_rq->on_list = 0;
        }
}

/* Iterate thr' all leaf cfs_rq's on a runqueue */
#define for_each_leaf_cfs_rq_safe(rq, cfs_rq, pos)                      \
        list_for_each_entry_safe(cfs_rq, pos, &rq->leaf_cfs_rq_list,    \
                                 leaf_cfs_rq_list)

/* Do the two (enqueued) entities belong to the same group ? */
static inline struct cfs_rq *
is_same_group(struct sched_entity *se, struct sched_entity *pse)
{
        if (se->cfs_rq == pse->cfs_rq)
                return se->cfs_rq;

        return NULL;
}

static inline struct sched_entity *parent_entity(struct sched_entity *se)
{
        return se->parent;
}

static void
find_matching_se(struct sched_entity **se, struct sched_entity **pse)
{
        int se_depth, pse_depth;

        /*
         * preemption test can be made between sibling entities who are in the
         * same cfs_rq i.e who have a common parent. Walk up the hierarchy of
         * both tasks until we find their ancestors who are siblings of common
         * parent.
         */

        /* First walk up until both entities are at same depth */
        se_depth = (*se)->depth;
        pse_depth = (*pse)->depth;

        while (se_depth > pse_depth) {
                se_depth--;
                *se = parent_entity(*se);
        }

        while (pse_depth > se_depth) {
                pse_depth--;
                *pse = parent_entity(*pse);
        }

        while (!is_same_group(*se, *pse)) {
                *se = parent_entity(*se);
                *pse = parent_entity(*pse);
        }
}

#else   /* !CONFIG_FAIR_GROUP_SCHED */

static inline struct task_struct *task_of(struct sched_entity *se)
{
        return container_of(se, struct task_struct, se);
}

static inline struct rq *rq_of(struct cfs_rq *cfs_rq)
{
        return container_of(cfs_rq, struct rq, cfs);
}


#define for_each_sched_entity(se) \
                for (; se; se = NULL)

static inline struct cfs_rq *task_cfs_rq(struct task_struct *p)
{
        return &task_rq(p)->cfs;
}

static inline struct cfs_rq *cfs_rq_of(struct sched_entity *se)
{
        struct task_struct *p = task_of(se);
        struct rq *rq = task_rq(p);

        return &rq->cfs;
}

/* runqueue "owned" by this group */
static inline struct cfs_rq *group_cfs_rq(struct sched_entity *grp)
{
        return NULL;
}

static inline void list_add_leaf_cfs_rq(struct cfs_rq *cfs_rq)
{
}

static inline void list_del_leaf_cfs_rq(struct cfs_rq *cfs_rq)
{
}

#define for_each_leaf_cfs_rq_safe(rq, cfs_rq, pos)      \
                for (cfs_rq = &rq->cfs, pos = NULL; cfs_rq; cfs_rq = pos)

static inline struct sched_entity *parent_entity(struct sched_entity *se)
{
        return NULL;
}

static inline void
find_matching_se(struct sched_entity **se, struct sched_entity **pse)
{
}

#endif  /* CONFIG_FAIR_GROUP_SCHED */

static __always_inline
void account_cfs_rq_runtime(struct cfs_rq *cfs_rq, u64 delta_exec);

/**************************************************************
 * Scheduling class tree data structure manipulation methods:
 */

static inline u64 max_vruntime(u64 max_vruntime, u64 vruntime)
{
        s64 delta = (s64)(vruntime - max_vruntime);
        if (delta > 0)
                max_vruntime = vruntime;

        return max_vruntime;
}

static inline u64 min_vruntime(u64 min_vruntime, u64 vruntime)
{
        s64 delta = (s64)(vruntime - min_vruntime);
        if (delta < 0)
                min_vruntime = vruntime;

        return min_vruntime;
}

static inline int entity_before(struct sched_entity *a,
                                struct sched_entity *b)
{
        return (s64)(a->vruntime - b->vruntime) < 0;
}

static void update_min_vruntime(struct cfs_rq *cfs_rq)
{
        struct sched_entity *curr = cfs_rq->curr;
        struct rb_node *leftmost = rb_first_cached(&cfs_rq->tasks_timeline);

        u64 vruntime = cfs_rq->min_vruntime;

        if (curr) {
                if (curr->on_rq)
                        vruntime = curr->vruntime;
                else
                        curr = NULL;
        }

        if (leftmost) { /* non-empty tree */
                struct sched_entity *se;
                se = rb_entry(leftmost, struct sched_entity, run_node);

                if (!curr)
                        vruntime = se->vruntime;
                else
                        vruntime = min_vruntime(vruntime, se->vruntime);
        }

        /* ensure we never gain time by being placed backwards. */
        cfs_rq->min_vruntime = max_vruntime(cfs_rq->min_vruntime, vruntime);
#ifndef CONFIG_64BIT
        smp_wmb();
        cfs_rq->min_vruntime_copy = cfs_rq->min_vruntime;
#endif
}

/*
 * Enqueue an entity into the rb-tree:
 */
static void __enqueue_entity(struct cfs_rq *cfs_rq, struct sched_entity *se)
{
        struct rb_node **link = &cfs_rq->tasks_timeline.rb_root.rb_node;
        struct rb_node *parent = NULL;
        struct sched_entity *entry;
        bool leftmost = true;

        /*
         * Find the right place in the rbtree:
         */
        while (*link) {
                parent = *link;
                entry = rb_entry(parent, struct sched_entity, run_node);
                /*
                 * We dont care about collisions. Nodes with
                 * the same key stay together.
                 */
                if (entity_before(se, entry)) {
                        link = &parent->rb_left;
                } else {
                        link = &parent->rb_right;
                        leftmost = false;
                }
        }

        rb_link_node(&se->run_node, parent, link);
        rb_insert_color_cached(&se->run_node,
                               &cfs_rq->tasks_timeline, leftmost);
}

static void __dequeue_entity(struct cfs_rq *cfs_rq, struct sched_entity *se)
{
        rb_erase_cached(&se->run_node, &cfs_rq->tasks_timeline);
}

struct sched_entity *__pick_first_entity(struct cfs_rq *cfs_rq)
{
        struct rb_node *left = rb_first_cached(&cfs_rq->tasks_timeline);

        if (!left)
                return NULL;

        return rb_entry(left, struct sched_entity, run_node);
}

static struct sched_entity *__pick_next_entity(struct sched_entity *se)
{
        struct rb_node *next = rb_next(&se->run_node);

        if (!next)
                return NULL;

        return rb_entry(next, struct sched_entity, run_node);
}

#ifdef CONFIG_SCHED_DEBUG
struct sched_entity *__pick_last_entity(struct cfs_rq *cfs_rq)
{
        struct rb_node *last = rb_last(&cfs_rq->tasks_timeline.rb_root);

        if (!last)
                return NULL;

        return rb_entry(last, struct sched_entity, run_node);
}

/**************************************************************
 * Scheduling class statistics methods:
 */

int sched_proc_update_handler(struct ctl_table *table, int write,
                void __user *buffer, size_t *lenp,
                loff_t *ppos)
{
        int ret = proc_dointvec_minmax(table, write, buffer, lenp, ppos);
        unsigned int factor = get_update_sysctl_factor();

        if (ret || !write)
                return ret;

        sched_nr_latency = DIV_ROUND_UP(sysctl_sched_latency,
                                        sysctl_sched_min_granularity);

#define WRT_SYSCTL(name) \
        (normalized_sysctl_##name = sysctl_##name / (factor))
        WRT_SYSCTL(sched_min_granularity);
        WRT_SYSCTL(sched_latency);
        WRT_SYSCTL(sched_wakeup_granularity);
#undef WRT_SYSCTL

        return 0;
}
#endif

/*
 * delta /= w
 */
static inline u64 calc_delta_fair(u64 delta, struct sched_entity *se)
{
        if (unlikely(se->load.weight != NICE_0_LOAD))
                delta = __calc_delta(delta, NICE_0_LOAD, &se->load);

        return delta;
}

/*
 * The idea is to set a period in which each task runs once.
 *
 * When there are too many tasks (sched_nr_latency) we have to stretch
 * this period because otherwise the slices get too small.
 *
 * p = (nr <= nl) ? l : l*nr/nl
 */
static u64 __sched_period(unsigned long nr_running)
{
        if (unlikely(nr_running > sched_nr_latency))
                return nr_running * sysctl_sched_min_granularity;
        else
                return sysctl_sched_latency;
}

/*
 * We calculate the wall-time slice from the period by taking a part
 * proportional to the weight.
 *
 * s = p*P[w/rw]
 */
static u64 sched_slice(struct cfs_rq *cfs_rq, struct sched_entity *se)
{
        u64 slice = __sched_period(cfs_rq->nr_running + !se->on_rq);

        for_each_sched_entity(se) {
                struct load_weight *load;
                struct load_weight lw;

                cfs_rq = cfs_rq_of(se);
                load = &cfs_rq->load;

                if (unlikely(!se->on_rq)) {
                        lw = cfs_rq->load;

                        update_load_add(&lw, se->load.weight);
                        load = &lw;
                }
                slice = __calc_delta(slice, se->load.weight, load);
        }
        return slice;
}

/*
 * We calculate the vruntime slice of a to-be-inserted task.
 *
 * vs = s/w
 */
static u64 sched_vslice(struct cfs_rq *cfs_rq, struct sched_entity *se)
{
        return calc_delta_fair(sched_slice(cfs_rq, se), se);
}

#ifdef CONFIG_SMP
#include "pelt.h"
#include "sched-pelt.h"

static int select_idle_sibling(struct task_struct *p, int prev_cpu, int cpu);
static unsigned long task_h_load(struct task_struct *p);

/* Give new sched_entity start runnable values to heavy its load in infant time */
void init_entity_runnable_average(struct sched_entity *se)
{
        struct sched_avg *sa = &se->avg;

        memset(sa, 0, sizeof(*sa));

        /*
         * Tasks are intialized with full load to be seen as heavy tasks until
         * they get a chance to stabilize to their real load level.
         * Group entities are intialized with zero load to reflect the fact that
         * nothing has been attached to the task group yet.
         */
        if (entity_is_task(se))
                sa->runnable_load_avg = sa->load_avg = scale_load_down(se->load.weight);

        se->runnable_weight = se->load.weight;

        /* when this task enqueue'ed, it will contribute to its cfs_rq's load_avg */
}

static inline u64 cfs_rq_clock_task(struct cfs_rq *cfs_rq);
static void attach_entity_cfs_rq(struct sched_entity *se);

/*
 * With new tasks being created, their initial util_avgs are extrapolated
 * based on the cfs_rq's current util_avg:
 *
 *   util_avg = cfs_rq->util_avg / (cfs_rq->load_avg + 1) * se.load.weight
 *
 * However, in many cases, the above util_avg does not give a desired
 * value. Moreover, the sum of the util_avgs may be divergent, such
 * as when the series is a harmonic series.
 *
 * To solve this problem, we also cap the util_avg of successive tasks to
 * only 1/2 of the left utilization budget:
 *
 *   util_avg_cap = (cpu_scale - cfs_rq->avg.util_avg) / 2^n
 *
 * where n denotes the nth task and cpu_scale the CPU capacity.
 *
 * For example, for a CPU with 1024 of capacity, a simplest series from
 * the beginning would be like:
 *
 *  task  util_avg: 512, 256, 128,  64,  32,   16,    8, ...
 * cfs_rq util_avg: 512, 768, 896, 960, 992, 1008, 1016, ...
 *
 * Finally, that extrapolated util_avg is clamped to the cap (util_avg_cap)
 * if util_avg > util_avg_cap.
 */
void post_init_entity_util_avg(struct sched_entity *se)
{
        struct cfs_rq *cfs_rq = cfs_rq_of(se);
        struct sched_avg *sa = &se->avg;
        long cpu_scale = arch_scale_cpu_capacity(NULL, cpu_of(rq_of(cfs_rq)));
        long cap = (long)(cpu_scale - cfs_rq->avg.util_avg) / 2;

        if (cap > 0) {
                if (cfs_rq->avg.util_avg != 0) {
                        sa->util_avg  = cfs_rq->avg.util_avg * se->load.weight;
                        sa->util_avg /= (cfs_rq->avg.load_avg + 1);

                        if (sa->util_avg > cap)
                                sa->util_avg = cap;
                } else {
                        sa->util_avg = cap;
                }
        }

        if (entity_is_task(se)) {
                struct task_struct *p = task_of(se);
                if (p->sched_class != &fair_sched_class) {
                        /*
                         * For !fair tasks do:
                         *
                        update_cfs_rq_load_avg(now, cfs_rq);
                        attach_entity_load_avg(cfs_rq, se, 0);
                        switched_from_fair(rq, p);
                         *
                         * such that the next switched_to_fair() has the
                         * expected state.
                         */
                        se->avg.last_update_time = cfs_rq_clock_task(cfs_rq);
                        return;
                }
        }

        attach_entity_cfs_rq(se);
}

#else /* !CONFIG_SMP */
void init_entity_runnable_average(struct sched_entity *se)
{
}
void post_init_entity_util_avg(struct sched_entity *se)
{
}
static void update_tg_load_avg(struct cfs_rq *cfs_rq, int force)
{
}
#endif /* CONFIG_SMP */

/*
 * Update the current task's runtime statistics.
 */
static void update_curr(struct cfs_rq *cfs_rq)
{
        struct sched_entity *curr = cfs_rq->curr;
        u64 now = rq_clock_task(rq_of(cfs_rq));
        u64 delta_exec;

        if (unlikely(!curr))
                return;

        delta_exec = now - curr->exec_start;
        if (unlikely((s64)delta_exec <= 0))
                return;

        curr->exec_start = now;

        schedstat_set(curr->statistics.exec_max,
                      max(delta_exec, curr->statistics.exec_max));

        curr->sum_exec_runtime += delta_exec;
        schedstat_add(cfs_rq->exec_clock, delta_exec);

        curr->vruntime += calc_delta_fair(delta_exec, curr);
        update_min_vruntime(cfs_rq);

        if (entity_is_task(curr)) {
                struct task_struct *curtask = task_of(curr);

                trace_sched_stat_runtime(curtask, delta_exec, curr->vruntime);
                cgroup_account_cputime(curtask, delta_exec);
                account_group_exec_runtime(curtask, delta_exec);
        }

        account_cfs_rq_runtime(cfs_rq, delta_exec);
}

static void update_curr_fair(struct rq *rq)
{
        update_curr(cfs_rq_of(&rq->curr->se));
}

static inline void
update_stats_wait_start(struct cfs_rq *cfs_rq, struct sched_entity *se)
{
        u64 wait_start, prev_wait_start;

        if (!schedstat_enabled())
                return;

        wait_start = rq_clock(rq_of(cfs_rq));
        prev_wait_start = schedstat_val(se->statistics.wait_start);

        if (entity_is_task(se) && task_on_rq_migrating(task_of(se)) &&
            likely(wait_start > prev_wait_start))
                wait_start -= prev_wait_start;

        __schedstat_set(se->statistics.wait_start, wait_start);
}

static inline void
update_stats_wait_end(struct cfs_rq *cfs_rq, struct sched_entity *se)
{
        struct task_struct *p;
        u64 delta;

        if (!schedstat_enabled())
                return;

        delta = rq_clock(rq_of(cfs_rq)) - schedstat_val(se->statistics.wait_start);

        if (entity_is_task(se)) {
                p = task_of(se);
                if (task_on_rq_migrating(p)) {
                        /*
                         * Preserve migrating task's wait time so wait_start
                         * time stamp can be adjusted to accumulate wait time
                         * prior to migration.
                         */
                        __schedstat_set(se->statistics.wait_start, delta);
                        return;
                }
                trace_sched_stat_wait(p, delta);
        }

        __schedstat_set(se->statistics.wait_max,
                      max(schedstat_val(se->statistics.wait_max), delta));
        __schedstat_inc(se->statistics.wait_count);
        __schedstat_add(se->statistics.wait_sum, delta);
        __schedstat_set(se->statistics.wait_start, 0);
}

static inline void
update_stats_enqueue_sleeper(struct cfs_rq *cfs_rq, struct sched_entity *se)
{
        struct task_struct *tsk = NULL;
        u64 sleep_start, block_start;

        if (!schedstat_enabled())
                return;

        sleep_start = schedstat_val(se->statistics.sleep_start);
        block_start = schedstat_val(se->statistics.block_start);

        if (entity_is_task(se))
                tsk = task_of(se);

        if (sleep_start) {
                u64 delta = rq_clock(rq_of(cfs_rq)) - sleep_start;

                if ((s64)delta < 0)
                        delta = 0;

                if (unlikely(delta > schedstat_val(se->statistics.sleep_max)))
                        __schedstat_set(se->statistics.sleep_max, delta);

                __schedstat_set(se->statistics.sleep_start, 0);
                __schedstat_add(se->statistics.sum_sleep_runtime, delta);

                if (tsk) {
                        account_scheduler_latency(tsk, delta >> 10, 1);
                        trace_sched_stat_sleep(tsk, delta);
                }
        }
        if (block_start) {
                u64 delta = rq_clock(rq_of(cfs_rq)) - block_start;

                if ((s64)delta < 0)
                        delta = 0;

                if (unlikely(delta > schedstat_val(se->statistics.block_max)))
                        __schedstat_set(se->statistics.block_max, delta);

                __schedstat_set(se->statistics.block_start, 0);
                __schedstat_add(se->statistics.sum_sleep_runtime, delta);

                if (tsk) {
                        if (tsk->in_iowait) {
                                __schedstat_add(se->statistics.iowait_sum, delta);
                                __schedstat_inc(se->statistics.iowait_count);
                                trace_sched_stat_iowait(tsk, delta);
                        }

                        trace_sched_stat_blocked(tsk, delta);

                        /*
                         * Blocking time is in units of nanosecs, so shift by
                         * 20 to get a milliseconds-range estimation of the
                         * amount of time that the task spent sleeping:
                         */
                        if (unlikely(prof_on == SLEEP_PROFILING)) {
                                profile_hits(SLEEP_PROFILING,
                                                (void *)get_wchan(tsk),
                                                delta >> 20);
                        }
                        account_scheduler_latency(tsk, delta >> 10, 0);
                }
        }
}

/*
 * Task is being enqueued - update stats:
 */
static inline void
update_stats_enqueue(struct cfs_rq *cfs_rq, struct sched_entity *se, int flags)
{
        if (!schedstat_enabled())
                return;

        /*
         * Are we enqueueing a waiting task? (for current tasks
         * a dequeue/enqueue event is a NOP)
         */
        if (se != cfs_rq->curr)
                update_stats_wait_start(cfs_rq, se);

        if (flags & ENQUEUE_WAKEUP)
                update_stats_enqueue_sleeper(cfs_rq, se);
}

static inline void
update_stats_dequeue(struct cfs_rq *cfs_rq, struct sched_entity *se, int flags)
{

        if (!schedstat_enabled())
                return;

        /*
         * Mark the end of the wait period if dequeueing a
         * waiting task:
         */
        if (se != cfs_rq->curr)
                update_stats_wait_end(cfs_rq, se);

        if ((flags & DEQUEUE_SLEEP) && entity_is_task(se)) {
                struct task_struct *tsk = task_of(se);

                if (tsk->state & TASK_INTERRUPTIBLE)
                        __schedstat_set(se->statistics.sleep_start,
                                      rq_clock(rq_of(cfs_rq)));
                if (tsk->state & TASK_UNINTERRUPTIBLE)
                        __schedstat_set(se->statistics.block_start,
                                      rq_clock(rq_of(cfs_rq)));
        }
}

/*
 * We are picking a new current task - update its stats:
 */
static inline void
update_stats_curr_start(struct cfs_rq *cfs_rq, struct sched_entity *se)
{
        /*
         * We are starting a new run period:
         */
        se->exec_start = rq_clock_task(rq_of(cfs_rq));
}

/**************************************************
 * Scheduling class queueing methods:
 */

#ifdef CONFIG_NUMA_BALANCING
/*
 * Approximate time to scan a full NUMA task in ms. The task scan period is
 * calculated based on the tasks virtual memory size and
 * numa_balancing_scan_size.
 */
unsigned int sysctl_numa_balancing_scan_period_min = 1000;
unsigned int sysctl_numa_balancing_scan_period_max = 60000;

/* Portion of address space to scan in MB */
unsigned int sysctl_numa_balancing_scan_size = 256;

/* Scan @scan_size MB every @scan_period after an initial @scan_delay in ms */
unsigned int sysctl_numa_balancing_scan_delay = 1000;

struct numa_group {
        atomic_t refcount;

        spinlock_t lock; /* nr_tasks, tasks */
        int nr_tasks;
        pid_t gid;
        int active_nodes;

        struct rcu_head rcu;
        unsigned long total_faults;
        unsigned long max_faults_cpu;
        /*
         * Faults_cpu is used to decide whether memory should move
         * towards the CPU. As a consequence, these stats are weighted
         * more by CPU use than by memory faults.
         */
        unsigned long *faults_cpu;
        unsigned long faults[0];
};

static inline unsigned long group_faults_priv(struct numa_group *ng);
static inline unsigned long group_faults_shared(struct numa_group *ng);

static unsigned int task_nr_scan_windows(struct task_struct *p)
{
        unsigned long rss = 0;
        unsigned long nr_scan_pages;

        /*
         * Calculations based on RSS as non-present and empty pages are skipped
         * by the PTE scanner and NUMA hinting faults should be trapped based
         * on resident pages
         */
        nr_scan_pages = sysctl_numa_balancing_scan_size << (20 - PAGE_SHIFT);
        rss = get_mm_rss(p->mm);
        if (!rss)
                rss = nr_scan_pages;

        rss = round_up(rss, nr_scan_pages);
        return rss / nr_scan_pages;
}

/* For sanitys sake, never scan more PTEs than MAX_SCAN_WINDOW MB/sec. */
#define MAX_SCAN_WINDOW 2560

static unsigned int task_scan_min(struct task_struct *p)
{
        unsigned int scan_size = READ_ONCE(sysctl_numa_balancing_scan_size);
        unsigned int scan, floor;
        unsigned int windows = 1;

        if (scan_size < MAX_SCAN_WINDOW)
                windows = MAX_SCAN_WINDOW / scan_size;
        floor = 1000 / windows;

        scan = sysctl_numa_balancing_scan_period_min / task_nr_scan_windows(p);
        return max_t(unsigned int, floor, scan);
}

static unsigned int task_scan_start(struct task_struct *p)
{
        unsigned long smin = task_scan_min(p);
        unsigned long period = smin;

        /* Scale the maximum scan period with the amount of shared memory. */
        if (p->numa_group) {
                struct numa_group *ng = p->numa_group;
                unsigned long shared = group_faults_shared(ng);
                unsigned long private = group_faults_priv(ng);

                period *= atomic_read(&ng->refcount);
                period *= shared + 1;
                period /= private + shared + 1;
        }

        return max(smin, period);
}

static unsigned int task_scan_max(struct task_struct *p)
{
        unsigned long smin = task_scan_min(p);
        unsigned long smax;

        /* Watch for min being lower than max due to floor calculations */
        smax = sysctl_numa_balancing_scan_period_max / task_nr_scan_windows(p);

        /* Scale the maximum scan period with the amount of shared memory. */
        if (p->numa_group) {
                struct numa_group *ng = p->numa_group;
                unsigned long shared = group_faults_shared(ng);
                unsigned long private = group_faults_priv(ng);
                unsigned long period = smax;

                period *= atomic_read(&ng->refcount);
                period *= shared + 1;
                period /= private + shared + 1;

                smax = max(smax, period);
        }

        return max(smin, smax);
}

void init_numa_balancing(unsigned long clone_flags, struct task_struct *p)
{
        int mm_users = 0;
        struct mm_struct *mm = p->mm;

        if (mm) {
                mm_users = atomic_read(&mm->mm_users);
                if (mm_users == 1) {
                        mm->numa_next_scan = jiffies + msecs_to_jiffies(sysctl_numa_balancing_scan_delay);
                        mm->numa_scan_seq = 0;
                }
        }
        p->node_stamp                   = 0;
        p->numa_scan_seq                = mm ? mm->numa_scan_seq : 0;
        p->numa_scan_period             = sysctl_numa_balancing_scan_delay;
        p->numa_work.next               = &p->numa_work;
        p->numa_faults                  = NULL;
        p->numa_group                   = NULL;
        p->last_task_numa_placement     = 0;
        p->last_sum_exec_runtime        = 0;

        /* New address space, reset the preferred nid */
        if (!(clone_flags & CLONE_VM)) {
                p->numa_preferred_nid = -1;
                return;
        }

        /*
         * New thread, keep existing numa_preferred_nid which should be copied
         * already by arch_dup_task_struct but stagger when scans start.
         */
        if (mm) {
                unsigned int delay;

                delay = min_t(unsigned int, task_scan_max(current),
                        current->numa_scan_period * mm_users * NSEC_PER_MSEC);
                delay += 2 * TICK_NSEC;
                p->node_stamp = delay;
        }
}

static void account_numa_enqueue(struct rq *rq, struct task_struct *p)
{
        rq->nr_numa_running += (p->numa_preferred_nid != -1);
        rq->nr_preferred_running += (p->numa_preferred_nid == task_node(p));
}

static void account_numa_dequeue(struct rq *rq, struct task_struct *p)
{
        rq->nr_numa_running -= (p->numa_preferred_nid != -1);
        rq->nr_preferred_running -= (p->numa_preferred_nid == task_node(p));
}

/* Shared or private faults. */
#define NR_NUMA_HINT_FAULT_TYPES 2

/* Memory and CPU locality */
#define NR_NUMA_HINT_FAULT_STATS (NR_NUMA_HINT_FAULT_TYPES * 2)

/* Averaged statistics, and temporary buffers. */
#define NR_NUMA_HINT_FAULT_BUCKETS (NR_NUMA_HINT_FAULT_STATS * 2)

pid_t task_numa_group_id(struct task_struct *p)
{
        return p->numa_group ? p->numa_group->gid : 0;
}

/*
 * The averaged statistics, shared & private, memory & CPU,
 * occupy the first half of the array. The second half of the
 * array is for current counters, which are averaged into the
 * first set by task_numa_placement.
 */
static inline int task_faults_idx(enum numa_faults_stats s, int nid, int priv)
{
        return NR_NUMA_HINT_FAULT_TYPES * (s * nr_node_ids + nid) + priv;
}

static inline unsigned long task_faults(struct task_struct *p, int nid)
{
        if (!p->numa_faults)
                return 0;

        return p->numa_faults[task_faults_idx(NUMA_MEM, nid, 0)] +
                p->numa_faults[task_faults_idx(NUMA_MEM, nid, 1)];
}

static inline unsigned long group_faults(struct task_struct *p, int nid)
{
        if (!p->numa_group)
                return 0;

        return p->numa_group->faults[task_faults_idx(NUMA_MEM, nid, 0)] +
                p->numa_group->faults[task_faults_idx(NUMA_MEM, nid, 1)];
}

static inline unsigned long group_faults_cpu(struct numa_group *group, int nid)
{
        return group->faults_cpu[task_faults_idx(NUMA_MEM, nid, 0)] +
                group->faults_cpu[task_faults_idx(NUMA_MEM, nid, 1)];
}

static inline unsigned long group_faults_priv(struct numa_group *ng)
{
        unsigned long faults = 0;
        int node;

        for_each_online_node(node) {
                faults += ng->faults[task_faults_idx(NUMA_MEM, node, 1)];
        }

        return faults;
}

static inline unsigned long group_faults_shared(struct numa_group *ng)
{
        unsigned long faults = 0;
        int node;

        for_each_online_node(node) {
                faults += ng->faults[task_faults_idx(NUMA_MEM, node, 0)];
        }

        return faults;
}

/*
 * A node triggering more than 1/3 as many NUMA faults as the maximum is
 * considered part of a numa group's pseudo-interleaving set. Migrations
 * between these nodes are slowed down, to allow things to settle down.
 */
#define ACTIVE_NODE_FRACTION 3

static bool numa_is_active_node(int nid, struct numa_group *ng)
{
        return group_faults_cpu(ng, nid) * ACTIVE_NODE_FRACTION > ng->max_faults_cpu;
}

/* Handle placement on systems where not all nodes are directly connected. */
static unsigned long score_nearby_nodes(struct task_struct *p, int nid,
                                        int maxdist, bool task)
{
        unsigned long score = 0;
        int node;

        /*
         * All nodes are directly connected, and the same distance
         * from each other. No need for fancy placement algorithms.
         */
        if (sched_numa_topology_type == NUMA_DIRECT)
                return 0;

        /*
         * This code is called for each node, introducing N^2 complexity,
         * which should be ok given the number of nodes rarely exceeds 8.
         */
        for_each_online_node(node) {
                unsigned long faults;
                int dist = node_distance(nid, node);

                /*
                 * The furthest away nodes in the system are not interesting
                 * for placement; nid was already counted.
                 */
                if (dist == sched_max_numa_distance || node == nid)
                        continue;

                /*
                 * On systems with a backplane NUMA topology, compare groups
                 * of nodes, and move tasks towards the group with the most
                 * memory accesses. When comparing two nodes at distance
                 * "hoplimit", only nodes closer by than "hoplimit" are part
                 * of each group. Skip other nodes.
                 */
                if (sched_numa_topology_type == NUMA_BACKPLANE &&
                                        dist >= maxdist)
                        continue;

                /* Add up the faults from nearby nodes. */
                if (task)
                        faults = task_faults(p, node);
                else
                        faults = group_faults(p, node);

                /*
                 * On systems with a glueless mesh NUMA topology, there are
                 * no fixed "groups of nodes". Instead, nodes that are not
                 * directly connected bounce traffic through intermediate
                 * nodes; a numa_group can occupy any set of nodes.
                 * The further away a node is, the less the faults count.
                 * This seems to result in good task placement.
                 */
                if (sched_numa_topology_type == NUMA_GLUELESS_MESH) {
                        faults *= (sched_max_numa_distance - dist);
                        faults /= (sched_max_numa_distance - LOCAL_DISTANCE);
                }

                score += faults;
        }

        return score;
}

/*
 * These return the fraction of accesses done by a particular task, or
 * task group, on a particular numa node.  The group weight is given a
 * larger multiplier, in order to group tasks together that are almost
 * evenly spread out between numa nodes.
 */
static inline unsigned long task_weight(struct task_struct *p, int nid,
                                        int dist)
{
        unsigned long faults, total_faults;

        if (!p->numa_faults)
                return 0;

        total_faults = p->total_numa_faults;

        if (!total_faults)
                return 0;

        faults = task_faults(p, nid);
        faults += score_nearby_nodes(p, nid, dist, true);

        return 1000 * faults / total_faults;
}

static inline unsigned long group_weight(struct task_struct *p, int nid,
                                         int dist)
{
        unsigned long faults, total_faults;

        if (!p->numa_group)
                return 0;

        total_faults = p->numa_group->total_faults;

        if (!total_faults)
                return 0;

        faults = group_faults(p, nid);
        faults += score_nearby_nodes(p, nid, dist, false);

        return 1000 * faults / total_faults;
}

bool should_numa_migrate_memory(struct task_struct *p, struct page * page,
                                int src_nid, int dst_cpu)
{
        struct numa_group *ng = p->numa_group;
        int dst_nid = cpu_to_node(dst_cpu);
        int last_cpupid, this_cpupid;

        this_cpupid = cpu_pid_to_cpupid(dst_cpu, current->pid);

        /*
         * Multi-stage node selection is used in conjunction with a periodic
         * migration fault to build a temporal task<->page relation. By using
         * a two-stage filter we remove short/unlikely relations.
         *
         * Using P(p) ~ n_p / n_t as per frequentist probability, we can equate
         * a task's usage of a particular page (n_p) per total usage of this
         * page (n_t) (in a given time-span) to a probability.
         *
         * Our periodic faults will sample this probability and getting the
         * same result twice in a row, given these samples are fully
         * independent, is then given by P(n)^2, provided our sample period
         * is sufficiently short compared to the usage pattern.
         *
         * This quadric squishes small probabilities, making it less likely we
         * act on an unlikely task<->page relation.
         */
        last_cpupid = page_cpupid_xchg_last(page, this_cpupid);
        if (!cpupid_pid_unset(last_cpupid) &&
                                cpupid_to_nid(last_cpupid) != dst_nid)
                return false;

        /* Always allow migrate on private faults */
        if (cpupid_match_pid(p, last_cpupid))
                return true;

        /* A shared fault, but p->numa_group has not been set up yet. */
        if (!ng)
                return true;

        /*
         * Destination node is much more heavily used than the source
         * node? Allow migration.
         */
        if (group_faults_cpu(ng, dst_nid) > group_faults_cpu(ng, src_nid) *
                                        ACTIVE_NODE_FRACTION)
                return true;

        /*
         * Distribute memory according to CPU & memory use on each node,
         * with 3/4 hysteresis to avoid unnecessary memory migrations:
         *
         * faults_cpu(dst)   3   faults_cpu(src)
         * --------------- * - > ---------------
         * faults_mem(dst)   4   faults_mem(src)
         */
        return group_faults_cpu(ng, dst_nid) * group_faults(p, src_nid) * 3 >
               group_faults_cpu(ng, src_nid) * group_faults(p, dst_nid) * 4;
}

static unsigned long weighted_cpuload(struct rq *rq);
static unsigned long source_load(int cpu, int type);
static unsigned long target_load(int cpu, int type);
static unsigned long capacity_of(int cpu);

/* Cached statistics for all CPUs within a node */
struct numa_stats {
        unsigned long load;

        /* Total compute capacity of CPUs on a node */
        unsigned long compute_capacity;

        unsigned int nr_running;
};

/*
 * XXX borrowed from update_sg_lb_stats
 */
static void update_numa_stats(struct numa_stats *ns, int nid)
{
        int smt, cpu, cpus = 0;
        unsigned long capacity;

        memset(ns, 0, sizeof(*ns));
        for_each_cpu(cpu, cpumask_of_node(nid)) {
                struct rq *rq = cpu_rq(cpu);

                ns->nr_running += rq->nr_running;
                ns->load += weighted_cpuload(rq);
                ns->compute_capacity += capacity_of(cpu);

                cpus++;
        }

        /*
         * If we raced with hotplug and there are no CPUs left in our mask
         * the @ns structure is NULL'ed and task_numa_compare() will
         * not find this node attractive.
         *
         * We'll detect a huge imbalance and bail there.
         */
        if (!cpus)
                return;

        /* smt := ceil(cpus / capacity), assumes: 1 < smt_power < 2 */
        smt = DIV_ROUND_UP(SCHED_CAPACITY_SCALE * cpus, ns->compute_capacity);
        capacity = cpus / smt; /* cores */

        capacity = min_t(unsigned, capacity,
                DIV_ROUND_CLOSEST(ns->compute_capacity, SCHED_CAPACITY_SCALE));
}

struct task_numa_env {
        struct task_struct *p;

        int src_cpu, src_nid;
        int dst_cpu, dst_nid;

        struct numa_stats src_stats, dst_stats;

        int imbalance_pct;
        int dist;

        struct task_struct *best_task;
        long best_imp;
        int best_cpu;
};

static void task_numa_assign(struct task_numa_env *env,
                             struct task_struct *p, long imp)
{
        if (env->best_task)
                put_task_struct(env->best_task);
        if (p)
                get_task_struct(p);

        env->best_task = p;
        env->best_imp = imp;
        env->best_cpu = env->dst_cpu;
}

static bool load_too_imbalanced(long src_load, long dst_load,
                                struct task_numa_env *env)
{
        long imb, old_imb;
        long orig_src_load, orig_dst_load;
        long src_capacity, dst_capacity;

        /*
         * The load is corrected for the CPU capacity available on each node.
         *
         * src_load        dst_load
         * ------------ vs ---------
         * src_capacity    dst_capacity
         */
        src_capacity = env->src_stats.compute_capacity;
        dst_capacity = env->dst_stats.compute_capacity;

        imb = abs(dst_load * src_capacity - src_load * dst_capacity);

        orig_src_load = env->src_stats.load;
        orig_dst_load = env->dst_stats.load;

        old_imb = abs(orig_dst_load * src_capacity - orig_src_load * dst_capacity);

        /* Would this change make things worse? */
        return (imb > old_imb);
}

/*
 * This checks if the overall compute and NUMA accesses of the system would
 * be improved if the source tasks was migrated to the target dst_cpu taking
 * into account that it might be best if task running on the dst_cpu should
 * be exchanged with the source task
 */
static void task_numa_compare(struct task_numa_env *env,
                              long taskimp, long groupimp, bool maymove)
{
        struct rq *dst_rq = cpu_rq(env->dst_cpu);
        struct task_struct *cur;
        long src_load, dst_load;
        long load;
        long imp = env->p->numa_group ? groupimp : taskimp;
        long moveimp = imp;
        int dist = env->dist;

        rcu_read_lock();
        cur = task_rcu_dereference(&dst_rq->curr);
        if (cur && ((cur->flags & PF_EXITING) || is_idle_task(cur)))
                cur = NULL;

        /*
         * Because we have preemption enabled we can get migrated around and
         * end try selecting ourselves (current == env->p) as a swap candidate.
         */
        if (cur == env->p)
                goto unlock;

        if (!cur) {
                if (maymove || imp > env->best_imp)
                        goto assign;
                else
                        goto unlock;
        }

        /*
         * "imp" is the fault differential for the source task between the
         * source and destination node. Calculate the total differential for
         * the source task and potential destination task. The more negative
         * the value is, the more remote accesses that would be expected to
         * be incurred if the tasks were swapped.
         */
        /* Skip this swap candidate if cannot move to the source cpu */
        if (!cpumask_test_cpu(env->src_cpu, &cur->cpus_allowed))
                goto unlock;

        /*
         * If dst and source tasks are in the same NUMA group, or not
         * in any group then look only at task weights.
         */
        if (cur->numa_group == env->p->numa_group) {
                imp = taskimp + task_weight(cur, env->src_nid, dist) -
                      task_weight(cur, env->dst_nid, dist);
                /*
                 * Add some hysteresis to prevent swapping the
                 * tasks within a group over tiny differences.
                 */
                if (cur->numa_group)
                        imp -= imp / 16;
        } else {
                /*
                 * Compare the group weights. If a task is all by itself
                 * (not part of a group), use the task weight instead.
                 */
                if (cur->numa_group && env->p->numa_group)
                        imp += group_weight(cur, env->src_nid, dist) -
                               group_weight(cur, env->dst_nid, dist);
                else
                        imp += task_weight(cur, env->src_nid, dist) -
                               task_weight(cur, env->dst_nid, dist);
        }

        if (imp <= env->best_imp)
                goto unlock;

        if (maymove && moveimp > imp && moveimp > env->best_imp) {
                imp = moveimp - 1;
                cur = NULL;
                goto assign;
        }

        /*
         * In the overloaded case, try and keep the load balanced.
         */
        load = task_h_load(env->p) - task_h_load(cur);
        if (!load)
                goto assign;

        dst_load = env->dst_stats.load + load;
        src_load = env->src_stats.load - load;

        if (load_too_imbalanced(src_load, dst_load, env))
                goto unlock;

assign:
        /*
         * One idle CPU per node is evaluated for a task numa move.
         * Call select_idle_sibling to maybe find a better one.
         */
        if (!cur) {
                /*
                 * select_idle_siblings() uses an per-CPU cpumask that
                 * can be used from IRQ context.
                 */
                local_irq_disable();
                env->dst_cpu = select_idle_sibling(env->p, env->src_cpu,
                                                   env->dst_cpu);
                local_irq_enable();
        }

        task_numa_assign(env, cur, imp);
unlock:
        rcu_read_unlock();
}

static void task_numa_find_cpu(struct task_numa_env *env,
                                long taskimp, long groupimp)
{
        long src_load, dst_load, load;
        bool maymove = false;
        int cpu;

        load = task_h_load(env->p);
        dst_load = env->dst_stats.load + load;
        src_load = env->src_stats.load - load;

        /*
         * If the improvement from just moving env->p direction is better
         * than swapping tasks around, check if a move is possible.
         */
        maymove = !load_too_imbalanced(src_load, dst_load, env);

        for_each_cpu(cpu, cpumask_of_node(env->dst_nid)) {
                /* Skip this CPU if the source task cannot migrate */
                if (!cpumask_test_cpu(cpu, &env->p->cpus_allowed))
                        continue;

                env->dst_cpu = cpu;
                task_numa_compare(env, taskimp, groupimp, maymove);
        }
}

static int task_numa_migrate(struct task_struct *p)
{
        struct task_numa_env env = {
                .p = p,

                .src_cpu = task_cpu(p),
                .src_nid = task_node(p),

                .imbalance_pct = 112,

                .best_task = NULL,
                .best_imp = 0,
                .best_cpu = -1,
        };
        struct sched_domain *sd;
        unsigned long taskweight, groupweight;
        int nid, ret, dist;
        long taskimp, groupimp;

        /*
         * Pick the lowest SD_NUMA domain, as that would have the smallest
         * imbalance and would be the first to start moving tasks about.
         *
         * And we want to avoid any moving of tasks about, as that would create
         * random movement of tasks -- counter the numa conditions we're trying
         * to satisfy here.
         */
        rcu_read_lock();
        sd = rcu_dereference(per_cpu(sd_numa, env.src_cpu));
        if (sd)
                env.imbalance_pct = 100 + (sd->imbalance_pct - 100) / 2;
        rcu_read_unlock();

        /*
         * Cpusets can break the scheduler domain tree into smaller
         * balance domains, some of which do not cross NUMA boundaries.
         * Tasks that are "trapped" in such domains cannot be migrated
         * elsewhere, so there is no point in (re)trying.
         */
        if (unlikely(!sd)) {
                sched_setnuma(p, task_node(p));
                return -EINVAL;
        }

        env.dst_nid = p->numa_preferred_nid;
        dist = env.dist = node_distance(env.src_nid, env.dst_nid);
        taskweight = task_weight(p, env.src_nid, dist);
        groupweight = group_weight(p, env.src_nid, dist);
        update_numa_stats(&env.src_stats, env.src_nid);
        taskimp = task_weight(p, env.dst_nid, dist) - taskweight;
        groupimp = group_weight(p, env.dst_nid, dist) - groupweight;
        update_numa_stats(&env.dst_stats, env.dst_nid);

        /* Try to find a spot on the preferred nid. */
        task_numa_find_cpu(&env, taskimp, groupimp);

        /*
         * Look at other nodes in these cases:
         * - there is no space available on the preferred_nid
         * - the task is part of a numa_group that is interleaved across
         *   multiple NUMA nodes; in order to better consolidate the group,
         *   we need to check other locations.
         */
        if (env.best_cpu == -1 || (p->numa_group && p->numa_group->active_nodes > 1)) {
                for_each_online_node(nid) {
                        if (nid == env.src_nid || nid == p->numa_preferred_nid)
                                continue;

                        dist = node_distance(env.src_nid, env.dst_nid);
                        if (sched_numa_topology_type == NUMA_BACKPLANE &&
                                                dist != env.dist) {
                                taskweight = task_weight(p, env.src_nid, dist);
                                groupweight = group_weight(p, env.src_nid, dist);
                        }

                        /* Only consider nodes where both task and groups benefit */
                        taskimp = task_weight(p, nid, dist) - taskweight;
                        groupimp = group_weight(p, nid, dist) - groupweight;
                        if (taskimp < 0 && groupimp < 0)
                                continue;

                        env.dist = dist;
                        env.dst_nid = nid;
                        update_numa_stats(&env.dst_stats, env.dst_nid);
                        task_numa_find_cpu(&env, taskimp, groupimp);
                }
        }

        /*
         * If the task is part of a workload that spans multiple NUMA nodes,
         * and is migrating into one of the workload's active nodes, remember
         * this node as the task's preferred numa node, so the workload can
         * settle down.
         * A task that migrated to a second choice node will be better off
         * trying for a better one later. Do not set the preferred node here.
         */
        if (p->numa_group) {
                if (env.best_cpu == -1)
                        nid = env.src_nid;
                else
                        nid = cpu_to_node(env.best_cpu);

                if (nid != p->numa_preferred_nid)
                        sched_setnuma(p, nid);
        }

        /* No better CPU than the current one was found. */
        if (env.best_cpu == -1)
                return -EAGAIN;

        /*
         * Reset the scan period if the task is being rescheduled on an
         * alternative node to recheck if the tasks is now properly placed.
         */
        p->numa_scan_period = task_scan_start(p);

        if (env.best_task == NULL) {
                ret = migrate_task_to(p, env.best_cpu);
                if (ret != 0)
                        trace_sched_stick_numa(p, env.src_cpu, env.best_cpu);
                return ret;
        }

        ret = migrate_swap(p, env.best_task, env.best_cpu, env.src_cpu);

        if (ret != 0)
                trace_sched_stick_numa(p, env.src_cpu, task_cpu(env.best_task));
        put_task_struct(env.best_task);
        return ret;
}

/* Attempt to migrate a task to a CPU on the preferred node. */
static void numa_migrate_preferred(struct task_struct *p)
{
        unsigned long interval = HZ;

        /* This task has no NUMA fault statistics yet */
        if (unlikely(p->numa_preferred_nid == -1 || !p->numa_faults))
                return;

        /* Periodically retry migrating the task to the preferred node */
        interval = min(interval, msecs_to_jiffies(p->numa_scan_period) / 16);
        p->numa_migrate_retry = jiffies + interval;

        /* Success if task is already running on preferred CPU */
        if (task_node(p) == p->numa_preferred_nid)
                return;

        /* Otherwise, try migrate to a CPU on the preferred node */
        task_numa_migrate(p);
}

/*
 * Find out how many nodes on the workload is actively running on. Do this by
 * tracking the nodes from which NUMA hinting faults are triggered. This can
 * be different from the set of nodes where the workload's memory is currently
 * located.
 */
static void numa_group_count_active_nodes(struct numa_group *numa_group)
{
        unsigned long faults, max_faults = 0;
        int nid, active_nodes = 0;

        for_each_online_node(nid) {
                faults = group_faults_cpu(numa_group, nid);
                if (faults > max_faults)
                        max_faults = faults;
        }

        for_each_online_node(nid) {
                faults = group_faults_cpu(numa_group, nid);
                if (faults * ACTIVE_NODE_FRACTION > max_faults)
                        active_nodes++;
        }

        numa_group->max_faults_cpu = max_faults;
        numa_group->active_nodes = active_nodes;
}

/*
 * When adapting the scan rate, the period is divided into NUMA_PERIOD_SLOTS
 * increments. The more local the fault statistics are, the higher the scan
 * period will be for the next scan window. If local/(local+remote) ratio is
 * below NUMA_PERIOD_THRESHOLD (where range of ratio is 1..NUMA_PERIOD_SLOTS)
 * the scan period will decrease. Aim for 70% local accesses.
 */
#define NUMA_PERIOD_SLOTS 10
#define NUMA_PERIOD_THRESHOLD 7

/*
 * Increase the scan period (slow down scanning) if the majority of
 * our memory is already on our local node, or if the majority of
 * the page accesses are shared with other processes.
 * Otherwise, decrease the scan period.
 */
static void update_task_scan_period(struct task_struct *p,
                        unsigned long shared, unsigned long private)
{
        unsigned int period_slot;
        int lr_ratio, ps_ratio;
        int diff;

        unsigned long remote = p->numa_faults_locality[0];
        unsigned long local = p->numa_faults_locality[1];

        /*
         * If there were no record hinting faults then either the task is
         * completely idle or all activity is areas that are not of interest
         * to automatic numa balancing. Related to that, if there were failed
         * migration then it implies we are migrating too quickly or the local
         * node is overloaded. In either case, scan slower
         */
        if (local + shared == 0 || p->numa_faults_locality[2]) {
                p->numa_scan_period = min(p->numa_scan_period_max,
                        p->numa_scan_period << 1);

                p->mm->numa_next_scan = jiffies +
                        msecs_to_jiffies(p->numa_scan_period);

                return;
        }

        /*
         * Prepare to scale scan period relative to the current period.
         *       == NUMA_PERIOD_THRESHOLD scan period stays the same
         *       <  NUMA_PERIOD_THRESHOLD scan period decreases (scan faster)
         *       >= NUMA_PERIOD_THRESHOLD scan period increases (scan slower)
         */
        period_slot = DIV_ROUND_UP(p->numa_scan_period, NUMA_PERIOD_SLOTS);
        lr_ratio = (local * NUMA_PERIOD_SLOTS) / (local + remote);
        ps_ratio = (private * NUMA_PERIOD_SLOTS) / (private + shared);

        if (ps_ratio >= NUMA_PERIOD_THRESHOLD) {
                /*
                 * Most memory accesses are local. There is no need to
                 * do fast NUMA scanning, since memory is already local.
                 */
                int slot = ps_ratio - NUMA_PERIOD_THRESHOLD;
                if (!slot)
                        slot = 1;
                diff = slot * period_slot;
        } else if (lr_ratio >= NUMA_PERIOD_THRESHOLD) {
                /*
                 * Most memory accesses are shared with other tasks.
                 * There is no point in continuing fast NUMA scanning,
                 * since other tasks may just move the memory elsewhere.
                 */
                int slot = lr_ratio - NUMA_PERIOD_THRESHOLD;
                if (!slot)
                        slot = 1;
                diff = slot * period_slot;
        } else {
                /*
                 * Private memory faults exceed (SLOTS-THRESHOLD)/SLOTS,
                 * yet they are not on the local NUMA node. Speed up
                 * NUMA scanning to get the memory moved over.
                 */
                int ratio = max(lr_ratio, ps_ratio);
                diff = -(NUMA_PERIOD_THRESHOLD - ratio) * period_slot;
        }

        p->numa_scan_period = clamp(p->numa_scan_period + diff,
                        task_scan_min(p), task_scan_max(p));
        memset(p->numa_faults_locality, 0, sizeof(p->numa_faults_locality));
}

/*
 * Get the fraction of time the task has been running since the last
 * NUMA placement cycle. The scheduler keeps similar statistics, but
 * decays those on a 32ms period, which is orders of magnitude off
 * from the dozens-of-seconds NUMA balancing period. Use the scheduler
 * stats only if the task is so new there are no NUMA statistics yet.
 */
static u64 numa_get_avg_runtime(struct task_struct *p, u64 *period)
{
        u64 runtime, delta, now;
        /* Use the start of this time slice to avoid calculations. */
        now = p->se.exec_start;
        runtime = p->se.sum_exec_runtime;

        if (p->last_task_numa_placement) {
                delta = runtime - p->last_sum_exec_runtime;
                *period = now - p->last_task_numa_placement;
        } else {
                delta = p->se.avg.load_sum;
                *period = LOAD_AVG_MAX;
        }

        p->last_sum_exec_runtime = runtime;
        p->last_task_numa_placement = now;

        return delta;
}

/*
 * Determine the preferred nid for a task in a numa_group. This needs to
 * be done in a way that produces consistent results with group_weight,
 * otherwise workloads might not converge.
 */
static int preferred_group_nid(struct task_struct *p, int nid)
{
        nodemask_t nodes;
        int dist;

        /* Direct connections between all NUMA nodes. */
        if (sched_numa_topology_type == NUMA_DIRECT)
                return nid;

        /*
         * On a system with glueless mesh NUMA topology, group_weight
         * scores nodes according to the number of NUMA hinting faults on
         * both the node itself, and on nearby nodes.
         */
        if (sched_numa_topology_type == NUMA_GLUELESS_MESH) {
                unsigned long score, max_score = 0;
                int node, max_node = nid;

                dist = sched_max_numa_distance;

                for_each_online_node(node) {
                        score = group_weight(p, node, dist);
                        if (score > max_score) {
                                max_score = score;
                                max_node = node;
                        }
                }
                return max_node;
        }

        /*
         * Finding the preferred nid in a system with NUMA backplane
         * interconnect topology is more involved. The goal is to locate
         * tasks from numa_groups near each other in the system, and
         * untangle workloads from different sides of the system. This requires
         * searching down the hierarchy of node groups, recursively searching
         * inside the highest scoring group of nodes. The nodemask tricks
         * keep the complexity of the search down.
         */
        nodes = node_online_map;
        for (dist = sched_max_numa_distance; dist > LOCAL_DISTANCE; dist--) {
                unsigned long max_faults = 0;
                nodemask_t max_group = NODE_MASK_NONE;
                int a, b;

                /* Are there nodes at this distance from each other? */
                if (!find_numa_distance(dist))
                        continue;

                for_each_node_mask(a, nodes) {
                        unsigned long faults = 0;
                        nodemask_t this_group;
                        nodes_clear(this_group);

                        /* Sum group's NUMA faults; includes a==b case. */
                        for_each_node_mask(b, nodes) {
                                if (node_distance(a, b) < dist) {
                                        faults += group_faults(p, b);
                                        node_set(b, this_group);
                                        node_clear(b, nodes);
                                }
                        }

                        /* Remember the top group. */
                        if (faults > max_faults) {
                                max_faults = faults;
                                max_group = this_group;
                                /*
                                 * subtle: at the smallest distance there is
                                 * just one node left in each "group", the
                                 * winner is the preferred nid.
                                 */
                                nid = a;
                        }
                }
                /* Next round, evaluate the nodes within max_group. */
                if (!max_faults)
                        break;
                nodes = max_group;
        }
        return nid;
}

static void task_numa_placement(struct task_struct *p)
{
        int seq, nid, max_nid = -1;
        unsigned long max_faults = 0;
        unsigned long fault_types[2] = { 0, 0 };
        unsigned long total_faults;
        u64 runtime, period;
        spinlock_t *group_lock = NULL;

        /*
         * The p->mm->numa_scan_seq field gets updated without
         * exclusive access. Use READ_ONCE() here to ensure
         * that the field is read in a single access:
         */
        seq = READ_ONCE(p->mm->numa_scan_seq);
        if (p->numa_scan_seq == seq)
                return;
        p->numa_scan_seq = seq;
        p->numa_scan_period_max = task_scan_max(p);

        total_faults = p->numa_faults_locality[0] +
                       p->numa_faults_locality[1];
        runtime = numa_get_avg_runtime(p, &period);

        /* If the task is part of a group prevent parallel updates to group stats */
        if (p->numa_group) {
                group_lock = &p->numa_group->lock;
                spin_lock_irq(group_lock);
        }

        /* Find the node with the highest number of faults */
        for_each_online_node(nid) {
                /* Keep track of the offsets in numa_faults array */
                int mem_idx, membuf_idx, cpu_idx, cpubuf_idx;
                unsigned long faults = 0, group_faults = 0;
                int priv;

                for (priv = 0; priv < NR_NUMA_HINT_FAULT_TYPES; priv++) {
                        long diff, f_diff, f_weight;

                        mem_idx = task_faults_idx(NUMA_MEM, nid, priv);
                        membuf_idx = task_faults_idx(NUMA_MEMBUF, nid, priv);
                        cpu_idx = task_faults_idx(NUMA_CPU, nid, priv);
                        cpubuf_idx = task_faults_idx(NUMA_CPUBUF, nid, priv);

                        /* Decay existing window, copy faults since last scan */
                        diff = p->numa_faults[membuf_idx] - p->numa_faults[mem_idx] / 2;
                        fault_types[priv] += p->numa_faults[membuf_idx];
                        p->numa_faults[membuf_idx] = 0;

                        /*
                         * Normalize the faults_from, so all tasks in a group
                         * count according to CPU use, instead of by the raw
                         * number of faults. Tasks with little runtime have
                         * little over-all impact on throughput, and thus their
                         * faults are less important.
                         */
                        f_weight = div64_u64(runtime << 16, period + 1);
                        f_weight = (f_weight * p->numa_faults[cpubuf_idx]) /
                                   (total_faults + 1);
                        f_diff = f_weight - p->numa_faults[cpu_idx] / 2;
                        p->numa_faults[cpubuf_idx] = 0;

                        p->numa_faults[mem_idx] += diff;
                        p->numa_faults[cpu_idx] += f_diff;
                        faults += p->numa_faults[mem_idx];
                        p->total_numa_faults += diff;
                        if (p->numa_group) {
                                /*
                                 * safe because we can only change our own group
                                 *
                                 * mem_idx represents the offset for a given
                                 * nid and priv in a specific region because it
                                 * is at the beginning of the numa_faults array.
                                 */
                                p->numa_group->faults[mem_idx] += diff;
                                p->numa_group->faults_cpu[mem_idx] += f_diff;
                                p->numa_group->total_faults += diff;
                                group_faults += p->numa_group->faults[mem_idx];
                        }
                }

                if (!p->numa_group) {
                        if (faults > max_faults) {
                                max_faults = faults;
                                max_nid = nid;
                        }
                } else if (group_faults > max_faults) {
                        max_faults = group_faults;
                        max_nid = nid;
                }
        }

        if (p->numa_group) {
                numa_group_count_active_nodes(p->numa_group);
                spin_unlock_irq(group_lock);
                max_nid = preferred_group_nid(p, max_nid);
        }

        if (max_faults) {
                /* Set the new preferred node */
                if (max_nid != p->numa_preferred_nid)
                        sched_setnuma(p, max_nid);
        }

        update_task_scan_period(p, fault_types[0], fault_types[1]);
}

static inline int get_numa_group(struct numa_group *grp)
{
        return atomic_inc_not_zero(&grp->refcount);
}

static inline void put_numa_group(struct numa_group *grp)
{
        if (atomic_dec_and_test(&grp->refcount))
                kfree_rcu(grp, rcu);
}

static void task_numa_group(struct task_struct *p, int cpupid, int flags,
                        int *priv)
{
        struct numa_group *grp, *my_grp;
        struct task_struct *tsk;
        bool join = false;
        int cpu = cpupid_to_cpu(cpupid);
        int i;

        if (unlikely(!p->numa_group)) {
                unsigned int size = sizeof(struct numa_group) +
                                    4*nr_node_ids*sizeof(unsigned long);

                grp = kzalloc(size, GFP_KERNEL | __GFP_NOWARN);
                if (!grp)
                        return;

                atomic_set(&grp->refcount, 1);
                grp->active_nodes = 1;
                grp->max_faults_cpu = 0;
                spin_lock_init(&grp->lock);
                grp->gid = p->pid;
                /* Second half of the array tracks nids where faults happen */
                grp->faults_cpu = grp->faults + NR_NUMA_HINT_FAULT_TYPES *
                                                nr_node_ids;

                for (i = 0; i < NR_NUMA_HINT_FAULT_STATS * nr_node_ids; i++)
                        grp->faults[i] = p->numa_faults[i];

                grp->total_faults = p->total_numa_faults;

                grp->nr_tasks++;
                rcu_assign_pointer(p->numa_group, grp);
        }

        rcu_read_lock();
        tsk = READ_ONCE(cpu_rq(cpu)->curr);

        if (!cpupid_match_pid(tsk, cpupid))
                goto no_join;

        grp = rcu_dereference(tsk->numa_group);
        if (!grp)
                goto no_join;

        my_grp = p->numa_group;
        if (grp == my_grp)
                goto no_join;

        /*
         * Only join the other group if its bigger; if we're the bigger group,
         * the other task will join us.
         */
        if (my_grp->nr_tasks > grp->nr_tasks)
                goto no_join;

        /*
         * Tie-break on the grp address.
         */
        if (my_grp->nr_tasks == grp->nr_tasks && my_grp > grp)
                goto no_join;

        /* Always join threads in the same process. */
        if (tsk->mm == current->mm)
                join = true;

        /* Simple filter to avoid false positives due to PID collisions */
        if (flags & TNF_SHARED)
                join = true;

        /* Update priv based on whether false sharing was detected */
        *priv = !join;

        if (join && !get_numa_group(grp))
                goto no_join;

        rcu_read_unlock();

        if (!join)
                return;

        BUG_ON(irqs_disabled());
        double_lock_irq(&my_grp->lock, &grp->lock);

        for (i = 0; i < NR_NUMA_HINT_FAULT_STATS * nr_node_ids; i++) {
                my_grp->faults[i] -= p->numa_faults[i];
                grp->faults[i] += p->numa_faults[i];
        }
        my_grp->total_faults -= p->total_numa_faults;
        grp->total_faults += p->total_numa_faults;

        my_grp->nr_tasks--;
        grp->nr_tasks++;

        spin_unlock(&my_grp->lock);
        spin_unlock_irq(&grp->lock);

        rcu_assign_pointer(p->numa_group, grp);

        put_numa_group(my_grp);
        return;

no_join:
        rcu_read_unlock();
        return;
}

void task_numa_free(struct task_struct *p)
{
        struct numa_group *grp = p->numa_group;
        void *numa_faults = p->numa_faults;
        unsigned long flags;
        int i;

        if (grp) {
                spin_lock_irqsave(&grp->lock, flags);
                for (i = 0; i < NR_NUMA_HINT_FAULT_STATS * nr_node_ids; i++)
                        grp->faults[i] -= p->numa_faults[i];
                grp->total_faults -= p->total_numa_faults;

                grp->nr_tasks--;
                spin_unlock_irqrestore(&grp->lock, flags);
                RCU_INIT_POINTER(p->numa_group, NULL);
                put_numa_group(grp);
        }

        p->numa_faults = NULL;
        kfree(numa_faults);
}

/*
 * Got a PROT_NONE fault for a page on @node.
 */
void task_numa_fault(int last_cpupid, int mem_node, int pages, int flags)
{
        struct task_struct *p = current;
        bool migrated = flags & TNF_MIGRATED;
        int cpu_node = task_node(current);
        int local = !!(flags & TNF_FAULT_LOCAL);
        struct numa_group *ng;
        int priv;

        if (!static_branch_likely(&sched_numa_balancing))
                return;

        /* for example, ksmd faulting in a user's mm */
        if (!p->mm)
                return;

        /* Allocate buffer to track faults on a per-node basis */
        if (unlikely(!p->numa_faults)) {
                int size = sizeof(*p->numa_faults) *
                           NR_NUMA_HINT_FAULT_BUCKETS * nr_node_ids;

                p->numa_faults = kzalloc(size, GFP_KERNEL|__GFP_NOWARN);
                if (!p->numa_faults)
                        return;

                p->total_numa_faults = 0;
                memset(p->numa_faults_locality, 0, sizeof(p->numa_faults_locality));
        }

        /*
         * First accesses are treated as private, otherwise consider accesses
         * to be private if the accessing pid has not changed
         */
        if (unlikely(last_cpupid == (-1 & LAST_CPUPID_MASK))) {
                priv = 1;
        } else {
                priv = cpupid_match_pid(p, last_cpupid);
                if (!priv && !(flags & TNF_NO_GROUP))
                        task_numa_group(p, last_cpupid, flags, &priv);
        }

        /*
         * If a workload spans multiple NUMA nodes, a shared fault that
         * occurs wholly within the set of nodes that the workload is
         * actively using should be counted as local. This allows the
         * scan rate to slow down when a workload has settled down.
         */
        ng = p->numa_group;
        if (!priv && !local && ng && ng->active_nodes > 1 &&
                                numa_is_active_node(cpu_node, ng) &&
                                numa_is_active_node(mem_node, ng))
                local = 1;

        /*
         * Retry task to preferred node migration periodically, in case it
         * case it previously failed, or the scheduler moved us.
         */
        if (time_after(jiffies, p->numa_migrate_retry)) {
                task_numa_placement(p);
                numa_migrate_preferred(p);
        }

        if (migrated)
                p->numa_pages_migrated += pages;
        if (flags & TNF_MIGRATE_FAIL)
                p->numa_faults_locality[2] += pages;

        p->numa_faults[task_faults_idx(NUMA_MEMBUF, mem_node, priv)] += pages;
        p->numa_faults[task_faults_idx(NUMA_CPUBUF, cpu_node, priv)] += pages;
        p->numa_faults_locality[local] += pages;
}

static void reset_ptenuma_scan(struct task_struct *p)
{
        /*
         * We only did a read acquisition of the mmap sem, so
         * p->mm->numa_scan_seq is written to without exclusive access
         * and the update is not guaranteed to be atomic. That's not
         * much of an issue though, since this is just used for
         * statistical sampling. Use READ_ONCE/WRITE_ONCE, which are not
         * expensive, to avoid any form of compiler optimizations:
         */
        WRITE_ONCE(p->mm->numa_scan_seq, READ_ONCE(p->mm->numa_scan_seq) + 1);
        p->mm->numa_scan_offset = 0;
}

/*
 * The expensive part of numa migration is done from task_work context.
 * Triggered from task_tick_numa().
 */
void task_numa_work(struct callback_head *work)
{
        unsigned long migrate, next_scan, now = jiffies;
        struct task_struct *p = current;
        struct mm_struct *mm = p->mm;
        u64 runtime = p->se.sum_exec_runtime;
        struct vm_area_struct *vma;
        unsigned long start, end;
        unsigned long nr_pte_updates = 0;
        long pages, virtpages;

        SCHED_WARN_ON(p != container_of(work, struct task_struct, numa_work));

        work->next = work; /* protect against double add */
        /*
         * Who cares about NUMA placement when they're dying.
         *
         * NOTE: make sure not to dereference p->mm before this check,
         * exit_task_work() happens _after_ exit_mm() so we could be called
         * without p->mm even though we still had it when we enqueued this
         * work.
         */
        if (p->flags & PF_EXITING)
                return;

        if (!mm->numa_next_scan) {
                mm->numa_next_scan = now +
                        msecs_to_jiffies(sysctl_numa_balancing_scan_delay);
        }

        /*
         * Enforce maximal scan/migration frequency..
         */
        migrate = mm->numa_next_scan;
        if (time_before(now, migrate))
                return;

        if (p->numa_scan_period == 0) {
                p->numa_scan_period_max = task_scan_max(p);
                p->numa_scan_period = task_scan_start(p);
        }

        next_scan = now + msecs_to_jiffies(p->numa_scan_period);
        if (cmpxchg(&mm->numa_next_scan, migrate, next_scan) != migrate)
                return;

        /*
         * Delay this task enough that another task of this mm will likely win
         * the next time around.
         */
        p->node_stamp += 2 * TICK_NSEC;

        start = mm->numa_scan_offset;
        pages = sysctl_numa_balancing_scan_size;
        pages <<= 20 - PAGE_SHIFT; /* MB in pages */
        virtpages = pages * 8;     /* Scan up to this much virtual space */
        if (!pages)
                return;


        if (!down_read_trylock(&mm->mmap_sem))
                return;
        vma = find_vma(mm, start);
        if (!vma) {
                reset_ptenuma_scan(p);
                start = 0;
                vma = mm->mmap;
        }
        for (; vma; vma = vma->vm_next) {
                if (!vma_migratable(vma) || !vma_policy_mof(vma) ||
                        is_vm_hugetlb_page(vma) || (vma->vm_flags & VM_MIXEDMAP)) {
                        continue;
                }

                /*
                 * Shared library pages mapped by multiple processes are not
                 * migrated as it is expected they are cache replicated. Avoid
                 * hinting faults in read-only file-backed mappings or the vdso
                 * as migrating the pages will be of marginal benefit.
                 */
                if (!vma->vm_mm ||
                    (vma->vm_file && (vma->vm_flags & (VM_READ|VM_WRITE)) == (VM_READ)))
                        continue;

                /*
                 * Skip inaccessible VMAs to avoid any confusion between
                 * PROT_NONE and NUMA hinting ptes
                 */
                if (!(vma->vm_flags & (VM_READ | VM_EXEC | VM_WRITE)))
                        continue;

                do {
                        start = max(start, vma->vm_start);
                        end = ALIGN(start + (pages << PAGE_SHIFT), HPAGE_SIZE);
                        end = min(end, vma->vm_end);
                        nr_pte_updates = change_prot_numa(vma, start, end);

                        /*
                         * Try to scan sysctl_numa_balancing_size worth of
                         * hpages that have at least one present PTE that
                         * is not already pte-numa. If the VMA contains
                         * areas that are unused or already full of prot_numa
                         * PTEs, scan up to virtpages, to skip through those
                         * areas faster.
                         */
                        if (nr_pte_updates)
                                pages -= (end - start) >> PAGE_SHIFT;
                        virtpages -= (end - start) >> PAGE_SHIFT;

                        start = end;
                        if (pages <= 0 || virtpages <= 0)
                                goto out;

                        cond_resched();
                } while (end != vma->vm_end);
        }

out:
        /*
         * It is possible to reach the end of the VMA list but the last few
         * VMAs are not guaranteed to the vma_migratable. If they are not, we
         * would find the !migratable VMA on the next scan but not reset the
         * scanner to the start so check it now.
         */
        if (vma)
                mm->numa_scan_offset = start;
        else
                reset_ptenuma_scan(p);
        up_read(&mm->mmap_sem);

        /*
         * Make sure tasks use at least 32x as much time to run other code
         * than they used here, to limit NUMA PTE scanning overhead to 3% max.
         * Usually update_task_scan_period slows down scanning enough; on an
         * overloaded system we need to limit overhead on a per task basis.
         */
        if (unlikely(p->se.sum_exec_runtime != runtime)) {
                u64 diff = p->se.sum_exec_runtime - runtime;
                p->node_stamp += 32 * diff;
        }
}

/*
 * Drive the periodic memory faults..
 */
void task_tick_numa(struct rq *rq, struct task_struct *curr)
{
        struct callback_head *work = &curr->numa_work;
        u64 period, now;

        /*
         * We don't care about NUMA placement if we don't have memory.
         */
        if (!curr->mm || (curr->flags & PF_EXITING) || work->next != work)
                return;

        /*
         * Using runtime rather than walltime has the dual advantage that
         * we (mostly) drive the selection from busy threads and that the
         * task needs to have done some actual work before we bother with
         * NUMA placement.
         */
        now = curr->se.sum_exec_runtime;
        period = (u64)curr->numa_scan_period * NSEC_PER_MSEC;

        if (now > curr->node_stamp + period) {
                if (!curr->node_stamp)
                        curr->numa_scan_period = task_scan_start(curr);
                curr->node_stamp += period;

                if (!time_before(jiffies, curr->mm->numa_next_scan)) {
                        init_task_work(work, task_numa_work); /* TODO: move this into sched_fork() */
                        task_work_add(curr, work, true);
                }
        }
}

#else
static void task_tick_numa(struct rq *rq, struct task_struct *curr)
{
}

static inline void account_numa_enqueue(struct rq *rq, struct task_struct *p)
{
}

static inline void account_numa_dequeue(struct rq *rq, struct task_struct *p)
{
}

#endif /* CONFIG_NUMA_BALANCING */

static void
account_entity_enqueue(struct cfs_rq *cfs_rq, struct sched_entity *se)
{
        update_load_add(&cfs_rq->load, se->load.weight);
        if (!parent_entity(se))
                update_load_add(&rq_of(cfs_rq)->load, se->load.weight);
#ifdef CONFIG_SMP
        if (entity_is_task(se)) {
                struct rq *rq = rq_of(cfs_rq);

                account_numa_enqueue(rq, task_of(se));
                list_add(&se->group_node, &rq->cfs_tasks);
        }
#endif
        cfs_rq->nr_running++;
}

static void
account_entity_dequeue(struct cfs_rq *cfs_rq, struct sched_entity *se)
{
        update_load_sub(&cfs_rq->load, se->load.weight);
        if (!parent_entity(se))
                update_load_sub(&rq_of(cfs_rq)->load, se->load.weight);
#ifdef CONFIG_SMP
        if (entity_is_task(se)) {
                account_numa_dequeue(rq_of(cfs_rq), task_of(se));
                list_del_init(&se->group_node);
        }
#endif
        cfs_rq->nr_running--;
}

/*
 * Signed add and clamp on underflow.
 *
 * Explicitly do a load-store to ensure the intermediate value never hits
 * memory. This allows lockless observations without ever seeing the negative
 * values.
 */
#define add_positive(_ptr, _val) do {                           \
        typeof(_ptr) ptr = (_ptr);                              \
        typeof(_val) val = (_val);                              \
        typeof(*ptr) res, var = READ_ONCE(*ptr);                \
                                                                \
        res = var + val;                                        \
                                                                \
        if (val < 0 && res > var)                               \
                res = 0;                                        \
                                                                \
        WRITE_ONCE(*ptr, res);                                  \
} while (0)

/*
 * Unsigned subtract and clamp on underflow.
 *
 * Explicitly do a load-store to ensure the intermediate value never hits
 * memory. This allows lockless observations without ever seeing the negative
 * values.
 */
#define sub_positive(_ptr, _val) do {                           \
        typeof(_ptr) ptr = (_ptr);                              \
        typeof(*ptr) val = (_val);                              \
        typeof(*ptr) res, var = READ_ONCE(*ptr);                \
        res = var - val;                                        \
        if (res > var)                                          \
                res = 0;                                        \
        WRITE_ONCE(*ptr, res);                                  \
} while (0)

#ifdef CONFIG_SMP
static inline void
enqueue_runnable_load_avg(struct cfs_rq *cfs_rq, struct sched_entity *se)
{
        cfs_rq->runnable_weight += se->runnable_weight;

        cfs_rq->avg.runnable_load_avg += se->avg.runnable_load_avg;
        cfs_rq->avg.runnable_load_sum += se_runnable(se) * se->avg.runnable_load_sum;
}

static inline void
dequeue_runnable_load_avg(struct cfs_rq *cfs_rq, struct sched_entity *se)
{
        cfs_rq->runnable_weight -= se->runnable_weight;

        sub_positive(&cfs_rq->avg.runnable_load_avg, se->avg.runnable_load_avg);
        sub_positive(&cfs_rq->avg.runnable_load_sum,
                     se_runnable(se) * se->avg.runnable_load_sum);
}

static inline void
enqueue_load_avg(struct cfs_rq *cfs_rq, struct sched_entity *se)
{
        cfs_rq->avg.load_avg += se->avg.load_avg;
        cfs_rq->avg.load_sum += se_weight(se) * se->avg.load_sum;
}

static inline void
dequeue_load_avg(struct cfs_rq *cfs_rq, struct sched_entity *se)
{
        sub_positive(&cfs_rq->avg.load_avg, se->avg.load_avg);
        sub_positive(&cfs_rq->avg.load_sum, se_weight(se) * se->avg.load_sum);
}
#else
static inline void
enqueue_runnable_load_avg(struct cfs_rq *cfs_rq, struct sched_entity *se) { }
static inline void
dequeue_runnable_load_avg(struct cfs_rq *cfs_rq, struct sched_entity *se) { }
static inline void
enqueue_load_avg(struct cfs_rq *cfs_rq, struct sched_entity *se) { }
static inline void
dequeue_load_avg(struct cfs_rq *cfs_rq, struct sched_entity *se) { }
#endif

static void reweight_entity(struct cfs_rq *cfs_rq, struct sched_entity *se,
                            unsigned long weight, unsigned long runnable)
{
        if (se->on_rq) {
                /* commit outstanding execution time */
                if (cfs_rq->curr == se)
                        update_curr(cfs_rq);
                account_entity_dequeue(cfs_rq, se);
                dequeue_runnable_load_avg(cfs_rq, se);
        }
        dequeue_load_avg(cfs_rq, se);

        se->runnable_weight = runnable;
        update_load_set(&se->load, weight);

#ifdef CONFIG_SMP
        do {
                u32 divider = LOAD_AVG_MAX - 1024 + se->avg.period_contrib;

                se->avg.load_avg = div_u64(se_weight(se) * se->avg.load_sum, divider);
                se->avg.runnable_load_avg =
                        div_u64(se_runnable(se) * se->avg.runnable_load_sum, divider);
        } while (0);
#endif

        enqueue_load_avg(cfs_rq, se);
        if (se->on_rq) {
                account_entity_enqueue(cfs_rq, se);
                enqueue_runnable_load_avg(cfs_rq, se);
        }
}

void reweight_task(struct task_struct *p, int prio)
{
        struct sched_entity *se = &p->se;
        struct cfs_rq *cfs_rq = cfs_rq_of(se);
        struct load_weight *load = &se->load;
        unsigned long weight = scale_load(sched_prio_to_weight[prio]);

        reweight_entity(cfs_rq, se, weight, weight);
        load->inv_weight = sched_prio_to_wmult[prio];
}

#ifdef CONFIG_FAIR_GROUP_SCHED
#ifdef CONFIG_SMP
/*
 * All this does is approximate the hierarchical proportion which includes that
 * global sum we all love to hate.
 *
 * That is, the weight of a group entity, is the proportional share of the
 * group weight based on the group runqueue weights. That is:
 *
 *                     tg->weight * grq->load.weight
 *   ge->load.weight = -----------------------------               (1)
 *                        \Sum grq->load.weight
 *
 * Now, because computing that sum is prohibitively expensive to compute (been
 * there, done that) we approximate it with this average stuff. The average
 * moves slower and therefore the approximation is cheaper and more stable.
 *
 * So instead of the above, we substitute:
 *
 *   grq->load.weight -> grq->avg.load_avg                         (2)
 *
 * which yields the following:
 *
 *                     tg->weight * grq->avg.load_avg
 *   ge->load.weight = ------------------------------              (3)
 *                              tg->load_avg
 *
 * Where: tg->load_avg ~= \Sum grq->avg.load_avg
 *
 * That is shares_avg, and it is right (given the approximation (2)).
 *
 * The problem with it is that because the average is slow -- it was designed
 * to be exactly that of course -- this leads to transients in boundary
 * conditions. In specific, the case where the group was idle and we start the
 * one task. It takes time for our CPU's grq->avg.load_avg to build up,
 * yielding bad latency etc..
 *
 * Now, in that special case (1) reduces to:
 *
 *                     tg->weight * grq->load.weight
 *   ge->load.weight = ----------------------------- = tg->weight   (4)
 *                          grp->load.weight
 *
 * That is, the sum collapses because all other CPUs are idle; the UP scenario.
 *
 * So what we do is modify our approximation (3) to approach (4) in the (near)
 * UP case, like:
 *
 *   ge->load.weight =
 *
 *              tg->weight * grq->load.weight
 *     ---------------------------------------------------         (5)
 *     tg->load_avg - grq->avg.load_avg + grq->load.weight
 *
 * But because grq->load.weight can drop to 0, resulting in a divide by zero,
 * we need to use grq->avg.load_avg as its lower bound, which then gives:
 *
 *
 *                     tg->weight * grq->load.weight
 *   ge->load.weight = -----------------------------               (6)
 *                              tg_load_avg'
 *
 * Where:
 *
 *   tg_load_avg' = tg->load_avg - grq->avg.load_avg +
 *                  max(grq->load.weight, grq->avg.load_avg)
 *
 * And that is shares_weight and is icky. In the (near) UP case it approaches
 * (4) while in the normal case it approaches (3). It consistently
 * overestimates the ge->load.weight and therefore:
 *
 *   \Sum ge->load.weight >= tg->weight
 *
 * hence icky!
 */
static long calc_group_shares(struct cfs_rq *cfs_rq)
{
        long tg_weight, tg_shares, load, shares;
        struct task_group *tg = cfs_rq->tg;

        tg_shares = READ_ONCE(tg->shares);

        load = max(scale_load_down(cfs_rq->load.weight), cfs_rq->avg.load_avg);

        tg_weight = atomic_long_read(&tg->load_avg);

        /* Ensure tg_weight >= load */
        tg_weight -= cfs_rq->tg_load_avg_contrib;
        tg_weight += load;

        shares = (tg_shares * load);
        if (tg_weight)
                shares /= tg_weight;

        /*
         * MIN_SHARES has to be unscaled here to support per-CPU partitioning
         * of a group with small tg->shares value. It is a floor value which is
         * assigned as a minimum load.weight to the sched_entity representing
         * the group on a CPU.
         *
         * E.g. on 64-bit for a group with tg->shares of scale_load(15)=15*1024
         * on an 8-core system with 8 tasks each runnable on one CPU shares has
         * to be 15*1024*1/8=1920 instead of scale_load(MIN_SHARES)=2*1024. In
         * case no task is runnable on a CPU MIN_SHARES=2 should be returned
         * instead of 0.
         */
        return clamp_t(long, shares, MIN_SHARES, tg_shares);
}

/*
 * This calculates the effective runnable weight for a group entity based on
 * the group entity weight calculated above.
 *
 * Because of the above approximation (2), our group entity weight is
 * an load_avg based ratio (3). This means that it includes blocked load and
 * does not represent the runnable weight.
 *
 * Approximate the group entity's runnable weight per ratio from the group
 * runqueue:
 *
 *                                           grq->avg.runnable_load_avg
 *   ge->runnable_weight = ge->load.weight * -------------------------- (7)
 *                                               grq->avg.load_avg
 *
 * However, analogous to above, since the avg numbers are slow, this leads to
 * transients in the from-idle case. Instead we use:
 *
 *   ge->runnable_weight = ge->load.weight *
 *
 *              max(grq->avg.runnable_load_avg, grq->runnable_weight)
 *              -----------------------------------------------------   (8)
 *                    max(grq->avg.load_avg, grq->load.weight)
 *
 * Where these max() serve both to use the 'instant' values to fix the slow
 * from-idle and avoid the /0 on to-idle, similar to (6).
 */
static long calc_group_runnable(struct cfs_rq *cfs_rq, long shares)
{
        long runnable, load_avg;

        load_avg = max(cfs_rq->avg.load_avg,
                       scale_load_down(cfs_rq->load.weight));

        runnable = max(cfs_rq->avg.runnable_load_avg,
                       scale_load_down(cfs_rq->runnable_weight));

        runnable *= shares;
        if (load_avg)
                runnable /= load_avg;

        return clamp_t(long, runnable, MIN_SHARES, shares);
}
#endif /* CONFIG_SMP */

static inline int throttled_hierarchy(struct cfs_rq *cfs_rq);

/*
 * Recomputes the group entity based on the current state of its group
 * runqueue.
 */
static void update_cfs_group(struct sched_entity *se)
{
        struct cfs_rq *gcfs_rq = group_cfs_rq(se);
        long shares, runnable;

        if (!gcfs_rq)
                return;

        if (throttled_hierarchy(gcfs_rq))
                return;

#ifndef CONFIG_SMP
        runnable = shares = READ_ONCE(gcfs_rq->tg->shares);

        if (likely(se->load.weight == shares))
                return;
#else
        shares   = calc_group_shares(gcfs_rq);
        runnable = calc_group_runnable(gcfs_rq, shares);
#endif

        reweight_entity(cfs_rq_of(se), se, shares, runnable);
}

#else /* CONFIG_FAIR_GROUP_SCHED */
static inline void update_cfs_group(struct sched_entity *se)
{
}
#endif /* CONFIG_FAIR_GROUP_SCHED */

static inline void cfs_rq_util_change(struct cfs_rq *cfs_rq, int flags)
{
        struct rq *rq = rq_of(cfs_rq);

        if (&rq->cfs == cfs_rq || (flags & SCHED_CPUFREQ_MIGRATION)) {
                /*
                 * There are a few boundary cases this might miss but it should
                 * get called often enough that that should (hopefully) not be
                 * a real problem.
                 *
                 * It will not get called when we go idle, because the idle
                 * thread is a different class (!fair), nor will the utilization
                 * number include things like RT tasks.
                 *
                 * As is, the util number is not freq-invariant (we'd have to
                 * implement arch_scale_freq_capacity() for that).
                 *
                 * See cpu_util().
                 */
                cpufreq_update_util(rq, flags);
        }
}

#ifdef CONFIG_SMP
#ifdef CONFIG_FAIR_GROUP_SCHED
/**
 * update_tg_load_avg - update the tg's load avg
 * @cfs_rq: the cfs_rq whose avg changed
 * @force: update regardless of how small the difference
 *
 * This function 'ensures': tg->load_avg := \Sum tg->cfs_rq[]->avg.load.
 * However, because tg->load_avg is a global value there are performance
 * considerations.
 *
 * In order to avoid having to look at the other cfs_rq's, we use a
 * differential update where we store the last value we propagated. This in
 * turn allows skipping updates if the differential is 'small'.
 *
 * Updating tg's load_avg is necessary before update_cfs_share().
 */
static inline void update_tg_load_avg(struct cfs_rq *cfs_rq, int force)
{
        long delta = cfs_rq->avg.load_avg - cfs_rq->tg_load_avg_contrib;

        /*
         * No need to update load_avg for root_task_group as it is not used.
         */
        if (cfs_rq->tg == &root_task_group)
                return;

        if (force || abs(delta) > cfs_rq->tg_load_avg_contrib / 64) {
                atomic_long_add(delta, &cfs_rq->tg->load_avg);
                cfs_rq->tg_load_avg_contrib = cfs_rq->avg.load_avg;
        }
}

/*
 * Called within set_task_rq() right before setting a task's CPU. The
 * caller only guarantees p->pi_lock is held; no other assumptions,
 * including the state of rq->lock, should be made.
 */
void set_task_rq_fair(struct sched_entity *se,
                      struct cfs_rq *prev, struct cfs_rq *next)
{
        u64 p_last_update_time;
        u64 n_last_update_time;

        if (!sched_feat(ATTACH_AGE_LOAD))
                return;

        /*
         * We are supposed to update the task to "current" time, then its up to
         * date and ready to go to new CPU/cfs_rq. But we have difficulty in
         * getting what current time is, so simply throw away the out-of-date
         * time. This will result in the wakee task is less decayed, but giving
         * the wakee more load sounds not bad.
         */
        if (!(se->avg.last_update_time && prev))
                return;

#ifndef CONFIG_64BIT
        {
                u64 p_last_update_time_copy;
                u64 n_last_update_time_copy;

                do {
                        p_last_update_time_copy = prev->load_last_update_time_copy;
                        n_last_update_time_copy = next->load_last_update_time_copy;

                        smp_rmb();

                        p_last_update_time = prev->avg.last_update_time;
                        n_last_update_time = next->avg.last_update_time;

                } while (p_last_update_time != p_last_update_time_copy ||
                         n_last_update_time != n_last_update_time_copy);
        }
#else
        p_last_update_time = prev->avg.last_update_time;
        n_last_update_time = next->avg.last_update_time;
#endif
        __update_load_avg_blocked_se(p_last_update_time, cpu_of(rq_of(prev)), se);
        se->avg.last_update_time = n_last_update_time;
}


/*
 * When on migration a sched_entity joins/leaves the PELT hierarchy, we need to
 * propagate its contribution. The key to this propagation is the invariant
 * that for each group:
 *
 *   ge->avg == grq->avg                                                (1)
 *
 * _IFF_ we look at the pure running and runnable sums. Because they
 * represent the very same entity, just at different points in the hierarchy.
 *
 * Per the above update_tg_cfs_util() is trivial and simply copies the running
 * sum over (but still wrong, because the group entity and group rq do not have
 * their PELT windows aligned).
 *
 * However, update_tg_cfs_runnable() is more complex. So we have:
 *
 *   ge->avg.load_avg = ge->load.weight * ge->avg.runnable_avg          (2)
 *
 * And since, like util, the runnable part should be directly transferable,
 * the following would _appear_ to be the straight forward approach:
 *
 *   grq->avg.load_avg = grq->load.weight * grq->avg.runnable_avg       (3)
 *
 * And per (1) we have:
 *
 *   ge->avg.runnable_avg == grq->avg.runnable_avg
 *
 * Which gives:
 *
 *                      ge->load.weight * grq->avg.load_avg
 *   ge->avg.load_avg = -----------------------------------             (4)
 *                               grq->load.weight
 *
 * Except that is wrong!
 *
 * Because while for entities historical weight is not important and we
 * really only care about our future and therefore can consider a pure
 * runnable sum, runqueues can NOT do this.
 *
 * We specifically want runqueues to have a load_avg that includes
 * historical weights. Those represent the blocked load, the load we expect
 * to (shortly) return to us. This only works by keeping the weights as
 * integral part of the sum. We therefore cannot decompose as per (3).
 *
 * Another reason this doesn't work is that runnable isn't a 0-sum entity.
 * Imagine a rq with 2 tasks that each are runnable 2/3 of the time. Then the
 * rq itself is runnable anywhere between 2/3 and 1 depending on how the
 * runnable section of these tasks overlap (or not). If they were to perfectly
 * align the rq as a whole would be runnable 2/3 of the time. If however we
 * always have at least 1 runnable task, the rq as a whole is always runnable.
 *
 * So we'll have to approximate.. :/
 *
 * Given the constraint:
 *
 *   ge->avg.running_sum <= ge->avg.runnable_sum <= LOAD_AVG_MAX
 *
 * We can construct a rule that adds runnable to a rq by assuming minimal
 * overlap.
 *
 * On removal, we'll assume each task is equally runnable; which yields:
 *
 *   grq->avg.runnable_sum = grq->avg.load_sum / grq->load.weight
 *
 * XXX: only do this for the part of runnable > running ?
 *
 */

static inline void
update_tg_cfs_util(struct cfs_rq *cfs_rq, struct sched_entity *se, struct cfs_rq *gcfs_rq)
{
        long delta = gcfs_rq->avg.util_avg - se->avg.util_avg;

        /* Nothing to update */
        if (!delta)
                return;

        /*
         * The relation between sum and avg is:
         *
         *   LOAD_AVG_MAX - 1024 + sa->period_contrib
         *
         * however, the PELT windows are not aligned between grq and gse.
         */

        /* Set new sched_entity's utilization */
        se->avg.util_avg = gcfs_rq->avg.util_avg;
        se->avg.util_sum = se->avg.util_avg * LOAD_AVG_MAX;

        /* Update parent cfs_rq utilization */
        add_positive(&cfs_rq->avg.util_avg, delta);
        cfs_rq->avg.util_sum = cfs_rq->avg.util_avg * LOAD_AVG_MAX;
}

static inline void
update_tg_cfs_runnable(struct cfs_rq *cfs_rq, struct sched_entity *se, struct cfs_rq *gcfs_rq)
{
        long delta_avg, running_sum, runnable_sum = gcfs_rq->prop_runnable_sum;
        unsigned long runnable_load_avg, load_avg;
        u64 runnable_load_sum, load_sum = 0;
        s64 delta_sum;

        if (!runnable_sum)
                return;

        gcfs_rq->prop_runnable_sum = 0;

        if (runnable_sum >= 0) {
                /*
                 * Add runnable; clip at LOAD_AVG_MAX. Reflects that until
                 * the CPU is saturated running == runnable.
                 */
                runnable_sum += se->avg.load_sum;
                runnable_sum = min(runnable_sum, (long)LOAD_AVG_MAX);
        } else {
                /*
                 * Estimate the new unweighted runnable_sum of the gcfs_rq by
                 * assuming all tasks are equally runnable.
                 */
                if (scale_load_down(gcfs_rq->load.weight)) {
                        load_sum = div_s64(gcfs_rq->avg.load_sum,
                                scale_load_down(gcfs_rq->load.weight));
                }

                /* But make sure to not inflate se's runnable */
                runnable_sum = min(se->avg.load_sum, load_sum);
        }

        /*
         * runnable_sum can't be lower than running_sum
         * As running sum is scale with CPU capacity wehreas the runnable sum
         * is not we rescale running_sum 1st
         */
        running_sum = se->avg.util_sum /
                arch_scale_cpu_capacity(NULL, cpu_of(rq_of(cfs_rq)));
        runnable_sum = max(runnable_sum, running_sum);

        load_sum = (s64)se_weight(se) * runnable_sum;
        load_avg = div_s64(load_sum, LOAD_AVG_MAX);

        delta_sum = load_sum - (s64)se_weight(se) * se->avg.load_sum;
        delta_avg = load_avg - se->avg.load_avg;

        se->avg.load_sum = runnable_sum;
        se->avg.load_avg = load_avg;
        add_positive(&cfs_rq->avg.load_avg, delta_avg);
        add_positive(&cfs_rq->avg.load_sum, delta_sum);

        runnable_load_sum = (s64)se_runnable(se) * runnable_sum;
        runnable_load_avg = div_s64(runnable_load_sum, LOAD_AVG_MAX);
        delta_sum = runnable_load_sum - se_weight(se) * se->avg.runnable_load_sum;
        delta_avg = runnable_load_avg - se->avg.runnable_load_avg;

        se->avg.runnable_load_sum = runnable_sum;
        se->avg.runnable_load_avg = runnable_load_avg;

        if (se->on_rq) {
                add_positive(&cfs_rq->avg.runnable_load_avg, delta_avg);
                add_positive(&cfs_rq->avg.runnable_load_sum, delta_sum);
        }
}

static inline void add_tg_cfs_propagate(struct cfs_rq *cfs_rq, long runnable_sum)
{
        cfs_rq->propagate = 1;
        cfs_rq->prop_runnable_sum += runnable_sum;
}

/* Update task and its cfs_rq load average */
static inline int propagate_entity_load_avg(struct sched_entity *se)
{
        struct cfs_rq *cfs_rq, *gcfs_rq;

        if (entity_is_task(se))
                return 0;

        gcfs_rq = group_cfs_rq(se);
        if (!gcfs_rq->propagate)
                return 0;

        gcfs_rq->propagate = 0;

        cfs_rq = cfs_rq_of(se);

        add_tg_cfs_propagate(cfs_rq, gcfs_rq->prop_runnable_sum);

        update_tg_cfs_util(cfs_rq, se, gcfs_rq);
        update_tg_cfs_runnable(cfs_rq, se, gcfs_rq);

        return 1;
}

/*
 * Check if we need to update the load and the utilization of a blocked
 * group_entity:
 */
static inline bool skip_blocked_update(struct sched_entity *se)
{
        struct cfs_rq *gcfs_rq = group_cfs_rq(se);

        /*
         * If sched_entity still have not zero load or utilization, we have to
         * decay it:
         */
        if (se->avg.load_avg || se->avg.util_avg)
                return false;

        /*
         * If there is a pending propagation, we have to update the load and
         * the utilization of the sched_entity:
         */
        if (gcfs_rq->propagate)
                return false;

        /*
         * Otherwise, the load and the utilization of the sched_entity is
         * already zero and there is no pending propagation, so it will be a
         * waste of time to try to decay it:
         */
        return true;
}

#else /* CONFIG_FAIR_GROUP_SCHED */

static inline void update_tg_load_avg(struct cfs_rq *cfs_rq, int force) {}

static inline int propagate_entity_load_avg(struct sched_entity *se)
{
        return 0;
}

static inline void add_tg_cfs_propagate(struct cfs_rq *cfs_rq, long runnable_sum) {}

#endif /* CONFIG_FAIR_GROUP_SCHED */

/**
 * update_cfs_rq_load_avg - update the cfs_rq's load/util averages
 * @now: current time, as per cfs_rq_clock_task()
 * @cfs_rq: cfs_rq to update
 *
 * The cfs_rq avg is the direct sum of all its entities (blocked and runnable)
 * avg. The immediate corollary is that all (fair) tasks must be attached, see
 * post_init_entity_util_avg().
 *
 * cfs_rq->avg is used for task_h_load() and update_cfs_share() for example.
 *
 * Returns true if the load decayed or we removed load.
 *
 * Since both these conditions indicate a changed cfs_rq->avg.load we should
 * call update_tg_load_avg() when this function returns true.
 */
static inline int
update_cfs_rq_load_avg(u64 now, struct cfs_rq *cfs_rq)
{
        unsigned long removed_load = 0, removed_util = 0, removed_runnable_sum = 0;
        struct sched_avg *sa = &cfs_rq->avg;
        int decayed = 0;

        if (cfs_rq->removed.nr) {
                unsigned long r;
                u32 divider = LOAD_AVG_MAX - 1024 + sa->period_contrib;

                raw_spin_lock(&cfs_rq->removed.lock);
                swap(cfs_rq->removed.util_avg, removed_util);
                swap(cfs_rq->removed.load_avg, removed_load);
                swap(cfs_rq->removed.runnable_sum, removed_runnable_sum);
                cfs_rq->removed.nr = 0;
                raw_spin_unlock(&cfs_rq->removed.lock);

                r = removed_load;
                sub_positive(&sa->load_avg, r);
                sub_positive(&sa->load_sum, r * divider);

                r = removed_util;
                sub_positive(&sa->util_avg, r);
                sub_positive(&sa->util_sum, r * divider);

                add_tg_cfs_propagate(cfs_rq, -(long)removed_runnable_sum);

                decayed = 1;
        }

        decayed |= __update_load_avg_cfs_rq(now, cpu_of(rq_of(cfs_rq)), cfs_rq);

#ifndef CONFIG_64BIT
        smp_wmb();
        cfs_rq->load_last_update_time_copy = sa->last_update_time;
#endif

        if (decayed)
                cfs_rq_util_change(cfs_rq, 0);

        return decayed;
}

/**
 * attach_entity_load_avg - attach this entity to its cfs_rq load avg
 * @cfs_rq: cfs_rq to attach to
 * @se: sched_entity to attach
 * @flags: migration hints
 *
 * Must call update_cfs_rq_load_avg() before this, since we rely on
 * cfs_rq->avg.last_update_time being current.
 */
static void attach_entity_load_avg(struct cfs_rq *cfs_rq, struct sched_entity *se, int flags)
{
        u32 divider = LOAD_AVG_MAX - 1024 + cfs_rq->avg.period_contrib;

        /*
         * When we attach the @se to the @cfs_rq, we must align the decay
         * window because without that, really weird and wonderful things can
         * happen.
         *
         * XXX illustrate
         */
        se->avg.last_update_time = cfs_rq->avg.last_update_time;
        se->avg.period_contrib = cfs_rq->avg.period_contrib;

        /*
         * Hell(o) Nasty stuff.. we need to recompute _sum based on the new
         * period_contrib. This isn't strictly correct, but since we're
         * entirely outside of the PELT hierarchy, nobody cares if we truncate
         * _sum a little.
         */
        se->avg.util_sum = se->avg.util_avg * divider;

        se->avg.load_sum = divider;
        if (se_weight(se)) {
                se->avg.load_sum =
                        div_u64(se->avg.load_avg * se->avg.load_sum, se_weight(se));
        }

        se->avg.runnable_load_sum = se->avg.load_sum;

        enqueue_load_avg(cfs_rq, se);
        cfs_rq->avg.util_avg += se->avg.util_avg;
        cfs_rq->avg.util_sum += se->avg.util_sum;

        add_tg_cfs_propagate(cfs_rq, se->avg.load_sum);

        cfs_rq_util_change(cfs_rq, flags);
}

/**
 * detach_entity_load_avg - detach this entity from its cfs_rq load avg
 * @cfs_rq: cfs_rq to detach from
 * @se: sched_entity to detach
 *
 * Must call update_cfs_rq_load_avg() before this, since we rely on
 * cfs_rq->avg.last_update_time being current.
 */
static void detach_entity_load_avg(struct cfs_rq *cfs_rq, struct sched_entity *se)
{
        dequeue_load_avg(cfs_rq, se);
        sub_positive(&cfs_rq->avg.util_avg, se->avg.util_avg);
        sub_positive(&cfs_rq->avg.util_sum, se->avg.util_sum);

        add_tg_cfs_propagate(cfs_rq, -se->avg.load_sum);

        cfs_rq_util_change(cfs_rq, 0);
}

/*
 * Optional action to be done while updating the load average
 */
#define UPDATE_TG       0x1
#define SKIP_AGE_LOAD   0x2
#define DO_ATTACH       0x4

/* Update task and its cfs_rq load average */
static inline void update_load_avg(struct cfs_rq *cfs_rq, struct sched_entity *se, int flags)
{
        u64 now = cfs_rq_clock_task(cfs_rq);
        struct rq *rq = rq_of(cfs_rq);
        int cpu = cpu_of(rq);
        int decayed;

        /*
         * Track task load average for carrying it to new CPU after migrated, and
         * track group sched_entity load average for task_h_load calc in migration
         */
        if (se->avg.last_update_time && !(flags & SKIP_AGE_LOAD))
                __update_load_avg_se(now, cpu, cfs_rq, se);

        decayed  = update_cfs_rq_load_avg(now, cfs_rq);
        decayed |= propagate_entity_load_avg(se);

        if (!se->avg.last_update_time && (flags & DO_ATTACH)) {

                /*
                 * DO_ATTACH means we're here from enqueue_entity().
                 * !last_update_time means we've passed through
                 * migrate_task_rq_fair() indicating we migrated.
                 *
                 * IOW we're enqueueing a task on a new CPU.
                 */
                attach_entity_load_avg(cfs_rq, se, SCHED_CPUFREQ_MIGRATION);
                update_tg_load_avg(cfs_rq, 0);

        } else if (decayed && (flags & UPDATE_TG))
                update_tg_load_avg(cfs_rq, 0);
}

#ifndef CONFIG_64BIT
static inline u64 cfs_rq_last_update_time(struct cfs_rq *cfs_rq)
{
        u64 last_update_time_copy;
        u64 last_update_time;

        do {
                last_update_time_copy = cfs_rq->load_last_update_time_copy;
                smp_rmb();
                last_update_time = cfs_rq->avg.last_update_time;
        } while (last_update_time != last_update_time_copy);

        return last_update_time;
}
#else
static inline u64 cfs_rq_last_update_time(struct cfs_rq *cfs_rq)
{
        return cfs_rq->avg.last_update_time;
}
#endif

/*
 * Synchronize entity load avg of dequeued entity without locking
 * the previous rq.
 */
void sync_entity_load_avg(struct sched_entity *se)
{
        struct cfs_rq *cfs_rq = cfs_rq_of(se);
        u64 last_update_time;

        last_update_time = cfs_rq_last_update_time(cfs_rq);
        __update_load_avg_blocked_se(last_update_time, cpu_of(rq_of(cfs_rq)), se);
}

/*
 * Task first catches up with cfs_rq, and then subtract
 * itself from the cfs_rq (task must be off the queue now).
 */
void remove_entity_load_avg(struct sched_entity *se)
{
        struct cfs_rq *cfs_rq = cfs_rq_of(se);
        unsigned long flags;

        /*
         * tasks cannot exit without having gone through wake_up_new_task() ->
         * post_init_entity_util_avg() which will have added things to the
         * cfs_rq, so we can remove unconditionally.
         *
         * Similarly for groups, they will have passed through
         * post_init_entity_util_avg() before unregister_sched_fair_group()
         * calls this.
         */

        sync_entity_load_avg(se);

        raw_spin_lock_irqsave(&cfs_rq->removed.lock, flags);
        ++cfs_rq->removed.nr;
        cfs_rq->removed.util_avg        += se->avg.util_avg;
        cfs_rq->removed.load_avg        += se->avg.load_avg;
        cfs_rq->removed.runnable_sum    += se->avg.load_sum; /* == runnable_sum */
        raw_spin_unlock_irqrestore(&cfs_rq->removed.lock, flags);
}

static inline unsigned long cfs_rq_runnable_load_avg(struct cfs_rq *cfs_rq)
{
        return cfs_rq->avg.runnable_load_avg;
}

static inline unsigned long cfs_rq_load_avg(struct cfs_rq *cfs_rq)
{
        return cfs_rq->avg.load_avg;
}

static int idle_balance(struct rq *this_rq, struct rq_flags *rf);

static inline unsigned long task_util(struct task_struct *p)
{
        return READ_ONCE(p->se.avg.util_avg);
}

static inline unsigned long _task_util_est(struct task_struct *p)
{
        struct util_est ue = READ_ONCE(p->se.avg.util_est);

        return max(ue.ewma, ue.enqueued);
}

static inline unsigned long task_util_est(struct task_struct *p)
{
        return max(task_util(p), _task_util_est(p));
}

static inline void util_est_enqueue(struct cfs_rq *cfs_rq,
                                    struct task_struct *p)
{
        unsigned int enqueued;

        if (!sched_feat(UTIL_EST))
                return;

        /* Update root cfs_rq's estimated utilization */
        enqueued  = cfs_rq->avg.util_est.enqueued;
        enqueued += (_task_util_est(p) | UTIL_AVG_UNCHANGED);
        WRITE_ONCE(cfs_rq->avg.util_est.enqueued, enqueued);
}

/*
 * Check if a (signed) value is within a specified (unsigned) margin,
 * based on the observation that:
 *
 *     abs(x) < y := (unsigned)(x + y - 1) < (2 * y - 1)
 *
 * NOTE: this only works when value + maring < INT_MAX.
 */
static inline bool within_margin(int value, int margin)
{
        return ((unsigned int)(value + margin - 1) < (2 * margin - 1));
}

static void
util_est_dequeue(struct cfs_rq *cfs_rq, struct task_struct *p, bool task_sleep)
{
        long last_ewma_diff;
        struct util_est ue;

        if (!sched_feat(UTIL_EST))
                return;

        /* Update root cfs_rq's estimated utilization */
        ue.enqueued  = cfs_rq->avg.util_est.enqueued;
        ue.enqueued -= min_t(unsigned int, ue.enqueued,
                             (_task_util_est(p) | UTIL_AVG_UNCHANGED));
        WRITE_ONCE(cfs_rq->avg.util_est.enqueued, ue.enqueued);

        /*
         * Skip update of task's estimated utilization when the task has not
         * yet completed an activation, e.g. being migrated.
         */
        if (!task_sleep)
                return;

        /*
         * If the PELT values haven't changed since enqueue time,
         * skip the util_est update.
         */
        ue = p->se.avg.util_est;
        if (ue.enqueued & UTIL_AVG_UNCHANGED)
                return;

        /*
         * Skip update of task's estimated utilization when its EWMA is
         * already ~1% close to its last activation value.
         */
        ue.enqueued = (task_util(p) | UTIL_AVG_UNCHANGED);
        last_ewma_diff = ue.enqueued - ue.ewma;
        if (within_margin(last_ewma_diff, (SCHED_CAPACITY_SCALE / 100)))
                return;

        /*
         * Update Task's estimated utilization
         *
         * When *p completes an activation we can consolidate another sample
         * of the task size. This is done by storing the current PELT value
         * as ue.enqueued and by using this value to update the Exponential
         * Weighted Moving Average (EWMA):
         *
         *  ewma(t) = w *  task_util(p) + (1-w) * ewma(t-1)
         *          = w *  task_util(p) +         ewma(t-1)  - w * ewma(t-1)
         *          = w * (task_util(p) -         ewma(t-1)) +     ewma(t-1)
         *          = w * (      last_ewma_diff            ) +     ewma(t-1)
         *          = w * (last_ewma_diff  +  ewma(t-1) / w)
         *
         * Where 'w' is the weight of new samples, which is configured to be
         * 0.25, thus making w=1/4 ( >>= UTIL_EST_WEIGHT_SHIFT)
         */
        ue.ewma <<= UTIL_EST_WEIGHT_SHIFT;
        ue.ewma  += last_ewma_diff;
        ue.ewma >>= UTIL_EST_WEIGHT_SHIFT;
        WRITE_ONCE(p->se.avg.util_est, ue);
}

#else /* CONFIG_SMP */

#define UPDATE_TG       0x0
#define SKIP_AGE_LOAD   0x0
#define DO_ATTACH       0x0

static inline void update_load_avg(struct cfs_rq *cfs_rq, struct sched_entity *se, int not_used1)
{
        cfs_rq_util_change(cfs_rq, 0);
}

static inline void remove_entity_load_avg(struct sched_entity *se) {}

static inline void
attach_entity_load_avg(struct cfs_rq *cfs_rq, struct sched_entity *se, int flags) {}
static inline void
detach_entity_load_avg(struct cfs_rq *cfs_rq, struct sched_entity *se) {}

static inline int idle_balance(struct rq *rq, struct rq_flags *rf)
{
        return 0;
}

static inline void
util_est_enqueue(struct cfs_rq *cfs_rq, struct task_struct *p) {}

static inline void
util_est_dequeue(struct cfs_rq *cfs_rq, struct task_struct *p,
                 bool task_sleep) {}

#endif /* CONFIG_SMP */

static void check_spread(struct cfs_rq *cfs_rq, struct sched_entity *se)
{
#ifdef CONFIG_SCHED_DEBUG
        s64 d = se->vruntime - cfs_rq->min_vruntime;

        if (d < 0)
                d = -d;

        if (d > 3*sysctl_sched_latency)
                schedstat_inc(cfs_rq->nr_spread_over);
#endif
}

static void
place_entity(struct cfs_rq *cfs_rq, struct sched_entity *se, int initial)
{
        u64 vruntime = cfs_rq->min_vruntime;

        /*
         * The 'current' period is already promised to the current tasks,
         * however the extra weight of the new task will slow them down a
         * little, place the new task so that it fits in the slot that
         * stays open at the end.
         */
        if (initial && sched_feat(START_DEBIT))
                vruntime += sched_vslice(cfs_rq, se);

        /* sleeps up to a single latency don't count. */
        if (!initial) {
                unsigned long thresh = sysctl_sched_latency;

                /*
                 * Halve their sleep time's effect, to allow
                 * for a gentler effect of sleepers:
                 */
                if (sched_feat(GENTLE_FAIR_SLEEPERS))
                        thresh >>= 1;

                vruntime -= thresh;
        }

        /* ensure we never gain time by being placed backwards. */
        se->vruntime = max_vruntime(se->vruntime, vruntime);
}

static void check_enqueue_throttle(struct cfs_rq *cfs_rq);

static inline void check_schedstat_required(void)
{
#ifdef CONFIG_SCHEDSTATS
        if (schedstat_enabled())
                return;

        /* Force schedstat enabled if a dependent tracepoint is active */
        if (trace_sched_stat_wait_enabled()    ||
                        trace_sched_stat_sleep_enabled()   ||
                        trace_sched_stat_iowait_enabled()  ||
                        trace_sched_stat_blocked_enabled() ||
                        trace_sched_stat_runtime_enabled())  {
                printk_deferred_once("Scheduler tracepoints stat_sleep, stat_iowait, "
                             "stat_blocked and stat_runtime require the "
                             "kernel parameter schedstats=enable or "
                             "kernel.sched_schedstats=1\n");
        }
#endif
}


/*
 * MIGRATION
 *
 *      dequeue
 *        update_curr()
 *          update_min_vruntime()
 *        vruntime -= min_vruntime
 *
 *      enqueue
 *        update_curr()
 *          update_min_vruntime()
 *        vruntime += min_vruntime
 *
 * this way the vruntime transition between RQs is done when both
 * min_vruntime are up-to-date.
 *
 * WAKEUP (remote)
 *
 *      ->migrate_task_rq_fair() (p->state == TASK_WAKING)
 *        vruntime -= min_vruntime
 *
 *      enqueue
 *        update_curr()
 *          update_min_vruntime()
 *        vruntime += min_vruntime
 *
 * this way we don't have the most up-to-date min_vruntime on the originating
 * CPU and an up-to-date min_vruntime on the destination CPU.
 */

static void
enqueue_entity(struct cfs_rq *cfs_rq, struct sched_entity *se, int flags)
{
        bool renorm = !(flags & ENQUEUE_WAKEUP) || (flags & ENQUEUE_MIGRATED);
        bool curr = cfs_rq->curr == se;

        /*
         * If we're the current task, we must renormalise before calling
         * update_curr().
         */
        if (renorm && curr)
                se->vruntime += cfs_rq->min_vruntime;

        update_curr(cfs_rq);

        /*
         * Otherwise, renormalise after, such that we're placed at the current
         * moment in time, instead of some random moment in the past. Being
         * placed in the past could significantly boost this task to the
         * fairness detriment of existing tasks.
         */
        if (renorm && !curr)
                se->vruntime += cfs_rq->min_vruntime;

        /*
         * When enqueuing a sched_entity, we must:
         *   - Update loads to have both entity and cfs_rq synced with now.
         *   - Add its load to cfs_rq->runnable_avg
         *   - For group_entity, update its weight to reflect the new share of
         *     its group cfs_rq
         *   - Add its new weight to cfs_rq->load.weight
         */
        update_load_avg(cfs_rq, se, UPDATE_TG | DO_ATTACH);
        update_cfs_group(se);
        enqueue_runnable_load_avg(cfs_rq, se);
        account_entity_enqueue(cfs_rq, se);

        if (flags & ENQUEUE_WAKEUP)
                place_entity(cfs_rq, se, 0);

        check_schedstat_required();
        update_stats_enqueue(cfs_rq, se, flags);
        check_spread(cfs_rq, se);
        if (!curr)
                __enqueue_entity(cfs_rq, se);
        se->on_rq = 1;

        if (cfs_rq->nr_running == 1) {
                list_add_leaf_cfs_rq(cfs_rq);
                check_enqueue_throttle(cfs_rq);
        }
}

static void __clear_buddies_last(struct sched_entity *se)
{
        for_each_sched_entity(se) {
                struct cfs_rq *cfs_rq = cfs_rq_of(se);
                if (cfs_rq->last != se)
                        break;

                cfs_rq->last = NULL;
        }
}

static void __clear_buddies_next(struct sched_entity *se)
{
        for_each_sched_entity(se) {
                struct cfs_rq *cfs_rq = cfs_rq_of(se);
                if (cfs_rq->next != se)
                        break;

                cfs_rq->next = NULL;
        }
}

static void __clear_buddies_skip(struct sched_entity *se)
{
        for_each_sched_entity(se) {
                struct cfs_rq *cfs_rq = cfs_rq_of(se);
                if (cfs_rq->skip != se)
                        break;

                cfs_rq->skip = NULL;
        }
}

static void clear_buddies(struct cfs_rq *cfs_rq, struct sched_entity *se)
{
        if (cfs_rq->last == se)
                __clear_buddies_last(se);

        if (cfs_rq->next == se)
                __clear_buddies_next(se);

        if (cfs_rq->skip == se)
                __clear_buddies_skip(se);
}

static __always_inline void return_cfs_rq_runtime(struct cfs_rq *cfs_rq);

static void
dequeue_entity(struct cfs_rq *cfs_rq, struct sched_entity *se, int flags)
{
        /*
         * Update run-time statistics of the 'current'.
         */
        update_curr(cfs_rq);

        /*
         * When dequeuing a sched_entity, we must:
         *   - Update loads to have both entity and cfs_rq synced with now.
         *   - Substract its load from the cfs_rq->runnable_avg.
         *   - Substract its previous weight from cfs_rq->load.weight.
         *   - For group entity, update its weight to reflect the new share
         *     of its group cfs_rq.
         */
        update_load_avg(cfs_rq, se, UPDATE_TG);
        dequeue_runnable_load_avg(cfs_rq, se);

        update_stats_dequeue(cfs_rq, se, flags);

        clear_buddies(cfs_rq, se);

        if (se != cfs_rq->curr)
                __dequeue_entity(cfs_rq, se);
        se->on_rq = 0;
        account_entity_dequeue(cfs_rq, se);

        /*
         * Normalize after update_curr(); which will also have moved
         * min_vruntime if @se is the one holding it back. But before doing
         * update_min_vruntime() again, which will discount @se's position and
         * can move min_vruntime forward still more.
         */
        if (!(flags & DEQUEUE_SLEEP))
                se->vruntime -= cfs_rq->min_vruntime;

        /* return excess runtime on last dequeue */
        return_cfs_rq_runtime(cfs_rq);

        update_cfs_group(se);

        /*
         * Now advance min_vruntime if @se was the entity holding it back,
         * except when: DEQUEUE_SAVE && !DEQUEUE_MOVE, in this case we'll be
         * put back on, and if we advance min_vruntime, we'll be placed back
         * further than we started -- ie. we'll be penalized.
         */
        if ((flags & (DEQUEUE_SAVE | DEQUEUE_MOVE)) == DEQUEUE_SAVE)
                update_min_vruntime(cfs_rq);
}

/*
 * Preempt the current task with a newly woken task if needed:
 */
static void
check_preempt_tick(struct cfs_rq *cfs_rq, struct sched_entity *curr)
{
        unsigned long ideal_runtime, delta_exec;
        struct sched_entity *se;
        s64 delta;

        ideal_runtime = sched_slice(cfs_rq, curr);
        delta_exec = curr->sum_exec_runtime - curr->prev_sum_exec_runtime;
        if (delta_exec > ideal_runtime) {
                resched_curr(rq_of(cfs_rq));
                /*
                 * The current task ran long enough, ensure it doesn't get
                 * re-elected due to buddy favours.
                 */
                clear_buddies(cfs_rq, curr);
                return;
        }

        /*
         * Ensure that a task that missed wakeup preemption by a
         * narrow margin doesn't have to wait for a full slice.
         * This also mitigates buddy induced latencies under load.
         */
        if (delta_exec < sysctl_sched_min_granularity)
                return;

        se = __pick_first_entity(cfs_rq);
        delta = curr->vruntime - se->vruntime;

        if (delta < 0)
                return;

        if (delta > ideal_runtime)
                resched_curr(rq_of(cfs_rq));
}

static void
set_next_entity(struct cfs_rq *cfs_rq, struct sched_entity *se)
{
        /* 'current' is not kept within the tree. */
        if (se->on_rq) {
                /*
                 * Any task has to be enqueued before it get to execute on
                 * a CPU. So account for the time it spent waiting on the
                 * runqueue.
                 */
                update_stats_wait_end(cfs_rq, se);
                __dequeue_entity(cfs_rq, se);
                update_load_avg(cfs_rq, se, UPDATE_TG);
        }

        update_stats_curr_start(cfs_rq, se);
        cfs_rq->curr = se;

        /*
         * Track our maximum slice length, if the CPU's load is at
         * least twice that of our own weight (i.e. dont track it
         * when there are only lesser-weight tasks around):
         */
        if (schedstat_enabled() && rq_of(cfs_rq)->load.weight >= 2*se->load.weight) {
                schedstat_set(se->statistics.slice_max,
                        max((u64)schedstat_val(se->statistics.slice_max),
                            se->sum_exec_runtime - se->prev_sum_exec_runtime));
        }

        se->prev_sum_exec_runtime = se->sum_exec_runtime;
}

static int
wakeup_preempt_entity(struct sched_entity *curr, struct sched_entity *se);

/*
 * Pick the next process, keeping these things in mind, in this order:
 * 1) keep things fair between processes/task groups
 * 2) pick the "next" process, since someone really wants that to run
 * 3) pick the "last" process, for cache locality
 * 4) do not run the "skip" process, if something else is available
 */
static struct sched_entity *
pick_next_entity(struct cfs_rq *cfs_rq, struct sched_entity *curr)
{
        struct sched_entity *left = __pick_first_entity(cfs_rq);
        struct sched_entity *se;

        /*
         * If curr is set we have to see if its left of the leftmost entity
         * still in the tree, provided there was anything in the tree at all.
         */
        if (!left || (curr && entity_before(curr, left)))
                left = curr;

        se = left; /* ideally we run the leftmost entity */

        /*
         * Avoid running the skip buddy, if running something else can
         * be done without getting too unfair.
         */
        if (cfs_rq->skip == se) {
                struct sched_entity *second;

                if (se == curr) {
                        second = __pick_first_entity(cfs_rq);
                } else {
                        second = __pick_next_entity(se);
                        if (!second || (curr && entity_before(curr, second)))
                                second = curr;
                }

                if (second && wakeup_preempt_entity(second, left) < 1)
                        se = second;
        }

        /*
         * Prefer last buddy, try to return the CPU to a preempted task.
         */
        if (cfs_rq->last && wakeup_preempt_entity(cfs_rq->last, left) < 1)
                se = cfs_rq->last;

        /*
         * Someone really wants this to run. If it's not unfair, run it.
         */
        if (cfs_rq->next && wakeup_preempt_entity(cfs_rq->next, left) < 1)
                se = cfs_rq->next;

        clear_buddies(cfs_rq, se);

        return se;
}

static bool check_cfs_rq_runtime(struct cfs_rq *cfs_rq);

static void put_prev_entity(struct cfs_rq *cfs_rq, struct sched_entity *prev)
{
        /*
         * If still on the runqueue then deactivate_task()
         * was not called and update_curr() has to be done:
         */
        if (prev->on_rq)
                update_curr(cfs_rq);

        /* throttle cfs_rqs exceeding runtime */
        check_cfs_rq_runtime(cfs_rq);

        check_spread(cfs_rq, prev);

        if (prev->on_rq) {
                update_stats_wait_start(cfs_rq, prev);
                /* Put 'current' back into the tree. */
                __enqueue_entity(cfs_rq, prev);
                /* in !on_rq case, update occurred at dequeue */
                update_load_avg(cfs_rq, prev, 0);
        }
        cfs_rq->curr = NULL;
}

static void
entity_tick(struct cfs_rq *cfs_rq, struct sched_entity *curr, int queued)
{
        /*
         * Update run-time statistics of the 'current'.
         */
        update_curr(cfs_rq);

        /*
         * Ensure that runnable average is periodically updated.
         */
        update_load_avg(cfs_rq, curr, UPDATE_TG);
        update_cfs_group(curr);

#ifdef CONFIG_SCHED_HRTICK
        /*
         * queued ticks are scheduled to match the slice, so don't bother
         * validating it and just reschedule.
         */
        if (queued) {
                resched_curr(rq_of(cfs_rq));
                return;
        }
        /*
         * don't let the period tick interfere with the hrtick preemption
         */
        if (!sched_feat(DOUBLE_TICK) &&
                        hrtimer_active(&rq_of(cfs_rq)->hrtick_timer))
                return;
#endif

        if (cfs_rq->nr_running > 1)
                check_preempt_tick(cfs_rq, curr);
}


/**************************************************
 * CFS bandwidth control machinery
 */

#ifdef CONFIG_CFS_BANDWIDTH

#ifdef HAVE_JUMP_LABEL
static struct static_key __cfs_bandwidth_used;

static inline bool cfs_bandwidth_used(void)
{
        return static_key_false(&__cfs_bandwidth_used);
}

void cfs_bandwidth_usage_inc(void)
{
        static_key_slow_inc_cpuslocked(&__cfs_bandwidth_used);
}

void cfs_bandwidth_usage_dec(void)
{
        static_key_slow_dec_cpuslocked(&__cfs_bandwidth_used);
}
#else /* HAVE_JUMP_LABEL */
static bool cfs_bandwidth_used(void)
{
        return true;
}

void cfs_bandwidth_usage_inc(void) {}
void cfs_bandwidth_usage_dec(void) {}
#endif /* HAVE_JUMP_LABEL */

/*
 * default period for cfs group bandwidth.
 * default: 0.1s, units: nanoseconds
 */
static inline u64 default_cfs_period(void)
{
        return 100000000ULL;
}

static inline u64 sched_cfs_bandwidth_slice(void)
{
        return (u64)sysctl_sched_cfs_bandwidth_slice * NSEC_PER_USEC;
}

/*
 * Replenish runtime according to assigned quota and update expiration time.
 * We use sched_clock_cpu directly instead of rq->clock to avoid adding
 * additional synchronization around rq->lock.
 *
 * requires cfs_b->lock
 */
void __refill_cfs_bandwidth_runtime(struct cfs_bandwidth *cfs_b)
{
        u64 now;

        if (cfs_b->quota == RUNTIME_INF)
                return;

        now = sched_clock_cpu(smp_processor_id());
        cfs_b->runtime = cfs_b->quota;
        cfs_b->runtime_expires = now + ktime_to_ns(cfs_b->period);
        cfs_b->expires_seq++;
}

static inline struct cfs_bandwidth *tg_cfs_bandwidth(struct task_group *tg)
{
        return &tg->cfs_bandwidth;
}

/* rq->task_clock normalized against any time this cfs_rq has spent throttled */
static inline u64 cfs_rq_clock_task(struct cfs_rq *cfs_rq)
{
        if (unlikely(cfs_rq->throttle_count))
                return cfs_rq->throttled_clock_task - cfs_rq->throttled_clock_task_time;

        return rq_clock_task(rq_of(cfs_rq)) - cfs_rq->throttled_clock_task_time;
}

/* returns 0 on failure to allocate runtime */
static int assign_cfs_rq_runtime(struct cfs_rq *cfs_rq)
{
        struct task_group *tg = cfs_rq->tg;
        struct cfs_bandwidth *cfs_b = tg_cfs_bandwidth(tg);
        u64 amount = 0, min_amount, expires;
        int expires_seq;

        /* note: this is a positive sum as runtime_remaining <= 0 */
        min_amount = sched_cfs_bandwidth_slice() - cfs_rq->runtime_remaining;

        raw_spin_lock(&cfs_b->lock);
        if (cfs_b->quota == RUNTIME_INF)
                amount = min_amount;
        else {
                start_cfs_bandwidth(cfs_b);

                if (cfs_b->runtime > 0) {
                        amount = min(cfs_b->runtime, min_amount);
                        cfs_b->runtime -= amount;
                        cfs_b->idle = 0;
                }
        }
        expires_seq = cfs_b->expires_seq;
        expires = cfs_b->runtime_expires;
        raw_spin_unlock(&cfs_b->lock);

        cfs_rq->runtime_remaining += amount;
        /*
         * we may have advanced our local expiration to account for allowed
         * spread between our sched_clock and the one on which runtime was
         * issued.
         */
        if (cfs_rq->expires_seq != expires_seq) {
                cfs_rq->expires_seq = expires_seq;
                cfs_rq->runtime_expires = expires;
        }

        return cfs_rq->runtime_remaining > 0;
}

/*
 * Note: This depends on the synchronization provided by sched_clock and the
 * fact that rq->clock snapshots this value.
 */
static void expire_cfs_rq_runtime(struct cfs_rq *cfs_rq)
{
        struct cfs_bandwidth *cfs_b = tg_cfs_bandwidth(cfs_rq->tg);

        /* if the deadline is ahead of our clock, nothing to do */
        if (likely((s64)(rq_clock(rq_of(cfs_rq)) - cfs_rq->runtime_expires) < 0))
                return;

        if (cfs_rq->runtime_remaining < 0)
                return;

        /*
         * If the local deadline has passed we have to consider the
         * possibility that our sched_clock is 'fast' and the global deadline
         * has not truly expired.
         *
         * Fortunately we can check determine whether this the case by checking
         * whether the global deadline(cfs_b->expires_seq) has advanced.
         */
        if (cfs_rq->expires_seq == cfs_b->expires_seq) {
                /* extend local deadline, drift is bounded above by 2 ticks */
                cfs_rq->runtime_expires += TICK_NSEC;
        } else {
                /* global deadline is ahead, expiration has passed */
                cfs_rq->runtime_remaining = 0;
        }
}

static void __account_cfs_rq_runtime(struct cfs_rq *cfs_rq, u64 delta_exec)
{
        /* dock delta_exec before expiring quota (as it could span periods) */
        cfs_rq->runtime_remaining -= delta_exec;
        expire_cfs_rq_runtime(cfs_rq);

        if (likely(cfs_rq->runtime_remaining > 0))
                return;

        /*
         * if we're unable to extend our runtime we resched so that the active
         * hierarchy can be throttled
         */
        if (!assign_cfs_rq_runtime(cfs_rq) && likely(cfs_rq->curr))
                resched_curr(rq_of(cfs_rq));
}

static __always_inline
void account_cfs_rq_runtime(struct cfs_rq *cfs_rq, u64 delta_exec)
{
        if (!cfs_bandwidth_used() || !cfs_rq->runtime_enabled)
                return;

        __account_cfs_rq_runtime(cfs_rq, delta_exec);
}

static inline int cfs_rq_throttled(struct cfs_rq *cfs_rq)
{
        return cfs_bandwidth_used() && cfs_rq->throttled;
}

/* check whether cfs_rq, or any parent, is throttled */
static inline int throttled_hierarchy(struct cfs_rq *cfs_rq)
{
        return cfs_bandwidth_used() && cfs_rq->throttle_count;
}

/*
 * Ensure that neither of the group entities corresponding to src_cpu or
 * dest_cpu are members of a throttled hierarchy when performing group
 * load-balance operations.
 */
static inline int throttled_lb_pair(struct task_group *tg,
                                    int src_cpu, int dest_cpu)
{
        struct cfs_rq *src_cfs_rq, *dest_cfs_rq;

        src_cfs_rq = tg->cfs_rq[src_cpu];
        dest_cfs_rq = tg->cfs_rq[dest_cpu];

        return throttled_hierarchy(src_cfs_rq) ||
               throttled_hierarchy(dest_cfs_rq);
}

static int tg_unthrottle_up(struct task_group *tg, void *data)
{
        struct rq *rq = data;
        struct cfs_rq *cfs_rq = tg->cfs_rq[cpu_of(rq)];

        cfs_rq->throttle_count--;
        if (!cfs_rq->throttle_count) {
                /* adjust cfs_rq_clock_task() */
                cfs_rq->throttled_clock_task_time += rq_clock_task(rq) -
                                             cfs_rq->throttled_clock_task;
        }

        return 0;
}

static int tg_throttle_down(struct task_group *tg, void *data)
{
        struct rq *rq = data;
        struct cfs_rq *cfs_rq = tg->cfs_rq[cpu_of(rq)];

        /* group is entering throttled state, stop time */
        if (!cfs_rq->throttle_count)
                cfs_rq->throttled_clock_task = rq_clock_task(rq);
        cfs_rq->throttle_count++;

        return 0;
}

static void throttle_cfs_rq(struct cfs_rq *cfs_rq)
{
        struct rq *rq = rq_of(cfs_rq);
        struct cfs_bandwidth *cfs_b = tg_cfs_bandwidth(cfs_rq->tg);
        struct sched_entity *se;
        long task_delta, dequeue = 1;
        bool empty;

        se = cfs_rq->tg->se[cpu_of(rq_of(cfs_rq))];

        /* freeze hierarchy runnable averages while throttled */
        rcu_read_lock();
        walk_tg_tree_from(cfs_rq->tg, tg_throttle_down, tg_nop, (void *)rq);
        rcu_read_unlock();

        task_delta = cfs_rq->h_nr_running;
        for_each_sched_entity(se) {
                struct cfs_rq *qcfs_rq = cfs_rq_of(se);
                /* throttled entity or throttle-on-deactivate */
                if (!se->on_rq)
                        break;

                if (dequeue)
                        dequeue_entity(qcfs_rq, se, DEQUEUE_SLEEP);
                qcfs_rq->h_nr_running -= task_delta;

                if (qcfs_rq->load.weight)
                        dequeue = 0;
        }

        if (!se)
                sub_nr_running(rq, task_delta);

        cfs_rq->throttled = 1;
        cfs_rq->throttled_clock = rq_clock(rq);
        raw_spin_lock(&cfs_b->lock);
        empty = list_empty(&cfs_b->throttled_cfs_rq);

        /*
         * Add to the _head_ of the list, so that an already-started
         * distribute_cfs_runtime will not see us
         */
        list_add_rcu(&cfs_rq->throttled_list, &cfs_b->throttled_cfs_rq);

        /*
         * If we're the first throttled task, make sure the bandwidth
         * timer is running.
         */
        if (empty)
                start_cfs_bandwidth(cfs_b);

        raw_spin_unlock(&cfs_b->lock);
}

void unthrottle_cfs_rq(struct cfs_rq *cfs_rq)
{
        struct rq *rq = rq_of(cfs_rq);
        struct cfs_bandwidth *cfs_b = tg_cfs_bandwidth(cfs_rq->tg);
        struct sched_entity *se;
        int enqueue = 1;
        long task_delta;

        se = cfs_rq->tg->se[cpu_of(rq)];

        cfs_rq->throttled = 0;

        update_rq_clock(rq);

        raw_spin_lock(&cfs_b->lock);
        cfs_b->throttled_time += rq_clock(rq) - cfs_rq->throttled_clock;
        list_del_rcu(&cfs_rq->throttled_list);
        raw_spin_unlock(&cfs_b->lock);

        /* update hierarchical throttle state */
        walk_tg_tree_from(cfs_rq->tg, tg_nop, tg_unthrottle_up, (void *)rq);

        if (!cfs_rq->load.weight)
                return;

        task_delta = cfs_rq->h_nr_running;
        for_each_sched_entity(se) {
                if (se->on_rq)
                        enqueue = 0;

                cfs_rq = cfs_rq_of(se);
                if (enqueue)
                        enqueue_entity(cfs_rq, se, ENQUEUE_WAKEUP);
                cfs_rq->h_nr_running += task_delta;

                if (cfs_rq_throttled(cfs_rq))
                        break;
        }

        if (!se)
                add_nr_running(rq, task_delta);

        /* Determine whether we need to wake up potentially idle CPU: */
        if (rq->curr == rq->idle && rq->cfs.nr_running)
                resched_curr(rq);
}

static u64 distribute_cfs_runtime(struct cfs_bandwidth *cfs_b,
                u64 remaining, u64 expires)
{
        struct cfs_rq *cfs_rq;
        u64 runtime;
        u64 starting_runtime = remaining;

        rcu_read_lock();
        list_for_each_entry_rcu(cfs_rq, &cfs_b->throttled_cfs_rq,
                                throttled_list) {
                struct rq *rq = rq_of(cfs_rq);
                struct rq_flags rf;

                rq_lock(rq, &rf);
                if (!cfs_rq_throttled(cfs_rq))
                        goto next;

                runtime = -cfs_rq->runtime_remaining + 1;
                if (runtime > remaining)
                        runtime = remaining;
                remaining -= runtime;

                cfs_rq->runtime_remaining += runtime;
                cfs_rq->runtime_expires = expires;

                /* we check whether we're throttled above */
                if (cfs_rq->runtime_remaining > 0)
                        unthrottle_cfs_rq(cfs_rq);

next:
                rq_unlock(rq, &rf);

                if (!remaining)
                        break;
        }
        rcu_read_unlock();

        return starting_runtime - remaining;
}

/*
 * Responsible for refilling a task_group's bandwidth and unthrottling its
 * cfs_rqs as appropriate. If there has been no activity within the last
 * period the timer is deactivated until scheduling resumes; cfs_b->idle is
 * used to track this state.
 */
static int do_sched_cfs_period_timer(struct cfs_bandwidth *cfs_b, int overrun)
{
        u64 runtime, runtime_expires;
        int throttled;

        /* no need to continue the timer with no bandwidth constraint */
        if (cfs_b->quota == RUNTIME_INF)
                goto out_deactivate;

        throttled = !list_empty(&cfs_b->throttled_cfs_rq);
        cfs_b->nr_periods += overrun;

        /*
         * idle depends on !throttled (for the case of a large deficit), and if
         * we're going inactive then everything else can be deferred
         */
        if (cfs_b->idle && !throttled)
                goto out_deactivate;

        __refill_cfs_bandwidth_runtime(cfs_b);

        if (!throttled) {
                /* mark as potentially idle for the upcoming period */
                cfs_b->idle = 1;
                return 0;
        }

        /* account preceding periods in which throttling occurred */
        cfs_b->nr_throttled += overrun;

        runtime_expires = cfs_b->runtime_expires;

        /*
         * This check is repeated as we are holding onto the new bandwidth while
         * we unthrottle. This can potentially race with an unthrottled group
         * trying to acquire new bandwidth from the global pool. This can result
         * in us over-using our runtime if it is all used during this loop, but
         * only by limited amounts in that extreme case.
         */
        while (throttled && cfs_b->runtime > 0) {
                runtime = cfs_b->runtime;
                raw_spin_unlock(&cfs_b->lock);
                /* we can't nest cfs_b->lock while distributing bandwidth */
                runtime = distribute_cfs_runtime(cfs_b, runtime,
                                                 runtime_expires);
                raw_spin_lock(&cfs_b->lock);

                throttled = !list_empty(&cfs_b->throttled_cfs_rq);

                cfs_b->runtime -= min(runtime, cfs_b->runtime);
        }

        /*
         * While we are ensured activity in the period following an
         * unthrottle, this also covers the case in which the new bandwidth is
         * insufficient to cover the existing bandwidth deficit.  (Forcing the
         * timer to remain active while there are any throttled entities.)
         */
        cfs_b->idle = 0;

        return 0;

out_deactivate:
        return 1;
}

/* a cfs_rq won't donate quota below this amount */
static const u64 min_cfs_rq_runtime = 1 * NSEC_PER_MSEC;
/* minimum remaining period time to redistribute slack quota */
static const u64 min_bandwidth_expiration = 2 * NSEC_PER_MSEC;
/* how long we wait to gather additional slack before distributing */
static const u64 cfs_bandwidth_slack_period = 5 * NSEC_PER_MSEC;

/*
 * Are we near the end of the current quota period?
 *
 * Requires cfs_b->lock for hrtimer_expires_remaining to be safe against the
 * hrtimer base being cleared by hrtimer_start. In the case of
 * migrate_hrtimers, base is never cleared, so we are fine.
 */
static int runtime_refresh_within(struct cfs_bandwidth *cfs_b, u64 min_expire)
{
        struct hrtimer *refresh_timer = &cfs_b->period_timer;
        u64 remaining;

        /* if the call-back is running a quota refresh is already occurring */
        if (hrtimer_callback_running(refresh_timer))
                return 1;

        /* is a quota refresh about to occur? */
        remaining = ktime_to_ns(hrtimer_expires_remaining(refresh_timer));
        if (remaining < min_expire)
                return 1;

        return 0;
}

static void start_cfs_slack_bandwidth(struct cfs_bandwidth *cfs_b)
{
        u64 min_left = cfs_bandwidth_slack_period + min_bandwidth_expiration;

        /* if there's a quota refresh soon don't bother with slack */
        if (runtime_refresh_within(cfs_b, min_left))
                return;

        hrtimer_start(&cfs_b->slack_timer,
                        ns_to_ktime(cfs_bandwidth_slack_period),
                        HRTIMER_MODE_REL);
}

/* we know any runtime found here is valid as update_curr() precedes return */
static void __return_cfs_rq_runtime(struct cfs_rq *cfs_rq)
{
        struct cfs_bandwidth *cfs_b = tg_cfs_bandwidth(cfs_rq->tg);
        s64 slack_runtime = cfs_rq->runtime_remaining - min_cfs_rq_runtime;

        if (slack_runtime <= 0)
                return;

        raw_spin_lock(&cfs_b->lock);
        if (cfs_b->quota != RUNTIME_INF &&
            cfs_rq->runtime_expires == cfs_b->runtime_expires) {
                cfs_b->runtime += slack_runtime;

                /* we are under rq->lock, defer unthrottling using a timer */
                if (cfs_b->runtime > sched_cfs_bandwidth_slice() &&
                    !list_empty(&cfs_b->throttled_cfs_rq))
                        start_cfs_slack_bandwidth(cfs_b);
        }
        raw_spin_unlock(&cfs_b->lock);

        /* even if it's not valid for return we don't want to try again */
        cfs_rq->runtime_remaining -= slack_runtime;
}

static __always_inline void return_cfs_rq_runtime(struct cfs_rq *cfs_rq)
{
        if (!cfs_bandwidth_used())
                return;

        if (!cfs_rq->runtime_enabled || cfs_rq->nr_running)
                return;

        __return_cfs_rq_runtime(cfs_rq);
}

/*
 * This is done with a timer (instead of inline with bandwidth return) since
 * it's necessary to juggle rq->locks to unthrottle their respective cfs_rqs.
 */
static void do_sched_cfs_slack_timer(struct cfs_bandwidth *cfs_b)
{
        u64 runtime = 0, slice = sched_cfs_bandwidth_slice();
        u64 expires;

        /* confirm we're still not at a refresh boundary */
        raw_spin_lock(&cfs_b->lock);
        if (runtime_refresh_within(cfs_b, min_bandwidth_expiration)) {
                raw_spin_unlock(&cfs_b->lock);
                return;
        }

        if (cfs_b->quota != RUNTIME_INF && cfs_b->runtime > slice)
                runtime = cfs_b->runtime;

        expires = cfs_b->runtime_expires;
        raw_spin_unlock(&cfs_b->lock);

        if (!runtime)
                return;

        runtime = distribute_cfs_runtime(cfs_b, runtime, expires);

        raw_spin_lock(&cfs_b->lock);
        if (expires == cfs_b->runtime_expires)
                cfs_b->runtime -= min(runtime, cfs_b->runtime);
        raw_spin_unlock(&cfs_b->lock);
}

/*
 * When a group wakes up we want to make sure that its quota is not already
 * expired/exceeded, otherwise it may be allowed to steal additional ticks of
 * runtime as update_curr() throttling can not not trigger until it's on-rq.
 */
static void check_enqueue_throttle(struct cfs_rq *cfs_rq)
{
        if (!cfs_bandwidth_used())
                return;

        /* an active group must be handled by the update_curr()->put() path */
        if (!cfs_rq->runtime_enabled || cfs_rq->curr)
                return;

        /* ensure the group is not already throttled */
        if (cfs_rq_throttled(cfs_rq))
                return;

        /* update runtime allocation */
        account_cfs_rq_runtime(cfs_rq, 0);
        if (cfs_rq->runtime_remaining <= 0)
                throttle_cfs_rq(cfs_rq);
}

static void sync_throttle(struct task_group *tg, int cpu)
{
        struct cfs_rq *pcfs_rq, *cfs_rq;

        if (!cfs_bandwidth_used())
                return;

        if (!tg->parent)
                return;

        cfs_rq = tg->cfs_rq[cpu];
        pcfs_rq = tg->parent->cfs_rq[cpu];

        cfs_rq->throttle_count = pcfs_rq->throttle_count;
        cfs_rq->throttled_clock_task = rq_clock_task(cpu_rq(cpu));
}

/* conditionally throttle active cfs_rq's from put_prev_entity() */
static bool check_cfs_rq_runtime(struct cfs_rq *cfs_rq)
{
        if (!cfs_bandwidth_used())
                return false;

        if (likely(!cfs_rq->runtime_enabled || cfs_rq->runtime_remaining > 0))
                return false;

        /*
         * it's possible for a throttled entity to be forced into a running
         * state (e.g. set_curr_task), in this case we're finished.
         */
        if (cfs_rq_throttled(cfs_rq))
                return true;

        throttle_cfs_rq(cfs_rq);
        return true;
}

static enum hrtimer_restart sched_cfs_slack_timer(struct hrtimer *timer)
{
        struct cfs_bandwidth *cfs_b =
                container_of(timer, struct cfs_bandwidth, slack_timer);

        do_sched_cfs_slack_timer(cfs_b);

        return HRTIMER_NORESTART;
}

static enum hrtimer_restart sched_cfs_period_timer(struct hrtimer *timer)
{
        struct cfs_bandwidth *cfs_b =
                container_of(timer, struct cfs_bandwidth, period_timer);
        int overrun;
        int idle = 0;

        raw_spin_lock(&cfs_b->lock);
        for (;;) {
                overrun = hrtimer_forward_now(timer, cfs_b->period);
                if (!overrun)
                        break;

                idle = do_sched_cfs_period_timer(cfs_b, overrun);
        }
        if (idle)
                cfs_b->period_active = 0;
        raw_spin_unlock(&cfs_b->lock);

        return idle ? HRTIMER_NORESTART : HRTIMER_RESTART;
}

void init_cfs_bandwidth(struct cfs_bandwidth *cfs_b)
{
        raw_spin_lock_init(&cfs_b->lock);
        cfs_b->runtime = 0;
        cfs_b->quota = RUNTIME_INF;
        cfs_b->period = ns_to_ktime(default_cfs_period());

        INIT_LIST_HEAD(&cfs_b->throttled_cfs_rq);
        hrtimer_init(&cfs_b->period_timer, CLOCK_MONOTONIC, HRTIMER_MODE_ABS_PINNED);
        cfs_b->period_timer.function = sched_cfs_period_timer;
        hrtimer_init(&cfs_b->slack_timer, CLOCK_MONOTONIC, HRTIMER_MODE_REL);
        cfs_b->slack_timer.function = sched_cfs_slack_timer;
}

static void init_cfs_rq_runtime(struct cfs_rq *cfs_rq)
{
        cfs_rq->runtime_enabled = 0;
        INIT_LIST_HEAD(&cfs_rq->throttled_list);
}

void start_cfs_bandwidth(struct cfs_bandwidth *cfs_b)
{
        u64 overrun;

        lockdep_assert_held(&cfs_b->lock);

        if (cfs_b->period_active)
                return;

        cfs_b->period_active = 1;
        overrun = hrtimer_forward_now(&cfs_b->period_timer, cfs_b->period);
        cfs_b->runtime_expires += (overrun + 1) * ktime_to_ns(cfs_b->period);
        cfs_b->expires_seq++;
        hrtimer_start_expires(&cfs_b->period_timer, HRTIMER_MODE_ABS_PINNED);
}

static void destroy_cfs_bandwidth(struct cfs_bandwidth *cfs_b)
{
        /* init_cfs_bandwidth() was not called */
        if (!cfs_b->throttled_cfs_rq.next)
                return;

        hrtimer_cancel(&cfs_b->period_timer);
        hrtimer_cancel(&cfs_b->slack_timer);
}

/*
 * Both these CPU hotplug callbacks race against unregister_fair_sched_group()
 *
 * The race is harmless, since modifying bandwidth settings of unhooked group
 * bits doesn't do much.
 */

/* cpu online calback */
static void __maybe_unused update_runtime_enabled(struct rq *rq)
{
        struct task_group *tg;

        lockdep_assert_held(&rq->lock);

        rcu_read_lock();
        list_for_each_entry_rcu(tg, &task_groups, list) {
                struct cfs_bandwidth *cfs_b = &tg->cfs_bandwidth;
                struct cfs_rq *cfs_rq = tg->cfs_rq[cpu_of(rq)];

                raw_spin_lock(&cfs_b->lock);
                cfs_rq->runtime_enabled = cfs_b->quota != RUNTIME_INF;
                raw_spin_unlock(&cfs_b->lock);
        }
        rcu_read_unlock();
}

/* cpu offline callback */
static void __maybe_unused unthrottle_offline_cfs_rqs(struct rq *rq)
{
        struct task_group *tg;

        lockdep_assert_held(&rq->lock);

        rcu_read_lock();
        list_for_each_entry_rcu(tg, &task_groups, list) {
                struct cfs_rq *cfs_rq = tg->cfs_rq[cpu_of(rq)];

                if (!cfs_rq->runtime_enabled)
                        continue;

                /*
                 * clock_task is not advancing so we just need to make sure
                 * there's some valid quota amount
                 */
                cfs_rq->runtime_remaining = 1;
                /*
                 * Offline rq is schedulable till CPU is completely disabled
                 * in take_cpu_down(), so we prevent new cfs throttling here.
                 */
                cfs_rq->runtime_enabled = 0;

                if (cfs_rq_throttled(cfs_rq))
                        unthrottle_cfs_rq(cfs_rq);
        }
        rcu_read_unlock();
}

#else /* CONFIG_CFS_BANDWIDTH */
static inline u64 cfs_rq_clock_task(struct cfs_rq *cfs_rq)
{
        return rq_clock_task(rq_of(cfs_rq));
}

static void account_cfs_rq_runtime(struct cfs_rq *cfs_rq, u64 delta_exec) {}
static bool check_cfs_rq_runtime(struct cfs_rq *cfs_rq) { return false; }
static void check_enqueue_throttle(struct cfs_rq *cfs_rq) {}
static inline void sync_throttle(struct task_group *tg, int cpu) {}
static __always_inline void return_cfs_rq_runtime(struct cfs_rq *cfs_rq) {}

static inline int cfs_rq_throttled(struct cfs_rq *cfs_rq)
{
        return 0;
}

static inline int throttled_hierarchy(struct cfs_rq *cfs_rq)
{
        return 0;
}

static inline int throttled_lb_pair(struct task_group *tg,
                                    int src_cpu, int dest_cpu)
{
        return 0;
}

void init_cfs_bandwidth(struct cfs_bandwidth *cfs_b) {}

#ifdef CONFIG_FAIR_GROUP_SCHED
static void init_cfs_rq_runtime(struct cfs_rq *cfs_rq) {}
#endif

static inline struct cfs_bandwidth *tg_cfs_bandwidth(struct task_group *tg)
{
        return NULL;
}
static inline void destroy_cfs_bandwidth(struct cfs_bandwidth *cfs_b) {}
static inline void update_runtime_enabled(struct rq *rq) {}
static inline void unthrottle_offline_cfs_rqs(struct rq *rq) {}

#endif /* CONFIG_CFS_BANDWIDTH */

/**************************************************
 * CFS operations on tasks:
 */

#ifdef CONFIG_SCHED_HRTICK
static void hrtick_start_fair(struct rq *rq, struct task_struct *p)
{
        struct sched_entity *se = &p->se;
        struct cfs_rq *cfs_rq = cfs_rq_of(se);

        SCHED_WARN_ON(task_rq(p) != rq);

        if (rq->cfs.h_nr_running > 1) {
                u64 slice = sched_slice(cfs_rq, se);
                u64 ran = se->sum_exec_runtime - se->prev_sum_exec_runtime;
                s64 delta = slice - ran;

                if (delta < 0) {
                        if (rq->curr == p)
                                resched_curr(rq);
                        return;
                }
                hrtick_start(rq, delta);
        }
}

/*
 * called from enqueue/dequeue and updates the hrtick when the
 * current task is from our class and nr_running is low enough
 * to matter.
 */
static void hrtick_update(struct rq *rq)
{
        struct task_struct *curr = rq->curr;

        if (!hrtick_enabled(rq) || curr->sched_class != &fair_sched_class)
                return;

        if (cfs_rq_of(&curr->se)->nr_running < sched_nr_latency)
                hrtick_start_fair(rq, curr);
}
#else /* !CONFIG_SCHED_HRTICK */
static inline void
hrtick_start_fair(struct rq *rq, struct task_struct *p)
{
}

static inline void hrtick_update(struct rq *rq)
{
}
#endif

/*
 * The enqueue_task method is called before nr_running is
 * increased. Here we update the fair scheduling stats and
 * then put the task into the rbtree:
 */
static void
enqueue_task_fair(struct rq *rq, struct task_struct *p, int flags)
{
        struct cfs_rq *cfs_rq;
        struct sched_entity *se = &p->se;

        /*
         * The code below (indirectly) updates schedutil which looks at
         * the cfs_rq utilization to select a frequency.
         * Let's add the task's estimated utilization to the cfs_rq's
         * estimated utilization, before we update schedutil.
         */
        util_est_enqueue(&rq->cfs, p);

        /*
         * If in_iowait is set, the code below may not trigger any cpufreq
         * utilization updates, so do it here explicitly with the IOWAIT flag
         * passed.
         */
        if (p->in_iowait)
                cpufreq_update_util(rq, SCHED_CPUFREQ_IOWAIT);

        for_each_sched_entity(se) {
                if (se->on_rq)
                        break;
                cfs_rq = cfs_rq_of(se);
                enqueue_entity(cfs_rq, se, flags);

                /*
                 * end evaluation on encountering a throttled cfs_rq
                 *
                 * note: in the case of encountering a throttled cfs_rq we will
                 * post the final h_nr_running increment below.
                 */
                if (cfs_rq_throttled(cfs_rq))
                        break;
                cfs_rq->h_nr_running++;

                flags = ENQUEUE_WAKEUP;
        }

        for_each_sched_entity(se) {
                cfs_rq = cfs_rq_of(se);
                cfs_rq->h_nr_running++;

                if (cfs_rq_throttled(cfs_rq))
                        break;

                update_load_avg(cfs_rq, se, UPDATE_TG);
                update_cfs_group(se);
        }

        if (!se)
                add_nr_running(rq, 1);

        hrtick_update(rq);
}

static void set_next_buddy(struct sched_entity *se);

/*
 * The dequeue_task method is called before nr_running is
 * decreased. We remove the task from the rbtree and
 * update the fair scheduling stats:
 */
static void dequeue_task_fair(struct rq *rq, struct task_struct *p, int flags)
{
        struct cfs_rq *cfs_rq;
        struct sched_entity *se = &p->se;
        int task_sleep = flags & DEQUEUE_SLEEP;

        for_each_sched_entity(se) {
                cfs_rq = cfs_rq_of(se);
                dequeue_entity(cfs_rq, se, flags);

                /*
                 * end evaluation on encountering a throttled cfs_rq
                 *
                 * note: in the case of encountering a throttled cfs_rq we will
                 * post the final h_nr_running decrement below.
                */
                if (cfs_rq_throttled(cfs_rq))
                        break;
                cfs_rq->h_nr_running--;

                /* Don't dequeue parent if it has other entities besides us */
                if (cfs_rq->load.weight) {
                        /* Avoid re-evaluating load for this entity: */
                        se = parent_entity(se);
                        /*
                         * Bias pick_next to pick a task from this cfs_rq, as
                         * p is sleeping when it is within its sched_slice.
                         */
                        if (task_sleep && se && !throttled_hierarchy(cfs_rq))
                                set_next_buddy(se);
                        break;
                }
                flags |= DEQUEUE_SLEEP;
        }

        for_each_sched_entity(se) {
                cfs_rq = cfs_rq_of(se);
                cfs_rq->h_nr_running--;

                if (cfs_rq_throttled(cfs_rq))
                        break;

                update_load_avg(cfs_rq, se, UPDATE_TG);
                update_cfs_group(se);
        }

        if (!se)
                sub_nr_running(rq, 1);

        util_est_dequeue(&rq->cfs, p, task_sleep);
        hrtick_update(rq);
}

#ifdef CONFIG_SMP

/* Working cpumask for: load_balance, load_balance_newidle. */
DEFINE_PER_CPU(cpumask_var_t, load_balance_mask);
DEFINE_PER_CPU(cpumask_var_t, select_idle_mask);

#ifdef CONFIG_NO_HZ_COMMON
/*
 * per rq 'load' arrray crap; XXX kill this.
 */

/*
 * The exact cpuload calculated at every tick would be:
 *
 *   load' = (1 - 1/2^i) * load + (1/2^i) * cur_load
 *
 * If a CPU misses updates for n ticks (as it was idle) and update gets
 * called on the n+1-th tick when CPU may be busy, then we have:
 *
 *   load_n   = (1 - 1/2^i)^n * load_0
 *   load_n+1 = (1 - 1/2^i)   * load_n + (1/2^i) * cur_load
 *
 * decay_load_missed() below does efficient calculation of
 *
 *   load' = (1 - 1/2^i)^n * load
 *
 * Because x^(n+m) := x^n * x^m we can decompose any x^n in power-of-2 factors.
 * This allows us to precompute the above in said factors, thereby allowing the
 * reduction of an arbitrary n in O(log_2 n) steps. (See also
 * fixed_power_int())
 *
 * The calculation is approximated on a 128 point scale.
 */
#define DEGRADE_SHIFT           7

static const u8 degrade_zero_ticks[CPU_LOAD_IDX_MAX] = {0, 8, 32, 64, 128};
static const u8 degrade_factor[CPU_LOAD_IDX_MAX][DEGRADE_SHIFT + 1] = {
        {   0,   0,  0,  0,  0,  0, 0, 0 },
        {  64,  32,  8,  0,  0,  0, 0, 0 },
        {  96,  72, 40, 12,  1,  0, 0, 0 },
        { 112,  98, 75, 43, 15,  1, 0, 0 },
        { 120, 112, 98, 76, 45, 16, 2, 0 }
};

/*
 * Update cpu_load for any missed ticks, due to tickless idle. The backlog
 * would be when CPU is idle and so we just decay the old load without
 * adding any new load.
 */
static unsigned long
decay_load_missed(unsigned long load, unsigned long missed_updates, int idx)
{
        int j = 0;

        if (!missed_updates)
                return load;

        if (missed_updates >= degrade_zero_ticks[idx])
                return 0;

        if (idx == 1)
                return load >> missed_updates;

        while (missed_updates) {
                if (missed_updates % 2)
                        load = (load * degrade_factor[idx][j]) >> DEGRADE_SHIFT;

                missed_updates >>= 1;
                j++;
        }
        return load;
}

static struct {
        cpumask_var_t idle_cpus_mask;
        atomic_t nr_cpus;
        int has_blocked;                /* Idle CPUS has blocked load */
        unsigned long next_balance;     /* in jiffy units */
        unsigned long next_blocked;     /* Next update of blocked load in jiffies */
} nohz ____cacheline_aligned;

#endif /* CONFIG_NO_HZ_COMMON */

/**
 * __cpu_load_update - update the rq->cpu_load[] statistics
 * @this_rq: The rq to update statistics for
 * @this_load: The current load
 * @pending_updates: The number of missed updates
 *
 * Update rq->cpu_load[] statistics. This function is usually called every
 * scheduler tick (TICK_NSEC).
 *
 * This function computes a decaying average:
 *
 *   load[i]' = (1 - 1/2^i) * load[i] + (1/2^i) * load
 *
 * Because of NOHZ it might not get called on every tick which gives need for
 * the @pending_updates argument.
 *
 *   load[i]_n = (1 - 1/2^i) * load[i]_n-1 + (1/2^i) * load_n-1
 *             = A * load[i]_n-1 + B ; A := (1 - 1/2^i), B := (1/2^i) * load
 *             = A * (A * load[i]_n-2 + B) + B
 *             = A * (A * (A * load[i]_n-3 + B) + B) + B
 *             = A^3 * load[i]_n-3 + (A^2 + A + 1) * B
 *             = A^n * load[i]_0 + (A^(n-1) + A^(n-2) + ... + 1) * B
 *             = A^n * load[i]_0 + ((1 - A^n) / (1 - A)) * B
 *             = (1 - 1/2^i)^n * (load[i]_0 - load) + load
 *
 * In the above we've assumed load_n := load, which is true for NOHZ_FULL as
 * any change in load would have resulted in the tick being turned back on.
 *
 * For regular NOHZ, this reduces to:
 *
 *   load[i]_n = (1 - 1/2^i)^n * load[i]_0
 *
 * see decay_load_misses(). For NOHZ_FULL we get to subtract and add the extra
 * term.
 */
static void cpu_load_update(struct rq *this_rq, unsigned long this_load,
                            unsigned long pending_updates)
{
        unsigned long __maybe_unused tickless_load = this_rq->cpu_load[0];
        int i, scale;

        this_rq->nr_load_updates++;

        /* Update our load: */
        this_rq->cpu_load[0] = this_load; /* Fasttrack for idx 0 */
        for (i = 1, scale = 2; i < CPU_LOAD_IDX_MAX; i++, scale += scale) {
                unsigned long old_load, new_load;

                /* scale is effectively 1 << i now, and >> i divides by scale */

                old_load = this_rq->cpu_load[i];
#ifdef CONFIG_NO_HZ_COMMON
                old_load = decay_load_missed(old_load, pending_updates - 1, i);
                if (tickless_load) {
                        old_load -= decay_load_missed(tickless_load, pending_updates - 1, i);
                        /*
                         * old_load can never be a negative value because a
                         * decayed tickless_load cannot be greater than the
                         * original tickless_load.
                         */
                        old_load += tickless_load;
                }
#endif
                new_load = this_load;
                /*
                 * Round up the averaging division if load is increasing. This
                 * prevents us from getting stuck on 9 if the load is 10, for
                 * example.
                 */
                if (new_load > old_load)
                        new_load += scale - 1;

                this_rq->cpu_load[i] = (old_load * (scale - 1) + new_load) >> i;
        }
}

/* Used instead of source_load when we know the type == 0 */
static unsigned long weighted_cpuload(struct rq *rq)
{
        return cfs_rq_runnable_load_avg(&rq->cfs);
}

#ifdef CONFIG_NO_HZ_COMMON
/*
 * There is no sane way to deal with nohz on smp when using jiffies because the
 * CPU doing the jiffies update might drift wrt the CPU doing the jiffy reading
 * causing off-by-one errors in observed deltas; {0,2} instead of {1,1}.
 *
 * Therefore we need to avoid the delta approach from the regular tick when
 * possible since that would seriously skew the load calculation. This is why we
 * use cpu_load_update_periodic() for CPUs out of nohz. However we'll rely on
 * jiffies deltas for updates happening while in nohz mode (idle ticks, idle
 * loop exit, nohz_idle_balance, nohz full exit...)
 *
 * This means we might still be one tick off for nohz periods.
 */

static void cpu_load_update_nohz(struct rq *this_rq,
                                 unsigned long curr_jiffies,
                                 unsigned long load)
{
        unsigned long pending_updates;

        pending_updates = curr_jiffies - this_rq->last_load_update_tick;
        if (pending_updates) {
                this_rq->last_load_update_tick = curr_jiffies;
                /*
                 * In the regular NOHZ case, we were idle, this means load 0.
                 * In the NOHZ_FULL case, we were non-idle, we should consider
                 * its weighted load.
                 */
                cpu_load_update(this_rq, load, pending_updates);
        }
}

/*
 * Called from nohz_idle_balance() to update the load ratings before doing the
 * idle balance.
 */
static void cpu_load_update_idle(struct rq *this_rq)
{
        /*
         * bail if there's load or we're actually up-to-date.
         */
        if (weighted_cpuload(this_rq))
                return;

        cpu_load_update_nohz(this_rq, READ_ONCE(jiffies), 0);
}

/*
 * Record CPU load on nohz entry so we know the tickless load to account
 * on nohz exit. cpu_load[0] happens then to be updated more frequently
 * than other cpu_load[idx] but it should be fine as cpu_load readers
 * shouldn't rely into synchronized cpu_load[*] updates.
 */
void cpu_load_update_nohz_start(void)
{
        struct rq *this_rq = this_rq();

        /*
         * This is all lockless but should be fine. If weighted_cpuload changes
         * concurrently we'll exit nohz. And cpu_load write can race with
         * cpu_load_update_idle() but both updater would be writing the same.
         */
        this_rq->cpu_load[0] = weighted_cpuload(this_rq);
}

/*
 * Account the tickless load in the end of a nohz frame.
 */
void cpu_load_update_nohz_stop(void)
{
        unsigned long curr_jiffies = READ_ONCE(jiffies);
        struct rq *this_rq = this_rq();
        unsigned long load;
        struct rq_flags rf;

        if (curr_jiffies == this_rq->last_load_update_tick)
                return;

        load = weighted_cpuload(this_rq);
        rq_lock(this_rq, &rf);
        update_rq_clock(this_rq);
        cpu_load_update_nohz(this_rq, curr_jiffies, load);
        rq_unlock(this_rq, &rf);
}
#else /* !CONFIG_NO_HZ_COMMON */
static inline void cpu_load_update_nohz(struct rq *this_rq,
                                        unsigned long curr_jiffies,
                                        unsigned long load) { }
#endif /* CONFIG_NO_HZ_COMMON */

static void cpu_load_update_periodic(struct rq *this_rq, unsigned long load)
{
#ifdef CONFIG_NO_HZ_COMMON
        /* See the mess around cpu_load_update_nohz(). */
        this_rq->last_load_update_tick = READ_ONCE(jiffies);
#endif
        cpu_load_update(this_rq, load, 1);
}

/*
 * Called from scheduler_tick()
 */
void cpu_load_update_active(struct rq *this_rq)
{
        unsigned long load = weighted_cpuload(this_rq);

        if (tick_nohz_tick_stopped())
                cpu_load_update_nohz(this_rq, READ_ONCE(jiffies), load);
        else
                cpu_load_update_periodic(this_rq, load);
}

/*
 * Return a low guess at the load of a migration-source CPU weighted
 * according to the scheduling class and "nice" value.
 *
 * We want to under-estimate the load of migration sources, to
 * balance conservatively.
 */
static unsigned long source_load(int cpu, int type)
{
        struct rq *rq = cpu_rq(cpu);
        unsigned long total = weighted_cpuload(rq);

        if (type == 0 || !sched_feat(LB_BIAS))
                return total;

        return min(rq->cpu_load[type-1], total);
}

/*
 * Return a high guess at the load of a migration-target CPU weighted
 * according to the scheduling class and "nice" value.
 */
static unsigned long target_load(int cpu, int type)
{
        struct rq *rq = cpu_rq(cpu);
        unsigned long total = weighted_cpuload(rq);

        if (type == 0 || !sched_feat(LB_BIAS))
                return total;

        return max(rq->cpu_load[type-1], total);
}

static unsigned long capacity_of(int cpu)
{
        return cpu_rq(cpu)->cpu_capacity;
}

static unsigned long capacity_orig_of(int cpu)
{
        return cpu_rq(cpu)->cpu_capacity_orig;
}

static unsigned long cpu_avg_load_per_task(int cpu)
{
        struct rq *rq = cpu_rq(cpu);
        unsigned long nr_running = READ_ONCE(rq->cfs.h_nr_running);
        unsigned long load_avg = weighted_cpuload(rq);

        if (nr_running)
                return load_avg / nr_running;

        return 0;
}

static void record_wakee(struct task_struct *p)
{
        /*
         * Only decay a single time; tasks that have less then 1 wakeup per
         * jiffy will not have built up many flips.
         */
        if (time_after(jiffies, current->wakee_flip_decay_ts + HZ)) {
                current->wakee_flips >>= 1;
                current->wakee_flip_decay_ts = jiffies;
        }

        if (current->last_wakee != p) {
                current->last_wakee = p;
                current->wakee_flips++;
        }
}

/*
 * Detect M:N waker/wakee relationships via a switching-frequency heuristic.
 *
 * A waker of many should wake a different task than the one last awakened
 * at a frequency roughly N times higher than one of its wakees.
 *
 * In order to determine whether we should let the load spread vs consolidating
 * to shared cache, we look for a minimum 'flip' frequency of llc_size in one
 * partner, and a factor of lls_size higher frequency in the other.
 *
 * With both conditions met, we can be relatively sure that the relationship is
 * non-monogamous, with partner count exceeding socket size.
 *
 * Waker/wakee being client/server, worker/dispatcher, interrupt source or
 * whatever is irrelevant, spread criteria is apparent partner count exceeds
 * socket size.
 */
static int wake_wide(struct task_struct *p)
{
        unsigned int master = current->wakee_flips;
        unsigned int slave = p->wakee_flips;
        int factor = this_cpu_read(sd_llc_size);

        if (master < slave)
                swap(master, slave);
        if (slave < factor || master < slave * factor)
                return 0;
        return 1;
}

/*
 * The purpose of wake_affine() is to quickly determine on which CPU we can run
 * soonest. For the purpose of speed we only consider the waking and previous
 * CPU.
 *
 * wake_affine_idle() - only considers 'now', it check if the waking CPU is
 *                      cache-affine and is (or will be) idle.
 *
 * wake_affine_weight() - considers the weight to reflect the average
 *                        scheduling latency of the CPUs. This seems to work
 *                        for the overloaded case.
 */
static int
wake_affine_idle(int this_cpu, int prev_cpu, int sync)
{
        /*
         * If this_cpu is idle, it implies the wakeup is from interrupt
         * context. Only allow the move if cache is shared. Otherwise an
         * interrupt intensive workload could force all tasks onto one
         * node depending on the IO topology or IRQ affinity settings.
         *
         * If the prev_cpu is idle and cache affine then avoid a migration.
         * There is no guarantee that the cache hot data from an interrupt
         * is more important than cache hot data on the prev_cpu and from
         * a cpufreq perspective, it's better to have higher utilisation
         * on one CPU.
         */
        if (available_idle_cpu(this_cpu) && cpus_share_cache(this_cpu, prev_cpu))
                return available_idle_cpu(prev_cpu) ? prev_cpu : this_cpu;

        if (sync && cpu_rq(this_cpu)->nr_running == 1)
                return this_cpu;

        return nr_cpumask_bits;
}

static int
wake_affine_weight(struct sched_domain *sd, struct task_struct *p,
                   int this_cpu, int prev_cpu, int sync)
{
        s64 this_eff_load, prev_eff_load;
        unsigned long task_load;

        this_eff_load = target_load(this_cpu, sd->wake_idx);

        if (sync) {
                unsigned long current_load = task_h_load(current);

                if (current_load > this_eff_load)
                        return this_cpu;

                this_eff_load -= current_load;
        }

        task_load = task_h_load(p);

        this_eff_load += task_load;
        if (sched_feat(WA_BIAS))
                this_eff_load *= 100;
        this_eff_load *= capacity_of(prev_cpu);

        prev_eff_load = source_load(prev_cpu, sd->wake_idx);
        prev_eff_load -= task_load;
        if (sched_feat(WA_BIAS))
                prev_eff_load *= 100 + (sd->imbalance_pct - 100) / 2;
        prev_eff_load *= capacity_of(this_cpu);

        /*
         * If sync, adjust the weight of prev_eff_load such that if
         * prev_eff == this_eff that select_idle_sibling() will consider
         * stacking the wakee on top of the waker if no other CPU is
         * idle.
         */
        if (sync)
                prev_eff_load += 1;

        return this_eff_load < prev_eff_load ? this_cpu : nr_cpumask_bits;
}

static int wake_affine(struct sched_domain *sd, struct task_struct *p,
                       int this_cpu, int prev_cpu, int sync)
{
        int target = nr_cpumask_bits;

        if (sched_feat(WA_IDLE))
                target = wake_affine_idle(this_cpu, prev_cpu, sync);

        if (sched_feat(WA_WEIGHT) && target == nr_cpumask_bits)
                target = wake_affine_weight(sd, p, this_cpu, prev_cpu, sync);

        schedstat_inc(p->se.statistics.nr_wakeups_affine_attempts);
        if (target == nr_cpumask_bits)
                return prev_cpu;

        schedstat_inc(sd->ttwu_move_affine);
        schedstat_inc(p->se.statistics.nr_wakeups_affine);
        return target;
}

static unsigned long cpu_util_wake(int cpu, struct task_struct *p);

static unsigned long capacity_spare_wake(int cpu, struct task_struct *p)
{
        return max_t(long, capacity_of(cpu) - cpu_util_wake(cpu, p), 0);
}

/*
 * find_idlest_group finds and returns the least busy CPU group within the
 * domain.
 *
 * Assumes p is allowed on at least one CPU in sd.
 */
static struct sched_group *
find_idlest_group(struct sched_domain *sd, struct task_struct *p,
                  int this_cpu, int sd_flag)
{
        struct sched_group *idlest = NULL, *group = sd->groups;
        struct sched_group *most_spare_sg = NULL;
        unsigned long min_runnable_load = ULONG_MAX;
        unsigned long this_runnable_load = ULONG_MAX;
        unsigned long min_avg_load = ULONG_MAX, this_avg_load = ULONG_MAX;
        unsigned long most_spare = 0, this_spare = 0;
        int load_idx = sd->forkexec_idx;
        int imbalance_scale = 100 + (sd->imbalance_pct-100)/2;
        unsigned long imbalance = scale_load_down(NICE_0_LOAD) *
                                (sd->imbalance_pct-100) / 100;

        if (sd_flag & SD_BALANCE_WAKE)
                load_idx = sd->wake_idx;

        do {
                unsigned long load, avg_load, runnable_load;
                unsigned long spare_cap, max_spare_cap;
                int local_group;
                int i;

                /* Skip over this group if it has no CPUs allowed */
                if (!cpumask_intersects(sched_group_span(group),
                                        &p->cpus_allowed))
                        continue;

                local_group = cpumask_test_cpu(this_cpu,
                                               sched_group_span(group));

                /*
                 * Tally up the load of all CPUs in the group and find
                 * the group containing the CPU with most spare capacity.
                 */
                avg_load = 0;
                runnable_load = 0;
                max_spare_cap = 0;

                for_each_cpu(i, sched_group_span(group)) {
                        /* Bias balancing toward CPUs of our domain */
                        if (local_group)
                                load = source_load(i, load_idx);
                        else
                                load = target_load(i, load_idx);

                        runnable_load += load;

                        avg_load += cfs_rq_load_avg(&cpu_rq(i)->cfs);

                        spare_cap = capacity_spare_wake(i, p);

                        if (spare_cap > max_spare_cap)
                                max_spare_cap = spare_cap;
                }

                /* Adjust by relative CPU capacity of the group */
                avg_load = (avg_load * SCHED_CAPACITY_SCALE) /
                                        group->sgc->capacity;
                runnable_load = (runnable_load * SCHED_CAPACITY_SCALE) /
                                        group->sgc->capacity;

                if (local_group) {
                        this_runnable_load = runnable_load;
                        this_avg_load = avg_load;
                        this_spare = max_spare_cap;
                } else {
                        if (min_runnable_load > (runnable_load + imbalance)) {
                                /*
                                 * The runnable load is significantly smaller
                                 * so we can pick this new CPU:
                                 */
                                min_runnable_load = runnable_load;
                                min_avg_load = avg_load;
                                idlest = group;
                        } else if ((runnable_load < (min_runnable_load + imbalance)) &&
                                   (100*min_avg_load > imbalance_scale*avg_load)) {
                                /*
                                 * The runnable loads are close so take the
                                 * blocked load into account through avg_load:
                                 */
                                min_avg_load = avg_load;
                                idlest = group;
                        }

                        if (most_spare < max_spare_cap) {
                                most_spare = max_spare_cap;
                                most_spare_sg = group;
                        }
                }
        } while (group = group->next, group != sd->groups);

        /*
         * The cross-over point between using spare capacity or least load
         * is too conservative for high utilization tasks on partially
         * utilized systems if we require spare_capacity > task_util(p),
         * so we allow for some task stuffing by using
         * spare_capacity > task_util(p)/2.
         *
         * Spare capacity can't be used for fork because the utilization has
         * not been set yet, we must first select a rq to compute the initial
         * utilization.
         */
        if (sd_flag & SD_BALANCE_FORK)
                goto skip_spare;

        if (this_spare > task_util(p) / 2 &&
            imbalance_scale*this_spare > 100*most_spare)
                return NULL;

        if (most_spare > task_util(p) / 2)
                return most_spare_sg;

skip_spare:
        if (!idlest)
                return NULL;

        /*
         * When comparing groups across NUMA domains, it's possible for the
         * local domain to be very lightly loaded relative to the remote
         * domains but "imbalance" skews the comparison making remote CPUs
         * look much more favourable. When considering cross-domain, add
         * imbalance to the runnable load on the remote node and consider
         * staying local.
         */
        if ((sd->flags & SD_NUMA) &&
            min_runnable_load + imbalance >= this_runnable_load)
                return NULL;

        if (min_runnable_load > (this_runnable_load + imbalance))
                return NULL;

        if ((this_runnable_load < (min_runnable_load + imbalance)) &&
             (100*this_avg_load < imbalance_scale*min_avg_load))
                return NULL;

        return idlest;
}

/*
 * find_idlest_group_cpu - find the idlest CPU among the CPUs in the group.
 */
static int
find_idlest_group_cpu(struct sched_group *group, struct task_struct *p, int this_cpu)
{
        unsigned long load, min_load = ULONG_MAX;
        unsigned int min_exit_latency = UINT_MAX;
        u64 latest_idle_timestamp = 0;
        int least_loaded_cpu = this_cpu;
        int shallowest_idle_cpu = -1;
        int i;

        /* Check if we have any choice: */
        if (group->group_weight == 1)
                return cpumask_first(sched_group_span(group));

        /* Traverse only the allowed CPUs */
        for_each_cpu_and(i, sched_group_span(group), &p->cpus_allowed) {
                if (available_idle_cpu(i)) {
                        struct rq *rq = cpu_rq(i);
                        struct cpuidle_state *idle = idle_get_state(rq);
                        if (idle && idle->exit_latency < min_exit_latency) {
                                /*
                                 * We give priority to a CPU whose idle state
                                 * has the smallest exit latency irrespective
                                 * of any idle timestamp.
                                 */
                                min_exit_latency = idle->exit_latency;
                                latest_idle_timestamp = rq->idle_stamp;
                                shallowest_idle_cpu = i;
                        } else if ((!idle || idle->exit_latency == min_exit_latency) &&
                                   rq->idle_stamp > latest_idle_timestamp) {
                                /*
                                 * If equal or no active idle state, then
                                 * the most recently idled CPU might have
                                 * a warmer cache.
                                 */
                                latest_idle_timestamp = rq->idle_stamp;
                                shallowest_idle_cpu = i;
                        }
                } else if (shallowest_idle_cpu == -1) {
                        load = weighted_cpuload(cpu_rq(i));
                        if (load < min_load) {
                                min_load = load;
                                least_loaded_cpu = i;
                        }
                }
        }

        return shallowest_idle_cpu != -1 ? shallowest_idle_cpu : least_loaded_cpu;
}

static inline int find_idlest_cpu(struct sched_domain *sd, struct task_struct *p,
                                  int cpu, int prev_cpu, int sd_flag)
{
        int new_cpu = cpu;

        if (!cpumask_intersects(sched_domain_span(sd), &p->cpus_allowed))
                return prev_cpu;

        /*
         * We need task's util for capacity_spare_wake, sync it up to prev_cpu's
         * last_update_time.
         */
        if (!(sd_flag & SD_BALANCE_FORK))
                sync_entity_load_avg(&p->se);

        while (sd) {
                struct sched_group *group;
                struct sched_domain *tmp;
                int weight;

                if (!(sd->flags & sd_flag)) {
                        sd = sd->child;
                        continue;
                }

                group = find_idlest_group(sd, p, cpu, sd_flag);
                if (!group) {
                        sd = sd->child;
                        continue;
                }

                new_cpu = find_idlest_group_cpu(group, p, cpu);
                if (new_cpu == cpu) {
                        /* Now try balancing at a lower domain level of 'cpu': */
                        sd = sd->child;
                        continue;
                }

                /* Now try balancing at a lower domain level of 'new_cpu': */
                cpu = new_cpu;
                weight = sd->span_weight;
                sd = NULL;
                for_each_domain(cpu, tmp) {
                        if (weight <= tmp->span_weight)
                                break;
                        if (tmp->flags & sd_flag)
                                sd = tmp;
                }
        }

        return new_cpu;
}

#ifdef CONFIG_SCHED_SMT
DEFINE_STATIC_KEY_FALSE(sched_smt_present);

static inline void set_idle_cores(int cpu, int val)
{
        struct sched_domain_shared *sds;

        sds = rcu_dereference(per_cpu(sd_llc_shared, cpu));
        if (sds)
                WRITE_ONCE(sds->has_idle_cores, val);
}

static inline bool test_idle_cores(int cpu, bool def)
{
        struct sched_domain_shared *sds;

        sds = rcu_dereference(per_cpu(sd_llc_shared, cpu));
        if (sds)
                return READ_ONCE(sds->has_idle_cores);

        return def;
}

/*
 * Scans the local SMT mask to see if the entire core is idle, and records this
 * information in sd_llc_shared->has_idle_cores.
 *
 * Since SMT siblings share all cache levels, inspecting this limited remote
 * state should be fairly cheap.
 */
void __update_idle_core(struct rq *rq)
{
        int core = cpu_of(rq);
        int cpu;

        rcu_read_lock();
        if (test_idle_cores(core, true))
                goto unlock;

        for_each_cpu(cpu, cpu_smt_mask(core)) {
                if (cpu == core)
                        continue;

                if (!available_idle_cpu(cpu))
                        goto unlock;
        }

        set_idle_cores(core, 1);
unlock:
        rcu_read_unlock();
}

/*
 * Scan the entire LLC domain for idle cores; this dynamically switches off if
 * there are no idle cores left in the system; tracked through
 * sd_llc->shared->has_idle_cores and enabled through update_idle_core() above.
 */
static int select_idle_core(struct task_struct *p, struct sched_domain *sd, int target)
{
        struct cpumask *cpus = this_cpu_cpumask_var_ptr(select_idle_mask);
        int core, cpu;

        if (!static_branch_likely(&sched_smt_present))
                return -1;

        if (!test_idle_cores(target, false))
                return -1;

        cpumask_and(cpus, sched_domain_span(sd), &p->cpus_allowed);

        for_each_cpu_wrap(core, cpus, target) {
                bool idle = true;

                for_each_cpu(cpu, cpu_smt_mask(core)) {
                        cpumask_clear_cpu(cpu, cpus);
                        if (!available_idle_cpu(cpu))
                                idle = false;
                }

                if (idle)
                        return core;
        }

        /*
         * Failed to find an idle core; stop looking for one.
         */
        set_idle_cores(target, 0);

        return -1;
}

/*
 * Scan the local SMT mask for idle CPUs.
 */
static int select_idle_smt(struct task_struct *p, struct sched_domain *sd, int target)
{
        int cpu;

        if (!static_branch_likely(&sched_smt_present))
                return -1;

        for_each_cpu(cpu, cpu_smt_mask(target)) {
                if (!cpumask_test_cpu(cpu, &p->cpus_allowed))
                        continue;
                if (available_idle_cpu(cpu))
                        return cpu;
        }

        return -1;
}

#else /* CONFIG_SCHED_SMT */

static inline int select_idle_core(struct task_struct *p, struct sched_domain *sd, int target)
{
        return -1;
}

static inline int select_idle_smt(struct task_struct *p, struct sched_domain *sd, int target)
{
        return -1;
}

#endif /* CONFIG_SCHED_SMT */

/*
 * Scan the LLC domain for idle CPUs; this is dynamically regulated by
 * comparing the average scan cost (tracked in sd->avg_scan_cost) against the
 * average idle time for this rq (as found in rq->avg_idle).
 */
static int select_idle_cpu(struct task_struct *p, struct sched_domain *sd, int target)
{
        struct sched_domain *this_sd;
        u64 avg_cost, avg_idle;
        u64 time, cost;
        s64 delta;
        int cpu, nr = INT_MAX;

        this_sd = rcu_dereference(*this_cpu_ptr(&sd_llc));
        if (!this_sd)
                return -1;

        /*
         * Due to large variance we need a large fuzz factor; hackbench in
         * particularly is sensitive here.
         */
        avg_idle = this_rq()->avg_idle / 512;
        avg_cost = this_sd->avg_scan_cost + 1;

        if (sched_feat(SIS_AVG_CPU) && avg_idle < avg_cost)
                return -1;

        if (sched_feat(SIS_PROP)) {
                u64 span_avg = sd->span_weight * avg_idle;
                if (span_avg > 4*avg_cost)
                        nr = div_u64(span_avg, avg_cost);
                else
                        nr = 4;
        }

        time = local_clock();

        for_each_cpu_wrap(cpu, sched_domain_span(sd), target) {
                if (!--nr)
                        return -1;
                if (!cpumask_test_cpu(cpu, &p->cpus_allowed))
                        continue;
                if (available_idle_cpu(cpu))
                        break;
        }

        time = local_clock() - time;
        cost = this_sd->avg_scan_cost;
        delta = (s64)(time - cost) / 8;
        this_sd->avg_scan_cost += delta;

        return cpu;
}

/*
 * Try and locate an idle core/thread in the LLC cache domain.
 */
static int select_idle_sibling(struct task_struct *p, int prev, int target)
{
        struct sched_domain *sd;
        int i, recent_used_cpu;

        if (available_idle_cpu(target))
                return target;

        /*
         * If the previous CPU is cache affine and idle, don't be stupid:
         */
        if (prev != target && cpus_share_cache(prev, target) && available_idle_cpu(prev))
                return prev;

        /* Check a recently used CPU as a potential idle candidate: */
        recent_used_cpu = p->recent_used_cpu;
        if (recent_used_cpu != prev &&
            recent_used_cpu != target &&
            cpus_share_cache(recent_used_cpu, target) &&
            available_idle_cpu(recent_used_cpu) &&
            cpumask_test_cpu(p->recent_used_cpu, &p->cpus_allowed)) {
                /*
                 * Replace recent_used_cpu with prev as it is a potential
                 * candidate for the next wake:
                 */
                p->recent_used_cpu = prev;
                return recent_used_cpu;
        }

        sd = rcu_dereference(per_cpu(sd_llc, target));
        if (!sd)
                return target;

        i = select_idle_core(p, sd, target);
        if ((unsigned)i < nr_cpumask_bits)
                return i;

        i = select_idle_cpu(p, sd, target);
        if ((unsigned)i < nr_cpumask_bits)
                return i;

        i = select_idle_smt(p, sd, target);
        if ((unsigned)i < nr_cpumask_bits)
                return i;

        return target;
}

/**
 * Amount of capacity of a CPU that is (estimated to be) used by CFS tasks
 * @cpu: the CPU to get the utilization of
 *
 * The unit of the return value must be the one of capacity so we can compare
 * the utilization with the capacity of the CPU that is available for CFS task
 * (ie cpu_capacity).
 *
 * cfs_rq.avg.util_avg is the sum of running time of runnable tasks plus the
 * recent utilization of currently non-runnable tasks on a CPU. It represents
 * the amount of utilization of a CPU in the range [0..capacity_orig] where
 * capacity_orig is the cpu_capacity available at the highest frequency
 * (arch_scale_freq_capacity()).
 * The utilization of a CPU converges towards a sum equal to or less than the
 * current capacity (capacity_curr <= capacity_orig) of the CPU because it is
 * the running time on this CPU scaled by capacity_curr.
 *
 * The estimated utilization of a CPU is defined to be the maximum between its
 * cfs_rq.avg.util_avg and the sum of the estimated utilization of the tasks
 * currently RUNNABLE on that CPU.
 * This allows to properly represent the expected utilization of a CPU which
 * has just got a big task running since a long sleep period. At the same time
 * however it preserves the benefits of the "blocked utilization" in
 * describing the potential for other tasks waking up on the same CPU.
 *
 * Nevertheless, cfs_rq.avg.util_avg can be higher than capacity_curr or even
 * higher than capacity_orig because of unfortunate rounding in
 * cfs.avg.util_avg or just after migrating tasks and new task wakeups until
 * the average stabilizes with the new running time. We need to check that the
 * utilization stays within the range of [0..capacity_orig] and cap it if
 * necessary. Without utilization capping, a group could be seen as overloaded
 * (CPU0 utilization at 121% + CPU1 utilization at 80%) whereas CPU1 has 20% of
 * available capacity. We allow utilization to overshoot capacity_curr (but not
 * capacity_orig) as it useful for predicting the capacity required after task
 * migrations (scheduler-driven DVFS).
 *
 * Return: the (estimated) utilization for the specified CPU
 */
static inline unsigned long cpu_util(int cpu)
{
        struct cfs_rq *cfs_rq;
        unsigned int util;

        cfs_rq = &cpu_rq(cpu)->cfs;
        util = READ_ONCE(cfs_rq->avg.util_avg);

        if (sched_feat(UTIL_EST))
                util = max(util, READ_ONCE(cfs_rq->avg.util_est.enqueued));

        return min_t(unsigned long, util, capacity_orig_of(cpu));
}

/*
 * cpu_util_wake: Compute CPU utilization with any contributions from
 * the waking task p removed.
 */
static unsigned long cpu_util_wake(int cpu, struct task_struct *p)
{
        struct cfs_rq *cfs_rq;
        unsigned int util;

        /* Task has no contribution or is new */
        if (cpu != task_cpu(p) || !READ_ONCE(p->se.avg.last_update_time))
                return cpu_util(cpu);

        cfs_rq = &cpu_rq(cpu)->cfs;
        util = READ_ONCE(cfs_rq->avg.util_avg);

        /* Discount task's blocked util from CPU's util */
        util -= min_t(unsigned int, util, task_util(p));

        /*
         * Covered cases:
         *
         * a) if *p is the only task sleeping on this CPU, then:
         *      cpu_util (== task_util) > util_est (== 0)
         *    and thus we return:
         *      cpu_util_wake = (cpu_util - task_util) = 0
         *
         * b) if other tasks are SLEEPING on this CPU, which is now exiting
         *    IDLE, then:
         *      cpu_util >= task_util
         *      cpu_util > util_est (== 0)
         *    and thus we discount *p's blocked utilization to return:
         *      cpu_util_wake = (cpu_util - task_util) >= 0
         *
         * c) if other tasks are RUNNABLE on that CPU and
         *      util_est > cpu_util
         *    then we use util_est since it returns a more restrictive
         *    estimation of the spare capacity on that CPU, by just
         *    considering the expected utilization of tasks already
         *    runnable on that CPU.
         *
         * Cases a) and b) are covered by the above code, while case c) is
         * covered by the following code when estimated utilization is
         * enabled.
         */
        if (sched_feat(UTIL_EST))
                util = max(util, READ_ONCE(cfs_rq->avg.util_est.enqueued));

        /*
         * Utilization (estimated) can exceed the CPU capacity, thus let's
         * clamp to the maximum CPU capacity to ensure consistency with
         * the cpu_util call.
         */
        return min_t(unsigned long, util, capacity_orig_of(cpu));
}

/*
 * Disable WAKE_AFFINE in the case where task @p doesn't fit in the
 * capacity of either the waking CPU @cpu or the previous CPU @prev_cpu.
 *
 * In that case WAKE_AFFINE doesn't make sense and we'll let
 * BALANCE_WAKE sort things out.
 */
static int wake_cap(struct task_struct *p, int cpu, int prev_cpu)
{
        long min_cap, max_cap;

        min_cap = min(capacity_orig_of(prev_cpu), capacity_orig_of(cpu));
        max_cap = cpu_rq(cpu)->rd->max_cpu_capacity;

        /* Minimum capacity is close to max, no need to abort wake_affine */
        if (max_cap - min_cap < max_cap >> 3)
                return 0;

        /* Bring task utilization in sync with prev_cpu */
        sync_entity_load_avg(&p->se);

        return min_cap * 1024 < task_util(p) * capacity_margin;
}

/*
 * select_task_rq_fair: Select target runqueue for the waking task in domains
 * that have the 'sd_flag' flag set. In practice, this is SD_BALANCE_WAKE,
 * SD_BALANCE_FORK, or SD_BALANCE_EXEC.
 *
 * Balances load by selecting the idlest CPU in the idlest group, or under
 * certain conditions an idle sibling CPU if the domain has SD_WAKE_AFFINE set.
 *
 * Returns the target CPU number.
 *
 * preempt must be disabled.
 */
static int
select_task_rq_fair(struct task_struct *p, int prev_cpu, int sd_flag, int wake_flags)
{
        struct sched_domain *tmp, *sd = NULL;
        int cpu = smp_processor_id();
        int new_cpu = prev_cpu;
        int want_affine = 0;
        int sync = (wake_flags & WF_SYNC) && !(current->flags & PF_EXITING);

        if (sd_flag & SD_BALANCE_WAKE) {
                record_wakee(p);
                want_affine = !wake_wide(p) && !wake_cap(p, cpu, prev_cpu)
                              && cpumask_test_cpu(cpu, &p->cpus_allowed);
        }

        rcu_read_lock();
        for_each_domain(cpu, tmp) {
                if (!(tmp->flags & SD_LOAD_BALANCE))
                        break;

                /*
                 * If both 'cpu' and 'prev_cpu' are part of this domain,
                 * cpu is a valid SD_WAKE_AFFINE target.
                 */
                if (want_affine && (tmp->flags & SD_WAKE_AFFINE) &&
                    cpumask_test_cpu(prev_cpu, sched_domain_span(tmp))) {
                        if (cpu != prev_cpu)
                                new_cpu = wake_affine(tmp, p, cpu, prev_cpu, sync);

                        sd = NULL; /* Prefer wake_affine over balance flags */
                        break;
                }

                if (tmp->flags & sd_flag)
                        sd = tmp;
                else if (!want_affine)
                        break;
        }

        if (unlikely(sd)) {
                /* Slow path */
                new_cpu = find_idlest_cpu(sd, p, cpu, prev_cpu, sd_flag);
        } else if (sd_flag & SD_BALANCE_WAKE) { /* XXX always ? */
                /* Fast path */

                new_cpu = select_idle_sibling(p, prev_cpu, new_cpu);

                if (want_affine)
                        current->recent_used_cpu = cpu;
        }
        rcu_read_unlock();

        return new_cpu;
}

static void detach_entity_cfs_rq(struct sched_entity *se);

/*
 * Called immediately before a task is migrated to a new CPU; task_cpu(p) and
 * cfs_rq_of(p) references at time of call are still valid and identify the
 * previous CPU. The caller guarantees p->pi_lock or task_rq(p)->lock is held.
 */
static void migrate_task_rq_fair(struct task_struct *p)
{
        /*
         * As blocked tasks retain absolute vruntime the migration needs to
         * deal with this by subtracting the old and adding the new
         * min_vruntime -- the latter is done by enqueue_entity() when placing
         * the task on the new runqueue.
         */
        if (p->state == TASK_WAKING) {
                struct sched_entity *se = &p->se;
                struct cfs_rq *cfs_rq = cfs_rq_of(se);
                u64 min_vruntime;

#ifndef CONFIG_64BIT
                u64 min_vruntime_copy;

                do {
                        min_vruntime_copy = cfs_rq->min_vruntime_copy;
                        smp_rmb();
                        min_vruntime = cfs_rq->min_vruntime;
                } while (min_vruntime != min_vruntime_copy);
#else
                min_vruntime = cfs_rq->min_vruntime;
#endif

                se->vruntime -= min_vruntime;
        }

        if (p->on_rq == TASK_ON_RQ_MIGRATING) {
                /*
                 * In case of TASK_ON_RQ_MIGRATING we in fact hold the 'old'
                 * rq->lock and can modify state directly.
                 */
                lockdep_assert_held(&task_rq(p)->lock);
                detach_entity_cfs_rq(&p->se);

        } else {
                /*
                 * We are supposed to update the task to "current" time, then
                 * its up to date and ready to go to new CPU/cfs_rq. But we
                 * have difficulty in getting what current time is, so simply
                 * throw away the out-of-date time. This will result in the
                 * wakee task is less decayed, but giving the wakee more load
                 * sounds not bad.
                 */
                remove_entity_load_avg(&p->se);
        }

        /* Tell new CPU we are migrated */
        p->se.avg.last_update_time = 0;

        /* We have migrated, no longer consider this task hot */
        p->se.exec_start = 0;
}

static void task_dead_fair(struct task_struct *p)
{
        remove_entity_load_avg(&p->se);
}
#endif /* CONFIG_SMP */

static unsigned long wakeup_gran(struct sched_entity *se)
{
        unsigned long gran = sysctl_sched_wakeup_granularity;

        /*
         * Since its curr running now, convert the gran from real-time
         * to virtual-time in his units.
         *
         * By using 'se' instead of 'curr' we penalize light tasks, so
         * they get preempted easier. That is, if 'se' < 'curr' then
         * the resulting gran will be larger, therefore penalizing the
         * lighter, if otoh 'se' > 'curr' then the resulting gran will
         * be smaller, again penalizing the lighter task.
         *
         * This is especially important for buddies when the leftmost
         * task is higher priority than the buddy.
         */
        return calc_delta_fair(gran, se);
}

/*
 * Should 'se' preempt 'curr'.
 *
 *             |s1
 *        |s2
 *   |s3
 *         g
 *      |<--->|c
 *
 *  w(c, s1) = -1
 *  w(c, s2) =  0
 *  w(c, s3) =  1
 *
 */
static int
wakeup_preempt_entity(struct sched_entity *curr, struct sched_entity *se)
{
        s64 gran, vdiff = curr->vruntime - se->vruntime;

        if (vdiff <= 0)
                return -1;

        gran = wakeup_gran(se);
        if (vdiff > gran)
                return 1;

        return 0;
}

static void set_last_buddy(struct sched_entity *se)
{
        if (entity_is_task(se) && unlikely(task_of(se)->policy == SCHED_IDLE))
                return;

        for_each_sched_entity(se) {
                if (SCHED_WARN_ON(!se->on_rq))
                        return;
                cfs_rq_of(se)->last = se;
        }
}

static void set_next_buddy(struct sched_entity *se)
{
        if (entity_is_task(se) && unlikely(task_of(se)->policy == SCHED_IDLE))
                return;

        for_each_sched_entity(se) {
                if (SCHED_WARN_ON(!se->on_rq))
                        return;
                cfs_rq_of(se)->next = se;
        }
}

static void set_skip_buddy(struct sched_entity *se)
{
        for_each_sched_entity(se)
                cfs_rq_of(se)->skip = se;
}

/*
 * Preempt the current task with a newly woken task if needed:
 */
static void check_preempt_wakeup(struct rq *rq, struct task_struct *p, int wake_flags)
{
        struct task_struct *curr = rq->curr;
        struct sched_entity *se = &curr->se, *pse = &p->se;
        struct cfs_rq *cfs_rq = task_cfs_rq(curr);
        int scale = cfs_rq->nr_running >= sched_nr_latency;
        int next_buddy_marked = 0;

        if (unlikely(se == pse))
                return;

        /*
         * This is possible from callers such as attach_tasks(), in which we
         * unconditionally check_prempt_curr() after an enqueue (which may have
         * lead to a throttle).  This both saves work and prevents false
         * next-buddy nomination below.
         */
        if (unlikely(throttled_hierarchy(cfs_rq_of(pse))))
                return;

        if (sched_feat(NEXT_BUDDY) && scale && !(wake_flags & WF_FORK)) {
                set_next_buddy(pse);
                next_buddy_marked = 1;
        }

        /*
         * We can come here with TIF_NEED_RESCHED already set from new task
         * wake up path.
         *
         * Note: this also catches the edge-case of curr being in a throttled
         * group (e.g. via set_curr_task), since update_curr() (in the
         * enqueue of curr) will have resulted in resched being set.  This
         * prevents us from potentially nominating it as a false LAST_BUDDY
         * below.
         */
        if (test_tsk_need_resched(curr))
                return;

        /* Idle tasks are by definition preempted by non-idle tasks. */
        if (unlikely(curr->policy == SCHED_IDLE) &&
            likely(p->policy != SCHED_IDLE))
                goto preempt;

        /*
         * Batch and idle tasks do not preempt non-idle tasks (their preemption
         * is driven by the tick):
         */
        if (unlikely(p->policy != SCHED_NORMAL) || !sched_feat(WAKEUP_PREEMPTION))
                return;

        find_matching_se(&se, &pse);
        update_curr(cfs_rq_of(se));
        BUG_ON(!pse);
        if (wakeup_preempt_entity(se, pse) == 1) {
                /*
                 * Bias pick_next to pick the sched entity that is
                 * triggering this preemption.
                 */
                if (!next_buddy_marked)
                        set_next_buddy(pse);
                goto preempt;
        }

        return;

preempt:
        resched_curr(rq);
        /*
         * Only set the backward buddy when the current task is still
         * on the rq. This can happen when a wakeup gets interleaved
         * with schedule on the ->pre_schedule() or idle_balance()
         * point, either of which can * drop the rq lock.
         *
         * Also, during early boot the idle thread is in the fair class,
         * for obvious reasons its a bad idea to schedule back to it.
         */
        if (unlikely(!se->on_rq || curr == rq->idle))
                return;

        if (sched_feat(LAST_BUDDY) && scale && entity_is_task(se))
                set_last_buddy(se);
}

static struct task_struct *
pick_next_task_fair(struct rq *rq, struct task_struct *prev, struct rq_flags *rf)
{
        struct cfs_rq *cfs_rq = &rq->cfs;
        struct sched_entity *se;
        struct task_struct *p;
        int new_tasks;

again:
        if (!cfs_rq->nr_running)
                goto idle;

#ifdef CONFIG_FAIR_GROUP_SCHED
        if (prev->sched_class != &fair_sched_class)
                goto simple;

        /*
         * Because of the set_next_buddy() in dequeue_task_fair() it is rather
         * likely that a next task is from the same cgroup as the current.
         *
         * Therefore attempt to avoid putting and setting the entire cgroup
         * hierarchy, only change the part that actually changes.
         */

        do {
                struct sched_entity *curr = cfs_rq->curr;

                /*
                 * Since we got here without doing put_prev_entity() we also
                 * have to consider cfs_rq->curr. If it is still a runnable
                 * entity, update_curr() will update its vruntime, otherwise
                 * forget we've ever seen it.
                 */
                if (curr) {
                        if (curr->on_rq)
                                update_curr(cfs_rq);
                        else
                                curr = NULL;

                        /*
                         * This call to check_cfs_rq_runtime() will do the
                         * throttle and dequeue its entity in the parent(s).
                         * Therefore the nr_running test will indeed
                         * be correct.
                         */
                        if (unlikely(check_cfs_rq_runtime(cfs_rq))) {
                                cfs_rq = &rq->cfs;

                                if (!cfs_rq->nr_running)
                                        goto idle;

                                goto simple;
                        }
                }

                se = pick_next_entity(cfs_rq, curr);
                cfs_rq = group_cfs_rq(se);
        } while (cfs_rq);

        p = task_of(se);

        /*
         * Since we haven't yet done put_prev_entity and if the selected task
         * is a different task than we started out with, try and touch the
         * least amount of cfs_rqs.
         */
        if (prev != p) {
                struct sched_entity *pse = &prev->se;

                while (!(cfs_rq = is_same_group(se, pse))) {
                        int se_depth = se->depth;
                        int pse_depth = pse->depth;

                        if (se_depth <= pse_depth) {
                                put_prev_entity(cfs_rq_of(pse), pse);
                                pse = parent_entity(pse);
                        }
                        if (se_depth >= pse_depth) {
                                set_next_entity(cfs_rq_of(se), se);
                                se = parent_entity(se);
                        }
                }

                put_prev_entity(cfs_rq, pse);
                set_next_entity(cfs_rq, se);
        }

        goto done;
simple:
#endif

        put_prev_task(rq, prev);

        do {
                se = pick_next_entity(cfs_rq, NULL);
                set_next_entity(cfs_rq, se);
                cfs_rq = group_cfs_rq(se);
        } while (cfs_rq);

        p = task_of(se);

done: __maybe_unused;
#ifdef CONFIG_SMP
        /*
         * Move the next running task to the front of
         * the list, so our cfs_tasks list becomes MRU
         * one.
         */
        list_move(&p->se.group_node, &rq->cfs_tasks);
#endif

        if (hrtick_enabled(rq))
                hrtick_start_fair(rq, p);

        return p;

idle:
        new_tasks = idle_balance(rq, rf);

        /*
         * Because idle_balance() releases (and re-acquires) rq->lock, it is
         * possible for any higher priority task to appear. In that case we
         * must re-start the pick_next_entity() loop.
         */
        if (new_tasks < 0)
                return RETRY_TASK;

        if (new_tasks > 0)
                goto again;

        return NULL;
}

/*
 * Account for a descheduled task:
 */
static void put_prev_task_fair(struct rq *rq, struct task_struct *prev)
{
        struct sched_entity *se = &prev->se;
        struct cfs_rq *cfs_rq;

        for_each_sched_entity(se) {
                cfs_rq = cfs_rq_of(se);
                put_prev_entity(cfs_rq, se);
        }
}

/*
 * sched_yield() is very simple
 *
 * The magic of dealing with the ->skip buddy is in pick_next_entity.
 */
static void yield_task_fair(struct rq *rq)
{
        struct task_struct *curr = rq->curr;
        struct cfs_rq *cfs_rq = task_cfs_rq(curr);
        struct sched_entity *se = &curr->se;

        /*
         * Are we the only task in the tree?
         */
        if (unlikely(rq->nr_running == 1))
                return;

        clear_buddies(cfs_rq, se);

        if (curr->policy != SCHED_BATCH) {
                update_rq_clock(rq);
                /*
                 * Update run-time statistics of the 'current'.
                 */
                update_curr(cfs_rq);
                /*
                 * Tell update_rq_clock() that we've just updated,
                 * so we don't do microscopic update in schedule()
                 * and double the fastpath cost.
                 */
                rq_clock_skip_update(rq);
        }

        set_skip_buddy(se);
}

static bool yield_to_task_fair(struct rq *rq, struct task_struct *p, bool preempt)
{
        struct sched_entity *se = &p->se;

        /* throttled hierarchies are not runnable */
        if (!se->on_rq || throttled_hierarchy(cfs_rq_of(se)))
                return false;

        /* Tell the scheduler that we'd really like pse to run next. */
        set_next_buddy(se);

        yield_task_fair(rq);

        return true;
}

#ifdef CONFIG_SMP
/**************************************************
 * Fair scheduling class load-balancing methods.
 *
 * BASICS
 *
 * The purpose of load-balancing is to achieve the same basic fairness the
 * per-CPU scheduler provides, namely provide a proportional amount of compute
 * time to each task. This is expressed in the following equation:
 *
 *   W_i,n/P_i == W_j,n/P_j for all i,j                               (1)
 *
 * Where W_i,n is the n-th weight average for CPU i. The instantaneous weight
 * W_i,0 is defined as:
 *
 *   W_i,0 = \Sum_j w_i,j                                             (2)
 *
 * Where w_i,j is the weight of the j-th runnable task on CPU i. This weight
 * is derived from the nice value as per sched_prio_to_weight[].
 *
 * The weight average is an exponential decay average of the instantaneous
 * weight:
 *
 *   W'_i,n = (2^n - 1) / 2^n * W_i,n + 1 / 2^n * W_i,0               (3)
 *
 * C_i is the compute capacity of CPU i, typically it is the
 * fraction of 'recent' time available for SCHED_OTHER task execution. But it
 * can also include other factors [XXX].
 *
 * To achieve this balance we define a measure of imbalance which follows
 * directly from (1):
 *
 *   imb_i,j = max{ avg(W/C), W_i/C_i } - min{ avg(W/C), W_j/C_j }    (4)
 *
 * We them move tasks around to minimize the imbalance. In the continuous
 * function space it is obvious this converges, in the discrete case we get
 * a few fun cases generally called infeasible weight scenarios.
 *
 * [XXX expand on:
 *     - infeasible weights;
 *     - local vs global optima in the discrete case. ]
 *
 *
 * SCHED DOMAINS
 *
 * In order to solve the imbalance equation (4), and avoid the obvious O(n^2)
 * for all i,j solution, we create a tree of CPUs that follows the hardware
 * topology where each level pairs two lower groups (or better). This results
 * in O(log n) layers. Furthermore we reduce the number of CPUs going up the
 * tree to only the first of the previous level and we decrease the frequency
 * of load-balance at each level inv. proportional to the number of CPUs in
 * the groups.
 *
 * This yields:
 *
 *     log_2 n     1     n
 *   \Sum       { --- * --- * 2^i } = O(n)                            (5)
 *     i = 0      2^i   2^i
 *                               `- size of each group
 *         |         |     `- number of CPUs doing load-balance
 *         |         `- freq
 *         `- sum over all levels
 *
 * Coupled with a limit on how many tasks we can migrate every balance pass,
 * this makes (5) the runtime complexity of the balancer.
 *
 * An important property here is that each CPU is still (indirectly) connected
 * to every other CPU in at most O(log n) steps:
 *
 * The adjacency matrix of the resulting graph is given by:
 *
 *             log_2 n
 *   A_i,j = \Union     (i % 2^k == 0) && i / 2^(k+1) == j / 2^(k+1)  (6)
 *             k = 0
 *
 * And you'll find that:
 *
 *   A^(log_2 n)_i,j != 0  for all i,j                                (7)
 *
 * Showing there's indeed a path between every CPU in at most O(log n) steps.
 * The task movement gives a factor of O(m), giving a convergence complexity
 * of:
 *
 *   O(nm log n),  n := nr_cpus, m := nr_tasks                        (8)
 *
 *
 * WORK CONSERVING
 *
 * In order to avoid CPUs going idle while there's still work to do, new idle
 * balancing is more aggressive and has the newly idle CPU iterate up the domain
 * tree itself instead of relying on other CPUs to bring it work.
 *
 * This adds some complexity to both (5) and (8) but it reduces the total idle
 * time.
 *
 * [XXX more?]
 *
 *
 * CGROUPS
 *
 * Cgroups make a horror show out of (2), instead of a simple sum we get:
 *
 *                                s_k,i
 *   W_i,0 = \Sum_j \Prod_k w_k * -----                               (9)
 *                                 S_k
 *
 * Where
 *
 *   s_k,i = \Sum_j w_i,j,k  and  S_k = \Sum_i s_k,i                 (10)
 *
 * w_i,j,k is the weight of the j-th runnable task in the k-th cgroup on CPU i.
 *
 * The big problem is S_k, its a global sum needed to compute a local (W_i)
 * property.
 *
 * [XXX write more on how we solve this.. _after_ merging pjt's patches that
 *      rewrite all of this once again.]
 */

static unsigned long __read_mostly max_load_balance_interval = HZ/10;

enum fbq_type { regular, remote, all };

#define LBF_ALL_PINNED  0x01
#define LBF_NEED_BREAK  0x02
#define LBF_DST_PINNED  0x04
#define LBF_SOME_PINNED 0x08
#define LBF_NOHZ_STATS  0x10
#define LBF_NOHZ_AGAIN  0x20

struct lb_env {
        struct sched_domain     *sd;

        struct rq               *src_rq;
        int                     src_cpu;

        int                     dst_cpu;
        struct rq               *dst_rq;

        struct cpumask          *dst_grpmask;
        int                     new_dst_cpu;
        enum cpu_idle_type      idle;
        long                    imbalance;
        /* The set of CPUs under consideration for load-balancing */
        struct cpumask          *cpus;

        unsigned int            flags;

        unsigned int            loop;
        unsigned int            loop_break;
        unsigned int            loop_max;

        enum fbq_type           fbq_type;
        struct list_head        tasks;
};

/*
 * Is this task likely cache-hot:
 */
static int task_hot(struct task_struct *p, struct lb_env *env)
{
        s64 delta;

        lockdep_assert_held(&env->src_rq->lock);

        if (p->sched_class != &fair_sched_class)
                return 0;

        if (unlikely(p->policy == SCHED_IDLE))
                return 0;

        /*
         * Buddy candidates are cache hot:
         */
        if (sched_feat(CACHE_HOT_BUDDY) && env->dst_rq->nr_running &&
                        (&p->se == cfs_rq_of(&p->se)->next ||
                         &p->se == cfs_rq_of(&p->se)->last))
                return 1;

        if (sysctl_sched_migration_cost == -1)
                return 1;
        if (sysctl_sched_migration_cost == 0)
                return 0;

        delta = rq_clock_task(env->src_rq) - p->se.exec_start;

        return delta < (s64)sysctl_sched_migration_cost;
}

#ifdef CONFIG_NUMA_BALANCING
/*
 * Returns 1, if task migration degrades locality
 * Returns 0, if task migration improves locality i.e migration preferred.
 * Returns -1, if task migration is not affected by locality.
 */
static int migrate_degrades_locality(struct task_struct *p, struct lb_env *env)
{
        struct numa_group *numa_group = rcu_dereference(p->numa_group);
        unsigned long src_weight, dst_weight;
        int src_nid, dst_nid, dist;

        if (!static_branch_likely(&sched_numa_balancing))
                return -1;

        if (!p->numa_faults || !(env->sd->flags & SD_NUMA))
                return -1;

        src_nid = cpu_to_node(env->src_cpu);
        dst_nid = cpu_to_node(env->dst_cpu);

        if (src_nid == dst_nid)
                return -1;

        /* Migrating away from the preferred node is always bad. */
        if (src_nid == p->numa_preferred_nid) {
                if (env->src_rq->nr_running > env->src_rq->nr_preferred_running)
                        return 1;
                else
                        return -1;
        }

        /* Encourage migration to the preferred node. */
        if (dst_nid == p->numa_preferred_nid)
                return 0;

        /* Leaving a core idle is often worse than degrading locality. */
        if (env->idle == CPU_IDLE)
                return -1;

        dist = node_distance(src_nid, dst_nid);
        if (numa_group) {
                src_weight = group_weight(p, src_nid, dist);
                dst_weight = group_weight(p, dst_nid, dist);
        } else {
                src_weight = task_weight(p, src_nid, dist);
                dst_weight = task_weight(p, dst_nid, dist);
        }

        return dst_weight < src_weight;
}

#else
static inline int migrate_degrades_locality(struct task_struct *p,
                                             struct lb_env *env)
{
        return -1;
}
#endif

/*
 * can_migrate_task - may task p from runqueue rq be migrated to this_cpu?
 */
static
int can_migrate_task(struct task_struct *p, struct lb_env *env)
{
        int tsk_cache_hot;

        lockdep_assert_held(&env->src_rq->lock);

        /*
         * We do not migrate tasks that are:
         * 1) throttled_lb_pair, or
         * 2) cannot be migrated to this CPU due to cpus_allowed, or
         * 3) running (obviously), or
         * 4) are cache-hot on their current CPU.
         */
        if (throttled_lb_pair(task_group(p), env->src_cpu, env->dst_cpu))
                return 0;

        if (!cpumask_test_cpu(env->dst_cpu, &p->cpus_allowed)) {
                int cpu;

                schedstat_inc(p->se.statistics.nr_failed_migrations_affine);

                env->flags |= LBF_SOME_PINNED;

                /*
                 * Remember if this task can be migrated to any other CPU in
                 * our sched_group. We may want to revisit it if we couldn't
                 * meet load balance goals by pulling other tasks on src_cpu.
                 *
                 * Avoid computing new_dst_cpu for NEWLY_IDLE or if we have
                 * already computed one in current iteration.
                 */
                if (env->idle == CPU_NEWLY_IDLE || (env->flags & LBF_DST_PINNED))
                        return 0;

                /* Prevent to re-select dst_cpu via env's CPUs: */
                for_each_cpu_and(cpu, env->dst_grpmask, env->cpus) {
                        if (cpumask_test_cpu(cpu, &p->cpus_allowed)) {
                                env->flags |= LBF_DST_PINNED;
                                env->new_dst_cpu = cpu;
                                break;
                        }
                }

                return 0;
        }

        /* Record that we found atleast one task that could run on dst_cpu */
        env->flags &= ~LBF_ALL_PINNED;

        if (task_running(env->src_rq, p)) {
                schedstat_inc(p->se.statistics.nr_failed_migrations_running);
                return 0;
        }

        /*
         * Aggressive migration if:
         * 1) destination numa is preferred
         * 2) task is cache cold, or
         * 3) too many balance attempts have failed.
         */
        tsk_cache_hot = migrate_degrades_locality(p, env);
        if (tsk_cache_hot == -1)
                tsk_cache_hot = task_hot(p, env);

        if (tsk_cache_hot <= 0 ||
            env->sd->nr_balance_failed > env->sd->cache_nice_tries) {
                if (tsk_cache_hot == 1) {
                        schedstat_inc(env->sd->lb_hot_gained[env->idle]);
                        schedstat_inc(p->se.statistics.nr_forced_migrations);
                }
                return 1;
        }

        schedstat_inc(p->se.statistics.nr_failed_migrations_hot);
        return 0;
}

/*
 * detach_task() -- detach the task for the migration specified in env
 */
static void detach_task(struct task_struct *p, struct lb_env *env)
{
        lockdep_assert_held(&env->src_rq->lock);

        p->on_rq = TASK_ON_RQ_MIGRATING;
        deactivate_task(env->src_rq, p, DEQUEUE_NOCLOCK);
        set_task_cpu(p, env->dst_cpu);
}

/*
 * detach_one_task() -- tries to dequeue exactly one task from env->src_rq, as
 * part of active balancing operations within "domain".
 *
 * Returns a task if successful and NULL otherwise.
 */
static struct task_struct *detach_one_task(struct lb_env *env)
{
        struct task_struct *p;

        lockdep_assert_held(&env->src_rq->lock);

        list_for_each_entry_reverse(p,
                        &env->src_rq->cfs_tasks, se.group_node) {
                if (!can_migrate_task(p, env))
                        continue;

                detach_task(p, env);

                /*
                 * Right now, this is only the second place where
                 * lb_gained[env->idle] is updated (other is detach_tasks)
                 * so we can safely collect stats here rather than
                 * inside detach_tasks().
                 */
                schedstat_inc(env->sd->lb_gained[env->idle]);
                return p;
        }
        return NULL;
}

static const unsigned int sched_nr_migrate_break = 32;

/*
 * detach_tasks() -- tries to detach up to imbalance weighted load from
 * busiest_rq, as part of a balancing operation within domain "sd".
 *
 * Returns number of detached tasks if successful and 0 otherwise.
 */
static int detach_tasks(struct lb_env *env)
{
        struct list_head *tasks = &env->src_rq->cfs_tasks;
        struct task_struct *p;
        unsigned long load;
        int detached = 0;

        lockdep_assert_held(&env->src_rq->lock);

        if (env->imbalance <= 0)
                return 0;

        while (!list_empty(tasks)) {
                /*
                 * We don't want to steal all, otherwise we may be treated likewise,
                 * which could at worst lead to a livelock crash.
                 */
                if (env->idle != CPU_NOT_IDLE && env->src_rq->nr_running <= 1)
                        break;

                p = list_last_entry(tasks, struct task_struct, se.group_node);

                env->loop++;
                /* We've more or less seen every task there is, call it quits */
                if (env->loop > env->loop_max)
                        break;

                /* take a breather every nr_migrate tasks */
                if (env->loop > env->loop_break) {
                        env->loop_break += sched_nr_migrate_break;
                        env->flags |= LBF_NEED_BREAK;
                        break;
                }

                if (!can_migrate_task(p, env))
                        goto next;

                load = task_h_load(p);

                if (sched_feat(LB_MIN) && load < 16 && !env->sd->nr_balance_failed)
                        goto next;

                if ((load / 2) > env->imbalance)
                        goto next;

                detach_task(p, env);
                list_add(&p->se.group_node, &env->tasks);

                detached++;
                env->imbalance -= load;

#ifdef CONFIG_PREEMPT
                /*
                 * NEWIDLE balancing is a source of latency, so preemptible
                 * kernels will stop after the first task is detached to minimize
                 * the critical section.
                 */
                if (env->idle == CPU_NEWLY_IDLE)
                        break;
#endif

                /*
                 * We only want to steal up to the prescribed amount of
                 * weighted load.
                 */
                if (env->imbalance <= 0)
                        break;

                continue;
next:
                list_move(&p->se.group_node, tasks);
        }

        /*
         * Right now, this is one of only two places we collect this stat
         * so we can safely collect detach_one_task() stats here rather
         * than inside detach_one_task().
         */
        schedstat_add(env->sd->lb_gained[env->idle], detached);

        return detached;
}

/*
 * attach_task() -- attach the task detached by detach_task() to its new rq.
 */
static void attach_task(struct rq *rq, struct task_struct *p)
{
        lockdep_assert_held(&rq->lock);

        BUG_ON(task_rq(p) != rq);
        activate_task(rq, p, ENQUEUE_NOCLOCK);
        p->on_rq = TASK_ON_RQ_QUEUED;
        check_preempt_curr(rq, p, 0);
}

/*
 * attach_one_task() -- attaches the task returned from detach_one_task() to
 * its new rq.
 */
static void attach_one_task(struct rq *rq, struct task_struct *p)
{
        struct rq_flags rf;

        rq_lock(rq, &rf);
        update_rq_clock(rq);
        attach_task(rq, p);
        rq_unlock(rq, &rf);
}

/*
 * attach_tasks() -- attaches all tasks detached by detach_tasks() to their
 * new rq.
 */
static void attach_tasks(struct lb_env *env)
{
        struct list_head *tasks = &env->tasks;
        struct task_struct *p;
        struct rq_flags rf;

        rq_lock(env->dst_rq, &rf);
        update_rq_clock(env->dst_rq);

        while (!list_empty(tasks)) {
                p = list_first_entry(tasks, struct task_struct, se.group_node);
                list_del_init(&p->se.group_node);

                attach_task(env->dst_rq, p);
        }

        rq_unlock(env->dst_rq, &rf);
}

static inline bool cfs_rq_has_blocked(struct cfs_rq *cfs_rq)
{
        if (cfs_rq->avg.load_avg)
                return true;

        if (cfs_rq->avg.util_avg)
                return true;

        return false;
}

static inline bool others_have_blocked(struct rq *rq)
{
        if (READ_ONCE(rq->avg_rt.util_avg))
                return true;

        if (READ_ONCE(rq->avg_dl.util_avg))
                return true;

#if defined(CONFIG_IRQ_TIME_ACCOUNTING) || defined(CONFIG_PARAVIRT_TIME_ACCOUNTING)
        if (READ_ONCE(rq->avg_irq.util_avg))
                return true;
#endif

        return false;
}

#ifdef CONFIG_FAIR_GROUP_SCHED

static inline bool cfs_rq_is_decayed(struct cfs_rq *cfs_rq)
{
        if (cfs_rq->load.weight)
                return false;

        if (cfs_rq->avg.load_sum)
                return false;

        if (cfs_rq->avg.util_sum)
                return false;

        if (cfs_rq->avg.runnable_load_sum)
                return false;

        return true;
}

static void update_blocked_averages(int cpu)
{
        struct rq *rq = cpu_rq(cpu);
        struct cfs_rq *cfs_rq, *pos;
        const struct sched_class *curr_class;
        struct rq_flags rf;
        bool done = true;

        rq_lock_irqsave(rq, &rf);
        update_rq_clock(rq);

        /*
         * Iterates the task_group tree in a bottom up fashion, see
         * list_add_leaf_cfs_rq() for details.
         */
        for_each_leaf_cfs_rq_safe(rq, cfs_rq, pos) {
                struct sched_entity *se;

                /* throttled entities do not contribute to load */
                if (throttled_hierarchy(cfs_rq))
                        continue;

                if (update_cfs_rq_load_avg(cfs_rq_clock_task(cfs_rq), cfs_rq))
                        update_tg_load_avg(cfs_rq, 0);

                /* Propagate pending load changes to the parent, if any: */
                se = cfs_rq->tg->se[cpu];
                if (se && !skip_blocked_update(se))
                        update_load_avg(cfs_rq_of(se), se, 0);

                /*
                 * There can be a lot of idle CPU cgroups.  Don't let fully
                 * decayed cfs_rqs linger on the list.
                 */
                if (cfs_rq_is_decayed(cfs_rq))
                        list_del_leaf_cfs_rq(cfs_rq);

                /* Don't need periodic decay once load/util_avg are null */
                if (cfs_rq_has_blocked(cfs_rq))
                        done = false;
        }

        curr_class = rq->curr->sched_class;
        update_rt_rq_load_avg(rq_clock_task(rq), rq, curr_class == &rt_sched_class);
        update_dl_rq_load_avg(rq_clock_task(rq), rq, curr_class == &dl_sched_class);
        update_irq_load_avg(rq, 0);
        /* Don't need periodic decay once load/util_avg are null */
        if (others_have_blocked(rq))
                done = false;

#ifdef CONFIG_NO_HZ_COMMON
        rq->last_blocked_load_update_tick = jiffies;
        if (done)
                rq->has_blocked_load = 0;
#endif
        rq_unlock_irqrestore(rq, &rf);
}

/*
 * Compute the hierarchical load factor for cfs_rq and all its ascendants.
 * This needs to be done in a top-down fashion because the load of a child
 * group is a fraction of its parents load.
 */
static void update_cfs_rq_h_load(struct cfs_rq *cfs_rq)
{
        struct rq *rq = rq_of(cfs_rq);
        struct sched_entity *se = cfs_rq->tg->se[cpu_of(rq)];
        unsigned long now = jiffies;
        unsigned long load;

        if (cfs_rq->last_h_load_update == now)
                return;

        cfs_rq->h_load_next = NULL;
        for_each_sched_entity(se) {
                cfs_rq = cfs_rq_of(se);
                cfs_rq->h_load_next = se;
                if (cfs_rq->last_h_load_update == now)
                        break;
        }

        if (!se) {
                cfs_rq->h_load = cfs_rq_load_avg(cfs_rq);
                cfs_rq->last_h_load_update = now;
        }

        while ((se = cfs_rq->h_load_next) != NULL) {
                load = cfs_rq->h_load;
                load = div64_ul(load * se->avg.load_avg,
                        cfs_rq_load_avg(cfs_rq) + 1);
                cfs_rq = group_cfs_rq(se);
                cfs_rq->h_load = load;
                cfs_rq->last_h_load_update = now;
        }
}

static unsigned long task_h_load(struct task_struct *p)
{
        struct cfs_rq *cfs_rq = task_cfs_rq(p);

        update_cfs_rq_h_load(cfs_rq);
        return div64_ul(p->se.avg.load_avg * cfs_rq->h_load,
                        cfs_rq_load_avg(cfs_rq) + 1);
}
#else
static inline void update_blocked_averages(int cpu)
{
        struct rq *rq = cpu_rq(cpu);
        struct cfs_rq *cfs_rq = &rq->cfs;
        const struct sched_class *curr_class;
        struct rq_flags rf;

        rq_lock_irqsave(rq, &rf);
        update_rq_clock(rq);
        update_cfs_rq_load_avg(cfs_rq_clock_task(cfs_rq), cfs_rq);

        curr_class = rq->curr->sched_class;
        update_rt_rq_load_avg(rq_clock_task(rq), rq, curr_class == &rt_sched_class);
        update_dl_rq_load_avg(rq_clock_task(rq), rq, curr_class == &dl_sched_class);
        update_irq_load_avg(rq, 0);
#ifdef CONFIG_NO_HZ_COMMON
        rq->last_blocked_load_update_tick = jiffies;
        if (!cfs_rq_has_blocked(cfs_rq) && !others_have_blocked(rq))
                rq->has_blocked_load = 0;
#endif
        rq_unlock_irqrestore(rq, &rf);
}

static unsigned long task_h_load(struct task_struct *p)
{
        return p->se.avg.load_avg;
}
#endif

/********** Helpers for find_busiest_group ************************/

enum group_type {
        group_other = 0,
        group_imbalanced,
        group_overloaded,
};

/*
 * sg_lb_stats - stats of a sched_group required for load_balancing
 */
struct sg_lb_stats {
        unsigned long avg_load; /*Avg load across the CPUs of the group */
        unsigned long group_load; /* Total load over the CPUs of the group */
        unsigned long sum_weighted_load; /* Weighted load of group's tasks */
        unsigned long load_per_task;
        unsigned long group_capacity;
        unsigned long group_util; /* Total utilization of the group */
        unsigned int sum_nr_running; /* Nr tasks running in the group */
        unsigned int idle_cpus;
        unsigned int group_weight;
        enum group_type group_type;
        int group_no_capacity;
#ifdef CONFIG_NUMA_BALANCING
        unsigned int nr_numa_running;
        unsigned int nr_preferred_running;
#endif
};

/*
 * sd_lb_stats - Structure to store the statistics of a sched_domain
 *               during load balancing.
 */
struct sd_lb_stats {
        struct sched_group *busiest;    /* Busiest group in this sd */
        struct sched_group *local;      /* Local group in this sd */
        unsigned long total_running;
        unsigned long total_load;       /* Total load of all groups in sd */
        unsigned long total_capacity;   /* Total capacity of all groups in sd */
        unsigned long avg_load; /* Average load across all groups in sd */

        struct sg_lb_stats busiest_stat;/* Statistics of the busiest group */
        struct sg_lb_stats local_stat;  /* Statistics of the local group */
};

static inline void init_sd_lb_stats(struct sd_lb_stats *sds)
{
        /*
         * Skimp on the clearing to avoid duplicate work. We can avoid clearing
         * local_stat because update_sg_lb_stats() does a full clear/assignment.
         * We must however clear busiest_stat::avg_load because
         * update_sd_pick_busiest() reads this before assignment.
         */
        *sds = (struct sd_lb_stats){
                .busiest = NULL,
                .local = NULL,
                .total_running = 0UL,
                .total_load = 0UL,
                .total_capacity = 0UL,
                .busiest_stat = {
                        .avg_load = 0UL,
                        .sum_nr_running = 0,
                        .group_type = group_other,
                },
        };
}

/**
 * get_sd_load_idx - Obtain the load index for a given sched domain.
 * @sd: The sched_domain whose load_idx is to be obtained.
 * @idle: The idle status of the CPU for whose sd load_idx is obtained.
 *
 * Return: The load index.
 */
static inline int get_sd_load_idx(struct sched_domain *sd,
                                        enum cpu_idle_type idle)
{
        int load_idx;

        switch (idle) {
        case CPU_NOT_IDLE:
                load_idx = sd->busy_idx;
                break;

        case CPU_NEWLY_IDLE:
                load_idx = sd->newidle_idx;
                break;
        default:
                load_idx = sd->idle_idx;
                break;
        }

        return load_idx;
}

static unsigned long scale_rt_capacity(struct sched_domain *sd, int cpu)
{
        struct rq *rq = cpu_rq(cpu);
        unsigned long max = arch_scale_cpu_capacity(sd, cpu);
        unsigned long used, free;
        unsigned long irq;

        irq = cpu_util_irq(rq);

        if (unlikely(irq >= max))
                return 1;

        used = READ_ONCE(rq->avg_rt.util_avg);
        used += READ_ONCE(rq->avg_dl.util_avg);

        if (unlikely(used >= max))
                return 1;

        free = max - used;

        return scale_irq_capacity(free, irq, max);
}

static void update_cpu_capacity(struct sched_domain *sd, int cpu)
{
        unsigned long capacity = scale_rt_capacity(sd, cpu);
        struct sched_group *sdg = sd->groups;

        cpu_rq(cpu)->cpu_capacity_orig = arch_scale_cpu_capacity(sd, cpu);

        if (!capacity)
                capacity = 1;

        cpu_rq(cpu)->cpu_capacity = capacity;
        sdg->sgc->capacity = capacity;
        sdg->sgc->min_capacity = capacity;
}

void update_group_capacity(struct sched_domain *sd, int cpu)
{
        struct sched_domain *child = sd->child;
        struct sched_group *group, *sdg = sd->groups;
        unsigned long capacity, min_capacity;
        unsigned long interval;

        interval = msecs_to_jiffies(sd->balance_interval);
        interval = clamp(interval, 1UL, max_load_balance_interval);
        sdg->sgc->next_update = jiffies + interval;

        if (!child) {
                update_cpu_capacity(sd, cpu);
                return;
        }

        capacity = 0;
        min_capacity = ULONG_MAX;

        if (child->flags & SD_OVERLAP) {
                /*
                 * SD_OVERLAP domains cannot assume that child groups
                 * span the current group.
                 */

                for_each_cpu(cpu, sched_group_span(sdg)) {
                        struct sched_group_capacity *sgc;
                        struct rq *rq = cpu_rq(cpu);

                        /*
                         * build_sched_domains() -> init_sched_groups_capacity()
                         * gets here before we've attached the domains to the
                         * runqueues.
                         *
                         * Use capacity_of(), which is set irrespective of domains
                         * in update_cpu_capacity().
                         *
                         * This avoids capacity from being 0 and
                         * causing divide-by-zero issues on boot.
                         */
                        if (unlikely(!rq->sd)) {
                                capacity += capacity_of(cpu);
                        } else {
                                sgc = rq->sd->groups->sgc;
                                capacity += sgc->capacity;
                        }

                        min_capacity = min(capacity, min_capacity);
                }
        } else  {
                /*
                 * !SD_OVERLAP domains can assume that child groups
                 * span the current group.
                 */

                group = child->groups;
                do {
                        struct sched_group_capacity *sgc = group->sgc;

                        capacity += sgc->capacity;
                        min_capacity = min(sgc->min_capacity, min_capacity);
                        group = group->next;
                } while (group != child->groups);
        }

        sdg->sgc->capacity = capacity;
        sdg->sgc->min_capacity = min_capacity;
}

/*
 * Check whether the capacity of the rq has been noticeably reduced by side
 * activity. The imbalance_pct is used for the threshold.
 * Return true is the capacity is reduced
 */
static inline int
check_cpu_capacity(struct rq *rq, struct sched_domain *sd)
{
        return ((rq->cpu_capacity * sd->imbalance_pct) <
                                (rq->cpu_capacity_orig * 100));
}

/*
 * Group imbalance indicates (and tries to solve) the problem where balancing
 * groups is inadequate due to ->cpus_allowed constraints.
 *
 * Imagine a situation of two groups of 4 CPUs each and 4 tasks each with a
 * cpumask covering 1 CPU of the first group and 3 CPUs of the second group.
 * Something like:
 *
 *      { 0 1 2 3 } { 4 5 6 7 }
 *              *     * * *
 *
 * If we were to balance group-wise we'd place two tasks in the first group and
 * two tasks in the second group. Clearly this is undesired as it will overload
 * cpu 3 and leave one of the CPUs in the second group unused.
 *
 * The current solution to this issue is detecting the skew in the first group
 * by noticing the lower domain failed to reach balance and had difficulty
 * moving tasks due to affinity constraints.
 *
 * When this is so detected; this group becomes a candidate for busiest; see
 * update_sd_pick_busiest(). And calculate_imbalance() and
 * find_busiest_group() avoid some of the usual balance conditions to allow it
 * to create an effective group imbalance.
 *
 * This is a somewhat tricky proposition since the next run might not find the
 * group imbalance and decide the groups need to be balanced again. A most
 * subtle and fragile situation.
 */

static inline int sg_imbalanced(struct sched_group *group)
{
        return group->sgc->imbalance;
}

/*
 * group_has_capacity returns true if the group has spare capacity that could
 * be used by some tasks.
 * We consider that a group has spare capacity if the  * number of task is
 * smaller than the number of CPUs or if the utilization is lower than the
 * available capacity for CFS tasks.
 * For the latter, we use a threshold to stabilize the state, to take into
 * account the variance of the tasks' load and to return true if the available
 * capacity in meaningful for the load balancer.
 * As an example, an available capacity of 1% can appear but it doesn't make
 * any benefit for the load balance.
 */
static inline bool
group_has_capacity(struct lb_env *env, struct sg_lb_stats *sgs)
{
        if (sgs->sum_nr_running < sgs->group_weight)
                return true;

        if ((sgs->group_capacity * 100) >
                        (sgs->group_util * env->sd->imbalance_pct))
                return true;

        return false;
}

/*
 *  group_is_overloaded returns true if the group has more tasks than it can
 *  handle.
 *  group_is_overloaded is not equals to !group_has_capacity because a group
 *  with the exact right number of tasks, has no more spare capacity but is not
 *  overloaded so both group_has_capacity and group_is_overloaded return
 *  false.
 */
static inline bool
group_is_overloaded(struct lb_env *env, struct sg_lb_stats *sgs)
{
        if (sgs->sum_nr_running <= sgs->group_weight)
                return false;

        if ((sgs->group_capacity * 100) <
                        (sgs->group_util * env->sd->imbalance_pct))
                return true;

        return false;
}

/*
 * group_smaller_cpu_capacity: Returns true if sched_group sg has smaller
 * per-CPU capacity than sched_group ref.
 */
static inline bool
group_smaller_cpu_capacity(struct sched_group *sg, struct sched_group *ref)
{
        return sg->sgc->min_capacity * capacity_margin <
                                                ref->sgc->min_capacity * 1024;
}

static inline enum
group_type group_classify(struct sched_group *group,
                          struct sg_lb_stats *sgs)
{
        if (sgs->group_no_capacity)
                return group_overloaded;

        if (sg_imbalanced(group))
                return group_imbalanced;

        return group_other;
}

static bool update_nohz_stats(struct rq *rq, bool force)
{
#ifdef CONFIG_NO_HZ_COMMON
        unsigned int cpu = rq->cpu;

        if (!rq->has_blocked_load)
                return false;

        if (!cpumask_test_cpu(cpu, nohz.idle_cpus_mask))
                return false;

        if (!force && !time_after(jiffies, rq->last_blocked_load_update_tick))
                return true;

        update_blocked_averages(cpu);

        return rq->has_blocked_load;
#else
        return false;
#endif
}

/**
 * update_sg_lb_stats - Update sched_group's statistics for load balancing.
 * @env: The load balancing environment.
 * @group: sched_group whose statistics are to be updated.
 * @load_idx: Load index of sched_domain of this_cpu for load calc.
 * @local_group: Does group contain this_cpu.
 * @sgs: variable to hold the statistics for this group.
 * @overload: Indicate more than one runnable task for any CPU.
 */
static inline void update_sg_lb_stats(struct lb_env *env,
                        struct sched_group *group, int load_idx,
                        int local_group, struct sg_lb_stats *sgs,
                        bool *overload)
{
        unsigned long load;
        int i, nr_running;

        memset(sgs, 0, sizeof(*sgs));

        for_each_cpu_and(i, sched_group_span(group), env->cpus) {
                struct rq *rq = cpu_rq(i);

                if ((env->flags & LBF_NOHZ_STATS) && update_nohz_stats(rq, false))
                        env->flags |= LBF_NOHZ_AGAIN;

                /* Bias balancing toward CPUs of our domain: */
                if (local_group)
                        load = target_load(i, load_idx);
                else
                        load = source_load(i, load_idx);

                sgs->group_load += load;
                sgs->group_util += cpu_util(i);
                sgs->sum_nr_running += rq->cfs.h_nr_running;

                nr_running = rq->nr_running;
                if (nr_running > 1)
                        *overload = true;

#ifdef CONFIG_NUMA_BALANCING
                sgs->nr_numa_running += rq->nr_numa_running;
                sgs->nr_preferred_running += rq->nr_preferred_running;
#endif
                sgs->sum_weighted_load += weighted_cpuload(rq);
                /*
                 * No need to call idle_cpu() if nr_running is not 0
                 */
                if (!nr_running && idle_cpu(i))
                        sgs->idle_cpus++;
        }

        /* Adjust by relative CPU capacity of the group */
        sgs->group_capacity = group->sgc->capacity;
        sgs->avg_load = (sgs->group_load*SCHED_CAPACITY_SCALE) / sgs->group_capacity;

        if (sgs->sum_nr_running)
                sgs->load_per_task = sgs->sum_weighted_load / sgs->sum_nr_running;

        sgs->group_weight = group->group_weight;

        sgs->group_no_capacity = group_is_overloaded(env, sgs);
        sgs->group_type = group_classify(group, sgs);
}

/**
 * update_sd_pick_busiest - return 1 on busiest group
 * @env: The load balancing environment.
 * @sds: sched_domain statistics
 * @sg: sched_group candidate to be checked for being the busiest
 * @sgs: sched_group statistics
 *
 * Determine if @sg is a busier group than the previously selected
 * busiest group.
 *
 * Return: %true if @sg is a busier group than the previously selected
 * busiest group. %false otherwise.
 */
static bool update_sd_pick_busiest(struct lb_env *env,
                                   struct sd_lb_stats *sds,
                                   struct sched_group *sg,
                                   struct sg_lb_stats *sgs)
{
        struct sg_lb_stats *busiest = &sds->busiest_stat;

        if (sgs->group_type > busiest->group_type)
                return true;

        if (sgs->group_type < busiest->group_type)
                return false;

        if (sgs->avg_load <= busiest->avg_load)
                return false;

        if (!(env->sd->flags & SD_ASYM_CPUCAPACITY))
                goto asym_packing;

        /*
         * Candidate sg has no more than one task per CPU and
         * has higher per-CPU capacity. Migrating tasks to less
         * capable CPUs may harm throughput. Maximize throughput,
         * power/energy consequences are not considered.
         */
        if (sgs->sum_nr_running <= sgs->group_weight &&
            group_smaller_cpu_capacity(sds->local, sg))
                return false;

asym_packing:
        /* This is the busiest node in its class. */
        if (!(env->sd->flags & SD_ASYM_PACKING))
                return true;

        /* No ASYM_PACKING if target CPU is already busy */
        if (env->idle == CPU_NOT_IDLE)
                return true;
        /*
         * ASYM_PACKING needs to move all the work to the highest
         * prority CPUs in the group, therefore mark all groups
         * of lower priority than ourself as busy.
         */
        if (sgs->sum_nr_running &&
            sched_asym_prefer(env->dst_cpu, sg->asym_prefer_cpu)) {
                if (!sds->busiest)
                        return true;

                /* Prefer to move from lowest priority CPU's work */
                if (sched_asym_prefer(sds->busiest->asym_prefer_cpu,
                                      sg->asym_prefer_cpu))
                        return true;
        }

        return false;
}

#ifdef CONFIG_NUMA_BALANCING
static inline enum fbq_type fbq_classify_group(struct sg_lb_stats *sgs)
{
        if (sgs->sum_nr_running > sgs->nr_numa_running)
                return regular;
        if (sgs->sum_nr_running > sgs->nr_preferred_running)
                return remote;
        return all;
}

static inline enum fbq_type fbq_classify_rq(struct rq *rq)
{
        if (rq->nr_running > rq->nr_numa_running)
                return regular;
        if (rq->nr_running > rq->nr_preferred_running)
                return remote;
        return all;
}
#else
static inline enum fbq_type fbq_classify_group(struct sg_lb_stats *sgs)
{
        return all;
}

static inline enum fbq_type fbq_classify_rq(struct rq *rq)
{
        return regular;
}
#endif /* CONFIG_NUMA_BALANCING */

/**
 * update_sd_lb_stats - Update sched_domain's statistics for load balancing.
 * @env: The load balancing environment.
 * @sds: variable to hold the statistics for this sched_domain.
 */
static inline void update_sd_lb_stats(struct lb_env *env, struct sd_lb_stats *sds)
{
        struct sched_domain *child = env->sd->child;
        struct sched_group *sg = env->sd->groups;
        struct sg_lb_stats *local = &sds->local_stat;
        struct sg_lb_stats tmp_sgs;
        int load_idx, prefer_sibling = 0;
        bool overload = false;

        if (child && child->flags & SD_PREFER_SIBLING)
                prefer_sibling = 1;

#ifdef CONFIG_NO_HZ_COMMON
        if (env->idle == CPU_NEWLY_IDLE && READ_ONCE(nohz.has_blocked))
                env->flags |= LBF_NOHZ_STATS;
#endif

        load_idx = get_sd_load_idx(env->sd, env->idle);

        do {
                struct sg_lb_stats *sgs = &tmp_sgs;
                int local_group;

                local_group = cpumask_test_cpu(env->dst_cpu, sched_group_span(sg));
                if (local_group) {
                        sds->local = sg;
                        sgs = local;

                        if (env->idle != CPU_NEWLY_IDLE ||
                            time_after_eq(jiffies, sg->sgc->next_update))
                                update_group_capacity(env->sd, env->dst_cpu);
                }

                update_sg_lb_stats(env, sg, load_idx, local_group, sgs,
                                                &overload);

                if (local_group)
                        goto next_group;

                /*
                 * In case the child domain prefers tasks go to siblings
                 * first, lower the sg capacity so that we'll try
                 * and move all the excess tasks away. We lower the capacity
                 * of a group only if the local group has the capacity to fit
                 * these excess tasks. The extra check prevents the case where
                 * you always pull from the heaviest group when it is already
                 * under-utilized (possible with a large weight task outweighs
                 * the tasks on the system).
                 */
                if (prefer_sibling && sds->local &&
                    group_has_capacity(env, local) &&
                    (sgs->sum_nr_running > local->sum_nr_running + 1)) {
                        sgs->group_no_capacity = 1;
                        sgs->group_type = group_classify(sg, sgs);
                }

                if (update_sd_pick_busiest(env, sds, sg, sgs)) {
                        sds->busiest = sg;
                        sds->busiest_stat = *sgs;
                }

next_group:
                /* Now, start updating sd_lb_stats */
                sds->total_running += sgs->sum_nr_running;
                sds->total_load += sgs->group_load;
                sds->total_capacity += sgs->group_capacity;

                sg = sg->next;
        } while (sg != env->sd->groups);

#ifdef CONFIG_NO_HZ_COMMON
        if ((env->flags & LBF_NOHZ_AGAIN) &&
            cpumask_subset(nohz.idle_cpus_mask, sched_domain_span(env->sd))) {

                WRITE_ONCE(nohz.next_blocked,
                           jiffies + msecs_to_jiffies(LOAD_AVG_PERIOD));
        }
#endif

        if (env->sd->flags & SD_NUMA)
                env->fbq_type = fbq_classify_group(&sds->busiest_stat);

        if (!env->sd->parent) {
                /* update overload indicator if we are at root domain */
                if (env->dst_rq->rd->overload != overload)
                        env->dst_rq->rd->overload = overload;
        }
}

/**
 * check_asym_packing - Check to see if the group is packed into the
 *                      sched domain.
 *
 * This is primarily intended to used at the sibling level.  Some
 * cores like POWER7 prefer to use lower numbered SMT threads.  In the
 * case of POWER7, it can move to lower SMT modes only when higher
 * threads are idle.  When in lower SMT modes, the threads will
 * perform better since they share less core resources.  Hence when we
 * have idle threads, we want them to be the higher ones.
 *
 * This packing function is run on idle threads.  It checks to see if
 * the busiest CPU in this domain (core in the P7 case) has a higher
 * CPU number than the packing function is being run on.  Here we are
 * assuming lower CPU number will be equivalent to lower a SMT thread
 * number.
 *
 * Return: 1 when packing is required and a task should be moved to
 * this CPU.  The amount of the imbalance is returned in env->imbalance.
 *
 * @env: The load balancing environment.
 * @sds: Statistics of the sched_domain which is to be packed
 */
static int check_asym_packing(struct lb_env *env, struct sd_lb_stats *sds)
{
        int busiest_cpu;

        if (!(env->sd->flags & SD_ASYM_PACKING))
                return 0;

        if (env->idle == CPU_NOT_IDLE)
                return 0;

        if (!sds->busiest)
                return 0;

        busiest_cpu = sds->busiest->asym_prefer_cpu;
        if (sched_asym_prefer(busiest_cpu, env->dst_cpu))
                return 0;

        env->imbalance = DIV_ROUND_CLOSEST(
                sds->busiest_stat.avg_load * sds->busiest_stat.group_capacity,
                SCHED_CAPACITY_SCALE);

        return 1;
}

/**
 * fix_small_imbalance - Calculate the minor imbalance that exists
 *                      amongst the groups of a sched_domain, during
 *                      load balancing.
 * @env: The load balancing environment.
 * @sds: Statistics of the sched_domain whose imbalance is to be calculated.
 */
static inline
void fix_small_imbalance(struct lb_env *env, struct sd_lb_stats *sds)
{
        unsigned long tmp, capa_now = 0, capa_move = 0;
        unsigned int imbn = 2;
        unsigned long scaled_busy_load_per_task;
        struct sg_lb_stats *local, *busiest;

        local = &sds->local_stat;
        busiest = &sds->busiest_stat;

        if (!local->sum_nr_running)
                local->load_per_task = cpu_avg_load_per_task(env->dst_cpu);
        else if (busiest->load_per_task > local->load_per_task)
                imbn = 1;

        scaled_busy_load_per_task =
                (busiest->load_per_task * SCHED_CAPACITY_SCALE) /
                busiest->group_capacity;

        if (busiest->avg_load + scaled_busy_load_per_task >=
            local->avg_load + (scaled_busy_load_per_task * imbn)) {
                env->imbalance = busiest->load_per_task;
                return;
        }

        /*
         * OK, we don't have enough imbalance to justify moving tasks,
         * however we may be able to increase total CPU capacity used by
         * moving them.
         */

        capa_now += busiest->group_capacity *
                        min(busiest->load_per_task, busiest->avg_load);
        capa_now += local->group_capacity *
                        min(local->load_per_task, local->avg_load);
        capa_now /= SCHED_CAPACITY_SCALE;

        /* Amount of load we'd subtract */
        if (busiest->avg_load > scaled_busy_load_per_task) {
                capa_move += busiest->group_capacity *
                            min(busiest->load_per_task,
                                busiest->avg_load - scaled_busy_load_per_task);
        }

        /* Amount of load we'd add */
        if (busiest->avg_load * busiest->group_capacity <
            busiest->load_per_task * SCHED_CAPACITY_SCALE) {
                tmp = (busiest->avg_load * busiest->group_capacity) /
                      local->group_capacity;
        } else {
                tmp = (busiest->load_per_task * SCHED_CAPACITY_SCALE) /
                      local->group_capacity;
        }
        capa_move += local->group_capacity *
                    min(local->load_per_task, local->avg_load + tmp);
        capa_move /= SCHED_CAPACITY_SCALE;

        /* Move if we gain throughput */
        if (capa_move > capa_now)
                env->imbalance = busiest->load_per_task;
}

/**
 * calculate_imbalance - Calculate the amount of imbalance present within the
 *                       groups of a given sched_domain during load balance.
 * @env: load balance environment
 * @sds: statistics of the sched_domain whose imbalance is to be calculated.
 */
static inline void calculate_imbalance(struct lb_env *env, struct sd_lb_stats *sds)
{
        unsigned long max_pull, load_above_capacity = ~0UL;
        struct sg_lb_stats *local, *busiest;

        local = &sds->local_stat;
        busiest = &sds->busiest_stat;

        if (busiest->group_type == group_imbalanced) {
                /*
                 * In the group_imb case we cannot rely on group-wide averages
                 * to ensure CPU-load equilibrium, look at wider averages. XXX
                 */
                busiest->load_per_task =
                        min(busiest->load_per_task, sds->avg_load);
        }

        /*
         * Avg load of busiest sg can be less and avg load of local sg can
         * be greater than avg load across all sgs of sd because avg load
         * factors in sg capacity and sgs with smaller group_type are
         * skipped when updating the busiest sg:
         */
        if (busiest->avg_load <= sds->avg_load ||
            local->avg_load >= sds->avg_load) {
                env->imbalance = 0;
                return fix_small_imbalance(env, sds);
        }

        /*
         * If there aren't any idle CPUs, avoid creating some.
         */
        if (busiest->group_type == group_overloaded &&
            local->group_type   == group_overloaded) {
                load_above_capacity = busiest->sum_nr_running * SCHED_CAPACITY_SCALE;
                if (load_above_capacity > busiest->group_capacity) {
                        load_above_capacity -= busiest->group_capacity;
                        load_above_capacity *= scale_load_down(NICE_0_LOAD);
                        load_above_capacity /= busiest->group_capacity;
                } else
                        load_above_capacity = ~0UL;
        }

        /*
         * We're trying to get all the CPUs to the average_load, so we don't
         * want to push ourselves above the average load, nor do we wish to
         * reduce the max loaded CPU below the average load. At the same time,
         * we also don't want to reduce the group load below the group
         * capacity. Thus we look for the minimum possible imbalance.
         */
        max_pull = min(busiest->avg_load - sds->avg_load, load_above_capacity);

        /* How much load to actually move to equalise the imbalance */
        env->imbalance = min(
                max_pull * busiest->group_capacity,
                (sds->avg_load - local->avg_load) * local->group_capacity
        ) / SCHED_CAPACITY_SCALE;

        /*
         * if *imbalance is less than the average load per runnable task
         * there is no guarantee that any tasks will be moved so we'll have
         * a think about bumping its value to force at least one task to be
         * moved
         */
        if (env->imbalance < busiest->load_per_task)
                return fix_small_imbalance(env, sds);
}

/******* find_busiest_group() helpers end here *********************/

/**
 * find_busiest_group - Returns the busiest group within the sched_domain
 * if there is an imbalance.
 *
 * Also calculates the amount of weighted load which should be moved
 * to restore balance.
 *
 * @env: The load balancing environment.
 *
 * Return:      - The busiest group if imbalance exists.
 */
static struct sched_group *find_busiest_group(struct lb_env *env)
{
        struct sg_lb_stats *local, *busiest;
        struct sd_lb_stats sds;

        init_sd_lb_stats(&sds);

        /*
         * Compute the various statistics relavent for load balancing at
         * this level.
         */
        update_sd_lb_stats(env, &sds);
        local = &sds.local_stat;
        busiest = &sds.busiest_stat;

        /* ASYM feature bypasses nice load balance check */
        if (check_asym_packing(env, &sds))
                return sds.busiest;

        /* There is no busy sibling group to pull tasks from */
        if (!sds.busiest || busiest->sum_nr_running == 0)
                goto out_balanced;

        /* XXX broken for overlapping NUMA groups */
        sds.avg_load = (SCHED_CAPACITY_SCALE * sds.total_load)
                                                / sds.total_capacity;

        /*
         * If the busiest group is imbalanced the below checks don't
         * work because they assume all things are equal, which typically
         * isn't true due to cpus_allowed constraints and the like.
         */
        if (busiest->group_type == group_imbalanced)
                goto force_balance;

        /*
         * When dst_cpu is idle, prevent SMP nice and/or asymmetric group
         * capacities from resulting in underutilization due to avg_load.
         */
        if (env->idle != CPU_NOT_IDLE && group_has_capacity(env, local) &&
            busiest->group_no_capacity)
                goto force_balance;

        /*
         * If the local group is busier than the selected busiest group
         * don't try and pull any tasks.
         */
        if (local->avg_load >= busiest->avg_load)
                goto out_balanced;

        /*
         * Don't pull any tasks if this group is already above the domain
         * average load.
         */
        if (local->avg_load >= sds.avg_load)
                goto out_balanced;

        if (env->idle == CPU_IDLE) {
                /*
                 * This CPU is idle. If the busiest group is not overloaded
                 * and there is no imbalance between this and busiest group
                 * wrt idle CPUs, it is balanced. The imbalance becomes
                 * significant if the diff is greater than 1 otherwise we
                 * might end up to just move the imbalance on another group
                 */
                if ((busiest->group_type != group_overloaded) &&
                                (local->idle_cpus <= (busiest->idle_cpus + 1)))
                        goto out_balanced;
        } else {
                /*
                 * In the CPU_NEWLY_IDLE, CPU_NOT_IDLE cases, use
                 * imbalance_pct to be conservative.
                 */
                if (100 * busiest->avg_load <=
                                env->sd->imbalance_pct * local->avg_load)
                        goto out_balanced;
        }

force_balance:
        /* Looks like there is an imbalance. Compute it */
        calculate_imbalance(env, &sds);
        return env->imbalance ? sds.busiest : NULL;

out_balanced:
        env->imbalance = 0;
        return NULL;
}

/*
 * find_busiest_queue - find the busiest runqueue among the CPUs in the group.
 */
static struct rq *find_busiest_queue(struct lb_env *env,
                                     struct sched_group *group)
{
        struct rq *busiest = NULL, *rq;
        unsigned long busiest_load = 0, busiest_capacity = 1;
        int i;

        for_each_cpu_and(i, sched_group_span(group), env->cpus) {
                unsigned long capacity, wl;
                enum fbq_type rt;

                rq = cpu_rq(i);
                rt = fbq_classify_rq(rq);

                /*
                 * We classify groups/runqueues into three groups:
                 *  - regular: there are !numa tasks
                 *  - remote:  there are numa tasks that run on the 'wrong' node
                 *  - all:     there is no distinction
                 *
                 * In order to avoid migrating ideally placed numa tasks,
                 * ignore those when there's better options.
                 *
                 * If we ignore the actual busiest queue to migrate another
                 * task, the next balance pass can still reduce the busiest
                 * queue by moving tasks around inside the node.
                 *
                 * If we cannot move enough load due to this classification
                 * the next pass will adjust the group classification and
                 * allow migration of more tasks.
                 *
                 * Both cases only affect the total convergence complexity.
                 */
                if (rt > env->fbq_type)
                        continue;

                capacity = capacity_of(i);

                wl = weighted_cpuload(rq);

                /*
                 * When comparing with imbalance, use weighted_cpuload()
                 * which is not scaled with the CPU capacity.
                 */

                if (rq->nr_running == 1 && wl > env->imbalance &&
                    !check_cpu_capacity(rq, env->sd))
                        continue;

                /*
                 * For the load comparisons with the other CPU's, consider
                 * the weighted_cpuload() scaled with the CPU capacity, so
                 * that the load can be moved away from the CPU that is
                 * potentially running at a lower capacity.
                 *
                 * Thus we're looking for max(wl_i / capacity_i), crosswise
                 * multiplication to rid ourselves of the division works out
                 * to: wl_i * capacity_j > wl_j * capacity_i;  where j is
                 * our previous maximum.
                 */
                if (wl * busiest_capacity > busiest_load * capacity) {
                        busiest_load = wl;
                        busiest_capacity = capacity;
                        busiest = rq;
                }
        }

        return busiest;
}

/*
 * Max backoff if we encounter pinned tasks. Pretty arbitrary value, but
 * so long as it is large enough.
 */
#define MAX_PINNED_INTERVAL     512

static int need_active_balance(struct lb_env *env)
{
        struct sched_domain *sd = env->sd;

        if (env->idle == CPU_NEWLY_IDLE) {

                /*
                 * ASYM_PACKING needs to force migrate tasks from busy but
                 * lower priority CPUs in order to pack all tasks in the
                 * highest priority CPUs.
                 */
                if ((sd->flags & SD_ASYM_PACKING) &&
                    sched_asym_prefer(env->dst_cpu, env->src_cpu))
                        return 1;
        }

        /*
         * The dst_cpu is idle and the src_cpu CPU has only 1 CFS task.
         * It's worth migrating the task if the src_cpu's capacity is reduced
         * because of other sched_class or IRQs if more capacity stays
         * available on dst_cpu.
         */
        if ((env->idle != CPU_NOT_IDLE) &&
            (env->src_rq->cfs.h_nr_running == 1)) {
                if ((check_cpu_capacity(env->src_rq, sd)) &&
                    (capacity_of(env->src_cpu)*sd->imbalance_pct < capacity_of(env->dst_cpu)*100))
                        return 1;
        }

        return unlikely(sd->nr_balance_failed > sd->cache_nice_tries+2);
}

static int active_load_balance_cpu_stop(void *data);

static int should_we_balance(struct lb_env *env)
{
        struct sched_group *sg = env->sd->groups;
        int cpu, balance_cpu = -1;

        /*
         * Ensure the balancing environment is consistent; can happen
         * when the softirq triggers 'during' hotplug.
         */
        if (!cpumask_test_cpu(env->dst_cpu, env->cpus))
                return 0;

        /*
         * In the newly idle case, we will allow all the CPUs
         * to do the newly idle load balance.
         */
        if (env->idle == CPU_NEWLY_IDLE)
                return 1;

        /* Try to find first idle CPU */
        for_each_cpu_and(cpu, group_balance_mask(sg), env->cpus) {
                if (!idle_cpu(cpu))
                        continue;

                balance_cpu = cpu;
                break;
        }

        if (balance_cpu == -1)
                balance_cpu = group_balance_cpu(sg);

        /*
         * First idle CPU or the first CPU(busiest) in this sched group
         * is eligible for doing load balancing at this and above domains.
         */
        return balance_cpu == env->dst_cpu;
}

/*
 * Check this_cpu to ensure it is balanced within domain. Attempt to move
 * tasks if there is an imbalance.
 */
static int load_balance(int this_cpu, struct rq *this_rq,
                        struct sched_domain *sd, enum cpu_idle_type idle,
                        int *continue_balancing)
{
        int ld_moved, cur_ld_moved, active_balance = 0;
        struct sched_domain *sd_parent = sd->parent;
        struct sched_group *group;
        struct rq *busiest;
        struct rq_flags rf;
        struct cpumask *cpus = this_cpu_cpumask_var_ptr(load_balance_mask);

        struct lb_env env = {
                .sd             = sd,
                .dst_cpu        = this_cpu,
                .dst_rq         = this_rq,
                .dst_grpmask    = sched_group_span(sd->groups),
                .idle           = idle,
                .loop_break     = sched_nr_migrate_break,
                .cpus           = cpus,
                .fbq_type       = all,
                .tasks          = LIST_HEAD_INIT(env.tasks),
        };

        cpumask_and(cpus, sched_domain_span(sd), cpu_active_mask);

        schedstat_inc(sd->lb_count[idle]);

redo:
        if (!should_we_balance(&env)) {
                *continue_balancing = 0;
                goto out_balanced;
        }

        group = find_busiest_group(&env);
        if (!group) {
                schedstat_inc(sd->lb_nobusyg[idle]);
                goto out_balanced;
        }

        busiest = find_busiest_queue(&env, group);
        if (!busiest) {
                schedstat_inc(sd->lb_nobusyq[idle]);
                goto out_balanced;
        }

        BUG_ON(busiest == env.dst_rq);

        schedstat_add(sd->lb_imbalance[idle], env.imbalance);

        env.src_cpu = busiest->cpu;
        env.src_rq = busiest;

        ld_moved = 0;
        if (busiest->nr_running > 1) {
                /*
                 * Attempt to move tasks. If find_busiest_group has found
                 * an imbalance but busiest->nr_running <= 1, the group is
                 * still unbalanced. ld_moved simply stays zero, so it is
                 * correctly treated as an imbalance.
                 */
                env.flags |= LBF_ALL_PINNED;
                env.loop_max  = min(sysctl_sched_nr_migrate, busiest->nr_running);

more_balance:
                rq_lock_irqsave(busiest, &rf);
                update_rq_clock(busiest);

                /*
                 * cur_ld_moved - load moved in current iteration
                 * ld_moved     - cumulative load moved across iterations
                 */
                cur_ld_moved = detach_tasks(&env);

                /*
                 * We've detached some tasks from busiest_rq. Every
                 * task is masked "TASK_ON_RQ_MIGRATING", so we can safely
                 * unlock busiest->lock, and we are able to be sure
                 * that nobody can manipulate the tasks in parallel.
                 * See task_rq_lock() family for the details.
                 */

                rq_unlock(busiest, &rf);

                if (cur_ld_moved) {
                        attach_tasks(&env);
                        ld_moved += cur_ld_moved;
                }

                local_irq_restore(rf.flags);

                if (env.flags & LBF_NEED_BREAK) {
                        env.flags &= ~LBF_NEED_BREAK;
                        goto more_balance;
                }

                /*
                 * Revisit (affine) tasks on src_cpu that couldn't be moved to
                 * us and move them to an alternate dst_cpu in our sched_group
                 * where they can run. The upper limit on how many times we
                 * iterate on same src_cpu is dependent on number of CPUs in our
                 * sched_group.
                 *
                 * This changes load balance semantics a bit on who can move
                 * load to a given_cpu. In addition to the given_cpu itself
                 * (or a ilb_cpu acting on its behalf where given_cpu is
                 * nohz-idle), we now have balance_cpu in a position to move
                 * load to given_cpu. In rare situations, this may cause
                 * conflicts (balance_cpu and given_cpu/ilb_cpu deciding
                 * _independently_ and at _same_ time to move some load to
                 * given_cpu) causing exceess load to be moved to given_cpu.
                 * This however should not happen so much in practice and
                 * moreover subsequent load balance cycles should correct the
                 * excess load moved.
                 */
                if ((env.flags & LBF_DST_PINNED) && env.imbalance > 0) {

                        /* Prevent to re-select dst_cpu via env's CPUs */
                        cpumask_clear_cpu(env.dst_cpu, env.cpus);

                        env.dst_rq       = cpu_rq(env.new_dst_cpu);
                        env.dst_cpu      = env.new_dst_cpu;
                        env.flags       &= ~LBF_DST_PINNED;
                        env.loop         = 0;
                        env.loop_break   = sched_nr_migrate_break;

                        /*
                         * Go back to "more_balance" rather than "redo" since we
                         * need to continue with same src_cpu.
                         */
                        goto more_balance;
                }

                /*
                 * We failed to reach balance because of affinity.
                 */
                if (sd_parent) {
                        int *group_imbalance = &sd_parent->groups->sgc->imbalance;

                        if ((env.flags & LBF_SOME_PINNED) && env.imbalance > 0)
                                *group_imbalance = 1;
                }

                /* All tasks on this runqueue were pinned by CPU affinity */
                if (unlikely(env.flags & LBF_ALL_PINNED)) {
                        cpumask_clear_cpu(cpu_of(busiest), cpus);
                        /*
                         * Attempting to continue load balancing at the current
                         * sched_domain level only makes sense if there are
                         * active CPUs remaining as possible busiest CPUs to
                         * pull load from which are not contained within the
                         * destination group that is receiving any migrated
                         * load.
                         */
                        if (!cpumask_subset(cpus, env.dst_grpmask)) {
                                env.loop = 0;
                                env.loop_break = sched_nr_migrate_break;
                                goto redo;
                        }
                        goto out_all_pinned;
                }
        }

        if (!ld_moved) {
                schedstat_inc(sd->lb_failed[idle]);
                /*
                 * Increment the failure counter only on periodic balance.
                 * We do not want newidle balance, which can be very
                 * frequent, pollute the failure counter causing
                 * excessive cache_hot migrations and active balances.
                 */
                if (idle != CPU_NEWLY_IDLE)
                        sd->nr_balance_failed++;

                if (need_active_balance(&env)) {
                        unsigned long flags;

                        raw_spin_lock_irqsave(&busiest->lock, flags);

                        /*
                         * Don't kick the active_load_balance_cpu_stop,
                         * if the curr task on busiest CPU can't be
                         * moved to this_cpu:
                         */
                        if (!cpumask_test_cpu(this_cpu, &busiest->curr->cpus_allowed)) {
                                raw_spin_unlock_irqrestore(&busiest->lock,
                                                            flags);
                                env.flags |= LBF_ALL_PINNED;
                                goto out_one_pinned;
                        }

                        /*
                         * ->active_balance synchronizes accesses to
                         * ->active_balance_work.  Once set, it's cleared
                         * only after active load balance is finished.
                         */
                        if (!busiest->active_balance) {
                                busiest->active_balance = 1;
                                busiest->push_cpu = this_cpu;
                                active_balance = 1;
                        }
                        raw_spin_unlock_irqrestore(&busiest->lock, flags);

                        if (active_balance) {
                                stop_one_cpu_nowait(cpu_of(busiest),
                                        active_load_balance_cpu_stop, busiest,
                                        &busiest->active_balance_work);
                        }

                        /* We've kicked active balancing, force task migration. */
                        sd->nr_balance_failed = sd->cache_nice_tries+1;
                }
        } else
                sd->nr_balance_failed = 0;

        if (likely(!active_balance)) {
                /* We were unbalanced, so reset the balancing interval */
                sd->balance_interval = sd->min_interval;
        } else {
                /*
                 * If we've begun active balancing, start to back off. This
                 * case may not be covered by the all_pinned logic if there
                 * is only 1 task on the busy runqueue (because we don't call
                 * detach_tasks).
                 */
                if (sd->balance_interval < sd->max_interval)
                        sd->balance_interval *= 2;
        }

        goto out;

out_balanced:
        /*
         * We reach balance although we may have faced some affinity
         * constraints. Clear the imbalance flag if it was set.
         */
        if (sd_parent) {
                int *group_imbalance = &sd_parent->groups->sgc->imbalance;

                if (*group_imbalance)
                        *group_imbalance = 0;
        }

out_all_pinned:
        /*
         * We reach balance because all tasks are pinned at this level so
         * we can't migrate them. Let the imbalance flag set so parent level
         * can try to migrate them.
         */
        schedstat_inc(sd->lb_balanced[idle]);

        sd->nr_balance_failed = 0;

out_one_pinned:
        /* tune up the balancing interval */
        if (((env.flags & LBF_ALL_PINNED) &&
                        sd->balance_interval < MAX_PINNED_INTERVAL) ||
                        (sd->balance_interval < sd->max_interval))
                sd->balance_interval *= 2;

        ld_moved = 0;
out:
        return ld_moved;
}

static inline unsigned long
get_sd_balance_interval(struct sched_domain *sd, int cpu_busy)
{
        unsigned long interval = sd->balance_interval;

        if (cpu_busy)
                interval *= sd->busy_factor;

        /* scale ms to jiffies */
        interval = msecs_to_jiffies(interval);
        interval = clamp(interval, 1UL, max_load_balance_interval);

        return interval;
}

static inline void
update_next_balance(struct sched_domain *sd, unsigned long *next_balance)
{
        unsigned long interval, next;

        /* used by idle balance, so cpu_busy = 0 */
        interval = get_sd_balance_interval(sd, 0);
        next = sd->last_balance + interval;

        if (time_after(*next_balance, next))
                *next_balance = next;
}

/*
 * active_load_balance_cpu_stop is run by the CPU stopper. It pushes
 * running tasks off the busiest CPU onto idle CPUs. It requires at
 * least 1 task to be running on each physical CPU where possible, and
 * avoids physical / logical imbalances.
 */
static int active_load_balance_cpu_stop(void *data)
{
        struct rq *busiest_rq = data;
        int busiest_cpu = cpu_of(busiest_rq);
        int target_cpu = busiest_rq->push_cpu;
        struct rq *target_rq = cpu_rq(target_cpu);
        struct sched_domain *sd;
        struct task_struct *p = NULL;
        struct rq_flags rf;

        rq_lock_irq(busiest_rq, &rf);
        /*
         * Between queueing the stop-work and running it is a hole in which
         * CPUs can become inactive. We should not move tasks from or to
         * inactive CPUs.
         */
        if (!cpu_active(busiest_cpu) || !cpu_active(target_cpu))
                goto out_unlock;

        /* Make sure the requested CPU hasn't gone down in the meantime: */
        if (unlikely(busiest_cpu != smp_processor_id() ||
                     !busiest_rq->active_balance))
                goto out_unlock;

        /* Is there any task to move? */
        if (busiest_rq->nr_running <= 1)
                goto out_unlock;

        /*
         * This condition is "impossible", if it occurs
         * we need to fix it. Originally reported by
         * Bjorn Helgaas on a 128-CPU setup.
         */
        BUG_ON(busiest_rq == target_rq);

        /* Search for an sd spanning us and the target CPU. */
        rcu_read_lock();
        for_each_domain(target_cpu, sd) {
                if ((sd->flags & SD_LOAD_BALANCE) &&
                    cpumask_test_cpu(busiest_cpu, sched_domain_span(sd)))
                                break;
        }

        if (likely(sd)) {
                struct lb_env env = {
                        .sd             = sd,
                        .dst_cpu        = target_cpu,
                        .dst_rq         = target_rq,
                        .src_cpu        = busiest_rq->cpu,
                        .src_rq         = busiest_rq,
                        .idle           = CPU_IDLE,
                        /*
                         * can_migrate_task() doesn't need to compute new_dst_cpu
                         * for active balancing. Since we have CPU_IDLE, but no
                         * @dst_grpmask we need to make that test go away with lying
                         * about DST_PINNED.
                         */
                        .flags          = LBF_DST_PINNED,
                };

                schedstat_inc(sd->alb_count);
                update_rq_clock(busiest_rq);

                p = detach_one_task(&env);
                if (p) {
                        schedstat_inc(sd->alb_pushed);
                        /* Active balancing done, reset the failure counter. */
                        sd->nr_balance_failed = 0;
                } else {
                        schedstat_inc(sd->alb_failed);
                }
        }
        rcu_read_unlock();
out_unlock:
        busiest_rq->active_balance = 0;
        rq_unlock(busiest_rq, &rf);

        if (p)
                attach_one_task(target_rq, p);

        local_irq_enable();

        return 0;
}

static DEFINE_SPINLOCK(balancing);

/*
 * Scale the max load_balance interval with the number of CPUs in the system.
 * This trades load-balance latency on larger machines for less cross talk.
 */
void update_max_interval(void)
{
        max_load_balance_interval = HZ*num_online_cpus()/10;
}

/*
 * It checks each scheduling domain to see if it is due to be balanced,
 * and initiates a balancing operation if so.
 *
 * Balancing parameters are set up in init_sched_domains.
 */
static void rebalance_domains(struct rq *rq, enum cpu_idle_type idle)
{
        int continue_balancing = 1;
        int cpu = rq->cpu;
        unsigned long interval;
        struct sched_domain *sd;
        /* Earliest time when we have to do rebalance again */
        unsigned long next_balance = jiffies + 60*HZ;
        int update_next_balance = 0;
        int need_serialize, need_decay = 0;
        u64 max_cost = 0;

        rcu_read_lock();
        for_each_domain(cpu, sd) {
                /*
                 * Decay the newidle max times here because this is a regular
                 * visit to all the domains. Decay ~1% per second.
                 */
                if (time_after(jiffies, sd->next_decay_max_lb_cost)) {
                        sd->max_newidle_lb_cost =
                                (sd->max_newidle_lb_cost * 253) / 256;
                        sd->next_decay_max_lb_cost = jiffies + HZ;
                        need_decay = 1;
                }
                max_cost += sd->max_newidle_lb_cost;

                if (!(sd->flags & SD_LOAD_BALANCE))
                        continue;

                /*
                 * Stop the load balance at this level. There is another
                 * CPU in our sched group which is doing load balancing more
                 * actively.
                 */
                if (!continue_balancing) {
                        if (need_decay)
                                continue;
                        break;
                }

                interval = get_sd_balance_interval(sd, idle != CPU_IDLE);

                need_serialize = sd->flags & SD_SERIALIZE;
                if (need_serialize) {
                        if (!spin_trylock(&balancing))
                                goto out;
                }

                if (time_after_eq(jiffies, sd->last_balance + interval)) {
                        if (load_balance(cpu, rq, sd, idle, &continue_balancing)) {
                                /*
                                 * The LBF_DST_PINNED logic could have changed
                                 * env->dst_cpu, so we can't know our idle
                                 * state even if we migrated tasks. Update it.
                                 */
                                idle = idle_cpu(cpu) ? CPU_IDLE : CPU_NOT_IDLE;
                        }
                        sd->last_balance = jiffies;
                        interval = get_sd_balance_interval(sd, idle != CPU_IDLE);
                }
                if (need_serialize)
                        spin_unlock(&balancing);
out:
                if (time_after(next_balance, sd->last_balance + interval)) {
                        next_balance = sd->last_balance + interval;
                        update_next_balance = 1;
                }
        }
        if (need_decay) {
                /*
                 * Ensure the rq-wide value also decays but keep it at a
                 * reasonable floor to avoid funnies with rq->avg_idle.
                 */
                rq->max_idle_balance_cost =
                        max((u64)sysctl_sched_migration_cost, max_cost);
        }
        rcu_read_unlock();

        /*
         * next_balance will be updated only when there is a need.
         * When the cpu is attached to null domain for ex, it will not be
         * updated.
         */
        if (likely(update_next_balance)) {
                rq->next_balance = next_balance;

#ifdef CONFIG_NO_HZ_COMMON
                /*
                 * If this CPU has been elected to perform the nohz idle
                 * balance. Other idle CPUs have already rebalanced with
                 * nohz_idle_balance() and nohz.next_balance has been
                 * updated accordingly. This CPU is now running the idle load
                 * balance for itself and we need to update the
                 * nohz.next_balance accordingly.
                 */
                if ((idle == CPU_IDLE) && time_after(nohz.next_balance, rq->next_balance))
                        nohz.next_balance = rq->next_balance;
#endif
        }
}

static inline int on_null_domain(struct rq *rq)
{
        return unlikely(!rcu_dereference_sched(rq->sd));
}

#ifdef CONFIG_NO_HZ_COMMON
/*
 * idle load balancing details
 * - When one of the busy CPUs notice that there may be an idle rebalancing
 *   needed, they will kick the idle load balancer, which then does idle
 *   load balancing for all the idle CPUs.
 */

static inline int find_new_ilb(void)
{
        int ilb = cpumask_first(nohz.idle_cpus_mask);

        if (ilb < nr_cpu_ids && idle_cpu(ilb))
                return ilb;

        return nr_cpu_ids;
}

/*
 * Kick a CPU to do the nohz balancing, if it is time for it. We pick the
 * nohz_load_balancer CPU (if there is one) otherwise fallback to any idle
 * CPU (if there is one).
 */
static void kick_ilb(unsigned int flags)
{
        int ilb_cpu;

        nohz.next_balance++;

        ilb_cpu = find_new_ilb();

        if (ilb_cpu >= nr_cpu_ids)
                return;

        flags = atomic_fetch_or(flags, nohz_flags(ilb_cpu));
        if (flags & NOHZ_KICK_MASK)
                return;

        /*
         * Use smp_send_reschedule() instead of resched_cpu().
         * This way we generate a sched IPI on the target CPU which
         * is idle. And the softirq performing nohz idle load balance
         * will be run before returning from the IPI.
         */
        smp_send_reschedule(ilb_cpu);
}

/*
 * Current heuristic for kicking the idle load balancer in the presence
 * of an idle cpu in the system.
 *   - This rq has more than one task.
 *   - This rq has at least one CFS task and the capacity of the CPU is
 *     significantly reduced because of RT tasks or IRQs.
 *   - At parent of LLC scheduler domain level, this cpu's scheduler group has
 *     multiple busy cpu.
 *   - For SD_ASYM_PACKING, if the lower numbered cpu's in the scheduler
 *     domain span are idle.
 */
static void nohz_balancer_kick(struct rq *rq)
{
        unsigned long now = jiffies;
        struct sched_domain_shared *sds;
        struct sched_domain *sd;
        int nr_busy, i, cpu = rq->cpu;
        unsigned int flags = 0;

        if (unlikely(rq->idle_balance))
                return;

        /*
         * We may be recently in ticked or tickless idle mode. At the first
         * busy tick after returning from idle, we will update the busy stats.
         */
        nohz_balance_exit_idle(rq);

        /*
         * None are in tickless mode and hence no need for NOHZ idle load
         * balancing.
         */
        if (likely(!atomic_read(&nohz.nr_cpus)))
                return;

        if (READ_ONCE(nohz.has_blocked) &&
            time_after(now, READ_ONCE(nohz.next_blocked)))
                flags = NOHZ_STATS_KICK;

        if (time_before(now, nohz.next_balance))
                goto out;

        if (rq->nr_running >= 2) {
                flags = NOHZ_KICK_MASK;
                goto out;
        }

        rcu_read_lock();
        sds = rcu_dereference(per_cpu(sd_llc_shared, cpu));
        if (sds) {
                /*
                 * XXX: write a coherent comment on why we do this.
                 * See also: http://lkml.kernel.org/r/20111202010832.602203411@sbsiddha-desk.sc.intel.com
                 */
                nr_busy = atomic_read(&sds->nr_busy_cpus);
                if (nr_busy > 1) {
                        flags = NOHZ_KICK_MASK;
                        goto unlock;
                }

        }

        sd = rcu_dereference(rq->sd);
        if (sd) {
                if ((rq->cfs.h_nr_running >= 1) &&
                                check_cpu_capacity(rq, sd)) {
                        flags = NOHZ_KICK_MASK;
                        goto unlock;
                }
        }

        sd = rcu_dereference(per_cpu(sd_asym, cpu));
        if (sd) {
                for_each_cpu(i, sched_domain_span(sd)) {
                        if (i == cpu ||
                            !cpumask_test_cpu(i, nohz.idle_cpus_mask))
                                continue;

                        if (sched_asym_prefer(i, cpu)) {
                                flags = NOHZ_KICK_MASK;
                                goto unlock;
                        }
                }
        }
unlock:
        rcu_read_unlock();
out:
        if (flags)
                kick_ilb(flags);
}

static void set_cpu_sd_state_busy(int cpu)
{
        struct sched_domain *sd;

        rcu_read_lock();
        sd = rcu_dereference(per_cpu(sd_llc, cpu));

        if (!sd || !sd->nohz_idle)
                goto unlock;
        sd->nohz_idle = 0;

        atomic_inc(&sd->shared->nr_busy_cpus);
unlock:
        rcu_read_unlock();
}

void nohz_balance_exit_idle(struct rq *rq)
{
        SCHED_WARN_ON(rq != this_rq());

        if (likely(!rq->nohz_tick_stopped))
                return;

        rq->nohz_tick_stopped = 0;
        cpumask_clear_cpu(rq->cpu, nohz.idle_cpus_mask);
        atomic_dec(&nohz.nr_cpus);

        set_cpu_sd_state_busy(rq->cpu);
}

static void set_cpu_sd_state_idle(int cpu)
{
        struct sched_domain *sd;

        rcu_read_lock();
        sd = rcu_dereference(per_cpu(sd_llc, cpu));

        if (!sd || sd->nohz_idle)
                goto unlock;
        sd->nohz_idle = 1;

        atomic_dec(&sd->shared->nr_busy_cpus);
unlock:
        rcu_read_unlock();
}

/*
 * This routine will record that the CPU is going idle with tick stopped.
 * This info will be used in performing idle load balancing in the future.
 */
void nohz_balance_enter_idle(int cpu)
{
        struct rq *rq = cpu_rq(cpu);

        SCHED_WARN_ON(cpu != smp_processor_id());

        /* If this CPU is going down, then nothing needs to be done: */
        if (!cpu_active(cpu))
                return;

        /* Spare idle load balancing on CPUs that don't want to be disturbed: */
        if (!housekeeping_cpu(cpu, HK_FLAG_SCHED))
                return;

        /*
         * Can be set safely without rq->lock held
         * If a clear happens, it will have evaluated last additions because
         * rq->lock is held during the check and the clear
         */
        rq->has_blocked_load = 1;

        /*
         * The tick is still stopped but load could have been added in the
         * meantime. We set the nohz.has_blocked flag to trig a check of the
         * *_avg. The CPU is already part of nohz.idle_cpus_mask so the clear
         * of nohz.has_blocked can only happen after checking the new load
         */
        if (rq->nohz_tick_stopped)
                goto out;

        /* If we're a completely isolated CPU, we don't play: */
        if (on_null_domain(rq))
                return;

        rq->nohz_tick_stopped = 1;

        cpumask_set_cpu(cpu, nohz.idle_cpus_mask);
        atomic_inc(&nohz.nr_cpus);

        /*
         * Ensures that if nohz_idle_balance() fails to observe our
         * @idle_cpus_mask store, it must observe the @has_blocked
         * store.
         */
        smp_mb__after_atomic();

        set_cpu_sd_state_idle(cpu);

out:
        /*
         * Each time a cpu enter idle, we assume that it has blocked load and
         * enable the periodic update of the load of idle cpus
         */
        WRITE_ONCE(nohz.has_blocked, 1);
}

/*
 * Internal function that runs load balance for all idle cpus. The load balance
 * can be a simple update of blocked load or a complete load balance with
 * tasks movement depending of flags.
 * The function returns false if the loop has stopped before running
 * through all idle CPUs.
 */
static bool _nohz_idle_balance(struct rq *this_rq, unsigned int flags,
                               enum cpu_idle_type idle)
{
        /* Earliest time when we have to do rebalance again */
        unsigned long now = jiffies;
        unsigned long next_balance = now + 60*HZ;
        bool has_blocked_load = false;
        int update_next_balance = 0;
        int this_cpu = this_rq->cpu;
        int balance_cpu;
        int ret = false;
        struct rq *rq;

        SCHED_WARN_ON((flags & NOHZ_KICK_MASK) == NOHZ_BALANCE_KICK);

        /*
         * We assume there will be no idle load after this update and clear
         * the has_blocked flag. If a cpu enters idle in the mean time, it will
         * set the has_blocked flag and trig another update of idle load.
         * Because a cpu that becomes idle, is added to idle_cpus_mask before
         * setting the flag, we are sure to not clear the state and not
         * check the load of an idle cpu.
         */
        WRITE_ONCE(nohz.has_blocked, 0);

        /*
         * Ensures that if we miss the CPU, we must see the has_blocked
         * store from nohz_balance_enter_idle().
         */
        smp_mb();

        for_each_cpu(balance_cpu, nohz.idle_cpus_mask) {
                if (balance_cpu == this_cpu || !idle_cpu(balance_cpu))
                        continue;

                /*
                 * If this CPU gets work to do, stop the load balancing
                 * work being done for other CPUs. Next load
                 * balancing owner will pick it up.
                 */
                if (need_resched()) {
                        has_blocked_load = true;
                        goto abort;
                }

                rq = cpu_rq(balance_cpu);

                has_blocked_load |= update_nohz_stats(rq, true);

                /*
                 * If time for next balance is due,
                 * do the balance.
                 */
                if (time_after_eq(jiffies, rq->next_balance)) {
                        struct rq_flags rf;

                        rq_lock_irqsave(rq, &rf);
                        update_rq_clock(rq);
                        cpu_load_update_idle(rq);
                        rq_unlock_irqrestore(rq, &rf);

                        if (flags & NOHZ_BALANCE_KICK)
                                rebalance_domains(rq, CPU_IDLE);
                }

                if (time_after(next_balance, rq->next_balance)) {
                        next_balance = rq->next_balance;
                        update_next_balance = 1;
                }
        }

        /* Newly idle CPU doesn't need an update */
        if (idle != CPU_NEWLY_IDLE) {
                update_blocked_averages(this_cpu);
                has_blocked_load |= this_rq->has_blocked_load;
        }

        if (flags & NOHZ_BALANCE_KICK)
                rebalance_domains(this_rq, CPU_IDLE);

        WRITE_ONCE(nohz.next_blocked,
                now + msecs_to_jiffies(LOAD_AVG_PERIOD));

        /* The full idle balance loop has been done */
        ret = true;

abort:
        /* There is still blocked load, enable periodic update */
        if (has_blocked_load)
                WRITE_ONCE(nohz.has_blocked, 1);

        /*
         * next_balance will be updated only when there is a need.
         * When the CPU is attached to null domain for ex, it will not be
         * updated.
         */
        if (likely(update_next_balance))
                nohz.next_balance = next_balance;

        return ret;
}

/*
 * In CONFIG_NO_HZ_COMMON case, the idle balance kickee will do the
 * rebalancing for all the cpus for whom scheduler ticks are stopped.
 */
static bool nohz_idle_balance(struct rq *this_rq, enum cpu_idle_type idle)
{
        int this_cpu = this_rq->cpu;
        unsigned int flags;

        if (!(atomic_read(nohz_flags(this_cpu)) & NOHZ_KICK_MASK))
                return false;

        if (idle != CPU_IDLE) {
                atomic_andnot(NOHZ_KICK_MASK, nohz_flags(this_cpu));
                return false;
        }

        /*
         * barrier, pairs with nohz_balance_enter_idle(), ensures ...
         */
        flags = atomic_fetch_andnot(NOHZ_KICK_MASK, nohz_flags(this_cpu));
        if (!(flags & NOHZ_KICK_MASK))
                return false;

        _nohz_idle_balance(this_rq, flags, idle);

        return true;
}

static void nohz_newidle_balance(struct rq *this_rq)
{
        int this_cpu = this_rq->cpu;

        /*
         * This CPU doesn't want to be disturbed by scheduler
         * housekeeping
         */
        if (!housekeeping_cpu(this_cpu, HK_FLAG_SCHED))
                return;

        /* Will wake up very soon. No time for doing anything else*/
        if (this_rq->avg_idle < sysctl_sched_migration_cost)
                return;

        /* Don't need to update blocked load of idle CPUs*/
        if (!READ_ONCE(nohz.has_blocked) ||
            time_before(jiffies, READ_ONCE(nohz.next_blocked)))
                return;

        raw_spin_unlock(&this_rq->lock);
        /*
         * This CPU is going to be idle and blocked load of idle CPUs
         * need to be updated. Run the ilb locally as it is a good
         * candidate for ilb instead of waking up another idle CPU.
         * Kick an normal ilb if we failed to do the update.
         */
        if (!_nohz_idle_balance(this_rq, NOHZ_STATS_KICK, CPU_NEWLY_IDLE))
                kick_ilb(NOHZ_STATS_KICK);
        raw_spin_lock(&this_rq->lock);
}

#else /* !CONFIG_NO_HZ_COMMON */
static inline void nohz_balancer_kick(struct rq *rq) { }

static inline bool nohz_idle_balance(struct rq *this_rq, enum cpu_idle_type idle)
{
        return false;
}

static inline void nohz_newidle_balance(struct rq *this_rq) { }
#endif /* CONFIG_NO_HZ_COMMON */

/*
 * idle_balance is called by schedule() if this_cpu is about to become
 * idle. Attempts to pull tasks from other CPUs.
 */
static int idle_balance(struct rq *this_rq, struct rq_flags *rf)
{
        unsigned long next_balance = jiffies + HZ;
        int this_cpu = this_rq->cpu;
        struct sched_domain *sd;
        int pulled_task = 0;
        u64 curr_cost = 0;

        /*
         * We must set idle_stamp _before_ calling idle_balance(), such that we
         * measure the duration of idle_balance() as idle time.
         */
        this_rq->idle_stamp = rq_clock(this_rq);

        /*
         * Do not pull tasks towards !active CPUs...
         */
        if (!cpu_active(this_cpu))
                return 0;

        /*
         * This is OK, because current is on_cpu, which avoids it being picked
         * for load-balance and preemption/IRQs are still disabled avoiding
         * further scheduler activity on it and we're being very careful to
         * re-start the picking loop.
         */
        rq_unpin_lock(this_rq, rf);

        if (this_rq->avg_idle < sysctl_sched_migration_cost ||
            !this_rq->rd->overload) {

                rcu_read_lock();
                sd = rcu_dereference_check_sched_domain(this_rq->sd);
                if (sd)
                        update_next_balance(sd, &next_balance);
                rcu_read_unlock();

                nohz_newidle_balance(this_rq);

                goto out;
        }

        raw_spin_unlock(&this_rq->lock);

        update_blocked_averages(this_cpu);
        rcu_read_lock();
        for_each_domain(this_cpu, sd) {
                int continue_balancing = 1;
                u64 t0, domain_cost;

                if (!(sd->flags & SD_LOAD_BALANCE))
                        continue;

                if (this_rq->avg_idle < curr_cost + sd->max_newidle_lb_cost) {
                        update_next_balance(sd, &next_balance);
                        break;
                }

                if (sd->flags & SD_BALANCE_NEWIDLE) {
                        t0 = sched_clock_cpu(this_cpu);

                        pulled_task = load_balance(this_cpu, this_rq,
                                                   sd, CPU_NEWLY_IDLE,
                                                   &continue_balancing);

                        domain_cost = sched_clock_cpu(this_cpu) - t0;
                        if (domain_cost > sd->max_newidle_lb_cost)
                                sd->max_newidle_lb_cost = domain_cost;

                        curr_cost += domain_cost;
                }

                update_next_balance(sd, &next_balance);

                /*
                 * Stop searching for tasks to pull if there are
                 * now runnable tasks on this rq.
                 */
                if (pulled_task || this_rq->nr_running > 0)
                        break;
        }
        rcu_read_unlock();

        raw_spin_lock(&this_rq->lock);

        if (curr_cost > this_rq->max_idle_balance_cost)
                this_rq->max_idle_balance_cost = curr_cost;

out:
        /*
         * While browsing the domains, we released the rq lock, a task could
         * have been enqueued in the meantime. Since we're not going idle,
         * pretend we pulled a task.
         */
        if (this_rq->cfs.h_nr_running && !pulled_task)
                pulled_task = 1;

        /* Move the next balance forward */
        if (time_after(this_rq->next_balance, next_balance))
                this_rq->next_balance = next_balance;

        /* Is there a task of a high priority class? */
        if (this_rq->nr_running != this_rq->cfs.h_nr_running)
                pulled_task = -1;

        if (pulled_task)
                this_rq->idle_stamp = 0;

        rq_repin_lock(this_rq, rf);

        return pulled_task;
}

/*
 * run_rebalance_domains is triggered when needed from the scheduler tick.
 * Also triggered for nohz idle balancing (with nohz_balancing_kick set).
 */
static __latent_entropy void run_rebalance_domains(struct softirq_action *h)
{
        struct rq *this_rq = this_rq();
        enum cpu_idle_type idle = this_rq->idle_balance ?
                                                CPU_IDLE : CPU_NOT_IDLE;

        /*
         * If this CPU has a pending nohz_balance_kick, then do the
         * balancing on behalf of the other idle CPUs whose ticks are
         * stopped. Do nohz_idle_balance *before* rebalance_domains to
         * give the idle CPUs a chance to load balance. Else we may
         * load balance only within the local sched_domain hierarchy
         * and abort nohz_idle_balance altogether if we pull some load.
         */
        if (nohz_idle_balance(this_rq, idle))
                return;

        /* normal load balance */
        update_blocked_averages(this_rq->cpu);
        rebalance_domains(this_rq, idle);
}

/*
 * Trigger the SCHED_SOFTIRQ if it is time to do periodic load balancing.
 */
void trigger_load_balance(struct rq *rq)
{
        /* Don't need to rebalance while attached to NULL domain */
        if (unlikely(on_null_domain(rq)))
                return;

        if (time_after_eq(jiffies, rq->next_balance))
                raise_softirq(SCHED_SOFTIRQ);

        nohz_balancer_kick(rq);
}

static void rq_online_fair(struct rq *rq)
{
        update_sysctl();

        update_runtime_enabled(rq);
}

static void rq_offline_fair(struct rq *rq)
{
        update_sysctl();

        /* Ensure any throttled groups are reachable by pick_next_task */
        unthrottle_offline_cfs_rqs(rq);
}

#endif /* CONFIG_SMP */

/*
 * scheduler tick hitting a task of our scheduling class.
 *
 * NOTE: This function can be called remotely by the tick offload that
 * goes along full dynticks. Therefore no local assumption can be made
 * and everything must be accessed through the @rq and @curr passed in
 * parameters.
 */
static void task_tick_fair(struct rq *rq, struct task_struct *curr, int queued)
{
        struct cfs_rq *cfs_rq;
        struct sched_entity *se = &curr->se;

        for_each_sched_entity(se) {
                cfs_rq = cfs_rq_of(se);
                entity_tick(cfs_rq, se, queued);
        }

        if (static_branch_unlikely(&sched_numa_balancing))
                task_tick_numa(rq, curr);
}

/*
 * called on fork with the child task as argument from the parent's context
 *  - child not yet on the tasklist
 *  - preemption disabled
 */
static void task_fork_fair(struct task_struct *p)
{
        struct cfs_rq *cfs_rq;
        struct sched_entity *se = &p->se, *curr;
        struct rq *rq = this_rq();
        struct rq_flags rf;

        rq_lock(rq, &rf);
        update_rq_clock(rq);

        cfs_rq = task_cfs_rq(current);
        curr = cfs_rq->curr;
        if (curr) {
                update_curr(cfs_rq);
                se->vruntime = curr->vruntime;
        }
        place_entity(cfs_rq, se, 1);

        if (sysctl_sched_child_runs_first && curr && entity_before(curr, se)) {
                /*
                 * Upon rescheduling, sched_class::put_prev_task() will place
                 * 'current' within the tree based on its new key value.
                 */
                swap(curr->vruntime, se->vruntime);
                resched_curr(rq);
        }

        se->vruntime -= cfs_rq->min_vruntime;
        rq_unlock(rq, &rf);
}

/*
 * Priority of the task has changed. Check to see if we preempt
 * the current task.
 */
static void
prio_changed_fair(struct rq *rq, struct task_struct *p, int oldprio)
{
        if (!task_on_rq_queued(p))
                return;

        /*
         * Reschedule if we are currently running on this runqueue and
         * our priority decreased, or if we are not currently running on
         * this runqueue and our priority is higher than the current's
         */
        if (rq->curr == p) {
                if (p->prio > oldprio)
                        resched_curr(rq);
        } else
                check_preempt_curr(rq, p, 0);
}

static inline bool vruntime_normalized(struct task_struct *p)
{
        struct sched_entity *se = &p->se;

        /*
         * In both the TASK_ON_RQ_QUEUED and TASK_ON_RQ_MIGRATING cases,
         * the dequeue_entity(.flags=0) will already have normalized the
         * vruntime.
         */
        if (p->on_rq)
                return true;

        /*
         * When !on_rq, vruntime of the task has usually NOT been normalized.
         * But there are some cases where it has already been normalized:
         *
         * - A forked child which is waiting for being woken up by
         *   wake_up_new_task().
         * - A task which has been woken up by try_to_wake_up() and
         *   waiting for actually being woken up by sched_ttwu_pending().
         */
        if (!se->sum_exec_runtime ||
            (p->state == TASK_WAKING && p->sched_remote_wakeup))
                return true;

        return false;
}

#ifdef CONFIG_FAIR_GROUP_SCHED
/*
 * Propagate the changes of the sched_entity across the tg tree to make it
 * visible to the root
 */
static void propagate_entity_cfs_rq(struct sched_entity *se)
{
        struct cfs_rq *cfs_rq;

        /* Start to propagate at parent */
        se = se->parent;

        for_each_sched_entity(se) {
                cfs_rq = cfs_rq_of(se);

                if (cfs_rq_throttled(cfs_rq))
                        break;

                update_load_avg(cfs_rq, se, UPDATE_TG);
        }
}
#else
static void propagate_entity_cfs_rq(struct sched_entity *se) { }
#endif

static void detach_entity_cfs_rq(struct sched_entity *se)
{
        struct cfs_rq *cfs_rq = cfs_rq_of(se);

        /* Catch up with the cfs_rq and remove our load when we leave */
        update_load_avg(cfs_rq, se, 0);
        detach_entity_load_avg(cfs_rq, se);
        update_tg_load_avg(cfs_rq, false);
        propagate_entity_cfs_rq(se);
}

static void attach_entity_cfs_rq(struct sched_entity *se)
{
        struct cfs_rq *cfs_rq = cfs_rq_of(se);

#ifdef CONFIG_FAIR_GROUP_SCHED
        /*
         * Since the real-depth could have been changed (only FAIR
         * class maintain depth value), reset depth properly.
         */
        se->depth = se->parent ? se->parent->depth + 1 : 0;
#endif

        /* Synchronize entity with its cfs_rq */
        update_load_avg(cfs_rq, se, sched_feat(ATTACH_AGE_LOAD) ? 0 : SKIP_AGE_LOAD);
        attach_entity_load_avg(cfs_rq, se, 0);
        update_tg_load_avg(cfs_rq, false);
        propagate_entity_cfs_rq(se);
}

static void detach_task_cfs_rq(struct task_struct *p)
{
        struct sched_entity *se = &p->se;
        struct cfs_rq *cfs_rq = cfs_rq_of(se);

        if (!vruntime_normalized(p)) {
                /*
                 * Fix up our vruntime so that the current sleep doesn't
                 * cause 'unlimited' sleep bonus.
                 */
                place_entity(cfs_rq, se, 0);
                se->vruntime -= cfs_rq->min_vruntime;
        }

        detach_entity_cfs_rq(se);
}

static void attach_task_cfs_rq(struct task_struct *p)
{
        struct sched_entity *se = &p->se;
        struct cfs_rq *cfs_rq = cfs_rq_of(se);

        attach_entity_cfs_rq(se);

        if (!vruntime_normalized(p))
                se->vruntime += cfs_rq->min_vruntime;
}

static void switched_from_fair(struct rq *rq, struct task_struct *p)
{
        detach_task_cfs_rq(p);
}

static void switched_to_fair(struct rq *rq, struct task_struct *p)
{
        attach_task_cfs_rq(p);

        if (task_on_rq_queued(p)) {
                /*
                 * We were most likely switched from sched_rt, so
                 * kick off the schedule if running, otherwise just see
                 * if we can still preempt the current task.
                 */
                if (rq->curr == p)
                        resched_curr(rq);
                else
                        check_preempt_curr(rq, p, 0);
        }
}

/* Account for a task changing its policy or group.
 *
 * This routine is mostly called to set cfs_rq->curr field when a task
 * migrates between groups/classes.
 */
static void set_curr_task_fair(struct rq *rq)
{
        struct sched_entity *se = &rq->curr->se;

        for_each_sched_entity(se) {
                struct cfs_rq *cfs_rq = cfs_rq_of(se);

                set_next_entity(cfs_rq, se);
                /* ensure bandwidth has been allocated on our new cfs_rq */
                account_cfs_rq_runtime(cfs_rq, 0);
        }
}

void init_cfs_rq(struct cfs_rq *cfs_rq)
{
        cfs_rq->tasks_timeline = RB_ROOT_CACHED;
        cfs_rq->min_vruntime = (u64)(-(1LL << 20));
#ifndef CONFIG_64BIT
        cfs_rq->min_vruntime_copy = cfs_rq->min_vruntime;
#endif
#ifdef CONFIG_SMP
        raw_spin_lock_init(&cfs_rq->removed.lock);
#endif
}

#ifdef CONFIG_FAIR_GROUP_SCHED
static void task_set_group_fair(struct task_struct *p)
{
        struct sched_entity *se = &p->se;

        set_task_rq(p, task_cpu(p));
        se->depth = se->parent ? se->parent->depth + 1 : 0;
}

static void task_move_group_fair(struct task_struct *p)
{
        detach_task_cfs_rq(p);
        set_task_rq(p, task_cpu(p));

#ifdef CONFIG_SMP
        /* Tell se's cfs_rq has been changed -- migrated */
        p->se.avg.last_update_time = 0;
#endif
        attach_task_cfs_rq(p);
}

static void task_change_group_fair(struct task_struct *p, int type)
{
        switch (type) {
        case TASK_SET_GROUP:
                task_set_group_fair(p);
                break;

        case TASK_MOVE_GROUP:
                task_move_group_fair(p);
                break;
        }
}

void free_fair_sched_group(struct task_group *tg)
{
        int i;

        destroy_cfs_bandwidth(tg_cfs_bandwidth(tg));

        for_each_possible_cpu(i) {
                if (tg->cfs_rq)
                        kfree(tg->cfs_rq[i]);
                if (tg->se)
                        kfree(tg->se[i]);
        }

        kfree(tg->cfs_rq);
        kfree(tg->se);
}

int alloc_fair_sched_group(struct task_group *tg, struct task_group *parent)
{
        struct sched_entity *se;
        struct cfs_rq *cfs_rq;
        int i;

        tg->cfs_rq = kcalloc(nr_cpu_ids, sizeof(cfs_rq), GFP_KERNEL);
        if (!tg->cfs_rq)
                goto err;
        tg->se = kcalloc(nr_cpu_ids, sizeof(se), GFP_KERNEL);
        if (!tg->se)
                goto err;

        tg->shares = NICE_0_LOAD;

        init_cfs_bandwidth(tg_cfs_bandwidth(tg));

        for_each_possible_cpu(i) {
                cfs_rq = kzalloc_node(sizeof(struct cfs_rq),
                                      GFP_KERNEL, cpu_to_node(i));
                if (!cfs_rq)
                        goto err;

                se = kzalloc_node(sizeof(struct sched_entity),
                                  GFP_KERNEL, cpu_to_node(i));
                if (!se)
                        goto err_free_rq;

                init_cfs_rq(cfs_rq);
                init_tg_cfs_entry(tg, cfs_rq, se, i, parent->se[i]);
                init_entity_runnable_average(se);
        }

        return 1;

err_free_rq:
        kfree(cfs_rq);
err:
        return 0;
}

void online_fair_sched_group(struct task_group *tg)
{
        struct sched_entity *se;
        struct rq *rq;
        int i;

        for_each_possible_cpu(i) {
                rq = cpu_rq(i);
                se = tg->se[i];

                raw_spin_lock_irq(&rq->lock);
                update_rq_clock(rq);
                attach_entity_cfs_rq(se);
                sync_throttle(tg, i);
                raw_spin_unlock_irq(&rq->lock);
        }
}

void unregister_fair_sched_group(struct task_group *tg)
{
        unsigned long flags;
        struct rq *rq;
        int cpu;

        for_each_possible_cpu(cpu) {
                if (tg->se[cpu])
                        remove_entity_load_avg(tg->se[cpu]);

                /*
                 * Only empty task groups can be destroyed; so we can speculatively
                 * check on_list without danger of it being re-added.
                 */
                if (!tg->cfs_rq[cpu]->on_list)
                        continue;

                rq = cpu_rq(cpu);

                raw_spin_lock_irqsave(&rq->lock, flags);
                list_del_leaf_cfs_rq(tg->cfs_rq[cpu]);
                raw_spin_unlock_irqrestore(&rq->lock, flags);
        }
}

void init_tg_cfs_entry(struct task_group *tg, struct cfs_rq *cfs_rq,
                        struct sched_entity *se, int cpu,
                        struct sched_entity *parent)
{
        struct rq *rq = cpu_rq(cpu);

        cfs_rq->tg = tg;
        cfs_rq->rq = rq;
        init_cfs_rq_runtime(cfs_rq);

        tg->cfs_rq[cpu] = cfs_rq;
        tg->se[cpu] = se;

        /* se could be NULL for root_task_group */
        if (!se)
                return;

        if (!parent) {
                se->cfs_rq = &rq->cfs;
                se->depth = 0;
        } else {
                se->cfs_rq = parent->my_q;
                se->depth = parent->depth + 1;
        }

        se->my_q = cfs_rq;
        /* guarantee group entities always have weight */
        update_load_set(&se->load, NICE_0_LOAD);
        se->parent = parent;
}

static DEFINE_MUTEX(shares_mutex);

int sched_group_set_shares(struct task_group *tg, unsigned long shares)
{
        int i;

        /*
         * We can't change the weight of the root cgroup.
         */
        if (!tg->se[0])
                return -EINVAL;

        shares = clamp(shares, scale_load(MIN_SHARES), scale_load(MAX_SHARES));

        mutex_lock(&shares_mutex);
        if (tg->shares == shares)
                goto done;

        tg->shares = shares;
        for_each_possible_cpu(i) {
                struct rq *rq = cpu_rq(i);
                struct sched_entity *se = tg->se[i];
                struct rq_flags rf;

                /* Propagate contribution to hierarchy */
                rq_lock_irqsave(rq, &rf);
                update_rq_clock(rq);
                for_each_sched_entity(se) {
                        update_load_avg(cfs_rq_of(se), se, UPDATE_TG);
                        update_cfs_group(se);
                }
                rq_unlock_irqrestore(rq, &rf);
        }

done:
        mutex_unlock(&shares_mutex);
        return 0;
}
#else /* CONFIG_FAIR_GROUP_SCHED */

void free_fair_sched_group(struct task_group *tg) { }

int alloc_fair_sched_group(struct task_group *tg, struct task_group *parent)
{
        return 1;
}

void online_fair_sched_group(struct task_group *tg) { }

void unregister_fair_sched_group(struct task_group *tg) { }

#endif /* CONFIG_FAIR_GROUP_SCHED */


static unsigned int get_rr_interval_fair(struct rq *rq, struct task_struct *task)
{
        struct sched_entity *se = &task->se;
        unsigned int rr_interval = 0;

        /*
         * Time slice is 0 for SCHED_OTHER tasks that are on an otherwise
         * idle runqueue:
         */
        if (rq->cfs.load.weight)
                rr_interval = NS_TO_JIFFIES(sched_slice(cfs_rq_of(se), se));

        return rr_interval;
}

/*
 * All the scheduling class methods:
 */
const struct sched_class fair_sched_class = {
        .next                   = &idle_sched_class,
        .enqueue_task           = enqueue_task_fair,
        .dequeue_task           = dequeue_task_fair,
        .yield_task             = yield_task_fair,
        .yield_to_task          = yield_to_task_fair,

        .check_preempt_curr     = check_preempt_wakeup,

        .pick_next_task         = pick_next_task_fair,
        .put_prev_task          = put_prev_task_fair,

#ifdef CONFIG_SMP
        .select_task_rq         = select_task_rq_fair,
        .migrate_task_rq        = migrate_task_rq_fair,

        .rq_online              = rq_online_fair,
        .rq_offline             = rq_offline_fair,

        .task_dead              = task_dead_fair,
        .set_cpus_allowed       = set_cpus_allowed_common,
#endif

        .set_curr_task          = set_curr_task_fair,
        .task_tick              = task_tick_fair,
        .task_fork              = task_fork_fair,

        .prio_changed           = prio_changed_fair,
        .switched_from          = switched_from_fair,
        .switched_to            = switched_to_fair,

        .get_rr_interval        = get_rr_interval_fair,

        .update_curr            = update_curr_fair,

#ifdef CONFIG_FAIR_GROUP_SCHED
        .task_change_group      = task_change_group_fair,
#endif
};

#ifdef CONFIG_SCHED_DEBUG
void print_cfs_stats(struct seq_file *m, int cpu)
{
        struct cfs_rq *cfs_rq, *pos;

        rcu_read_lock();
        for_each_leaf_cfs_rq_safe(cpu_rq(cpu), cfs_rq, pos)
                print_cfs_rq(m, cpu, cfs_rq);
        rcu_read_unlock();
}

#ifdef CONFIG_NUMA_BALANCING
void show_numa_stats(struct task_struct *p, struct seq_file *m)
{
        int node;
        unsigned long tsf = 0, tpf = 0, gsf = 0, gpf = 0;

        for_each_online_node(node) {
                if (p->numa_faults) {
                        tsf = p->numa_faults[task_faults_idx(NUMA_MEM, node, 0)];
                        tpf = p->numa_faults[task_faults_idx(NUMA_MEM, node, 1)];
                }
                if (p->numa_group) {
                        gsf = p->numa_group->faults[task_faults_idx(NUMA_MEM, node, 0)],
                        gpf = p->numa_group->faults[task_faults_idx(NUMA_MEM, node, 1)];
                }
                print_numa_stats(m, node, tsf, tpf, gsf, gpf);
        }
}
#endif /* CONFIG_NUMA_BALANCING */
#endif /* CONFIG_SCHED_DEBUG */

__init void init_sched_fair_class(void)
{
#ifdef CONFIG_SMP
        open_softirq(SCHED_SOFTIRQ, run_rebalance_domains);

#ifdef CONFIG_NO_HZ_COMMON
        nohz.next_balance = jiffies;
        nohz.next_blocked = jiffies;
        zalloc_cpumask_var(&nohz.idle_cpus_mask, GFP_NOWAIT);
#endif
#endif /* SMP */

}