Merge tag 'nfs-for-5.15-1' of git://git.linux-nfs.org/projects/anna/linux-nfs

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

// SPDX-License-Identifier: GPL-2.0
/*
 * Real-Time Scheduling Class (mapped to the SCHED_FIFO and SCHED_RR
 * policies)
 */
#include "sched.h"

#include "pelt.h"

int sched_rr_timeslice = RR_TIMESLICE;
int sysctl_sched_rr_timeslice = (MSEC_PER_SEC / HZ) * RR_TIMESLICE;
/* More than 4 hours if BW_SHIFT equals 20. */
static const u64 max_rt_runtime = MAX_BW;

static int do_sched_rt_period_timer(struct rt_bandwidth *rt_b, int overrun);

struct rt_bandwidth def_rt_bandwidth;

static enum hrtimer_restart sched_rt_period_timer(struct hrtimer *timer)
{
        struct rt_bandwidth *rt_b =
                container_of(timer, struct rt_bandwidth, rt_period_timer);
        int idle = 0;
        int overrun;

        raw_spin_lock(&rt_b->rt_runtime_lock);
        for (;;) {
                overrun = hrtimer_forward_now(timer, rt_b->rt_period);
                if (!overrun)
                        break;

                raw_spin_unlock(&rt_b->rt_runtime_lock);
                idle = do_sched_rt_period_timer(rt_b, overrun);
                raw_spin_lock(&rt_b->rt_runtime_lock);
        }
        if (idle)
                rt_b->rt_period_active = 0;
        raw_spin_unlock(&rt_b->rt_runtime_lock);

        return idle ? HRTIMER_NORESTART : HRTIMER_RESTART;
}

void init_rt_bandwidth(struct rt_bandwidth *rt_b, u64 period, u64 runtime)
{
        rt_b->rt_period = ns_to_ktime(period);
        rt_b->rt_runtime = runtime;

        raw_spin_lock_init(&rt_b->rt_runtime_lock);

        hrtimer_init(&rt_b->rt_period_timer, CLOCK_MONOTONIC,
                     HRTIMER_MODE_REL_HARD);
        rt_b->rt_period_timer.function = sched_rt_period_timer;
}

static void start_rt_bandwidth(struct rt_bandwidth *rt_b)
{
        if (!rt_bandwidth_enabled() || rt_b->rt_runtime == RUNTIME_INF)
                return;

        raw_spin_lock(&rt_b->rt_runtime_lock);
        if (!rt_b->rt_period_active) {
                rt_b->rt_period_active = 1;
                /*
                 * SCHED_DEADLINE updates the bandwidth, as a run away
                 * RT task with a DL task could hog a CPU. But DL does
                 * not reset the period. If a deadline task was running
                 * without an RT task running, it can cause RT tasks to
                 * throttle when they start up. Kick the timer right away
                 * to update the period.
                 */
                hrtimer_forward_now(&rt_b->rt_period_timer, ns_to_ktime(0));
                hrtimer_start_expires(&rt_b->rt_period_timer,
                                      HRTIMER_MODE_ABS_PINNED_HARD);
        }
        raw_spin_unlock(&rt_b->rt_runtime_lock);
}

void init_rt_rq(struct rt_rq *rt_rq)
{
        struct rt_prio_array *array;
        int i;

        array = &rt_rq->active;
        for (i = 0; i < MAX_RT_PRIO; i++) {
                INIT_LIST_HEAD(array->queue + i);
                __clear_bit(i, array->bitmap);
        }
        /* delimiter for bitsearch: */
        __set_bit(MAX_RT_PRIO, array->bitmap);

#if defined CONFIG_SMP
        rt_rq->highest_prio.curr = MAX_RT_PRIO-1;
        rt_rq->highest_prio.next = MAX_RT_PRIO-1;
        rt_rq->rt_nr_migratory = 0;
        rt_rq->overloaded = 0;
        plist_head_init(&rt_rq->pushable_tasks);
#endif /* CONFIG_SMP */
        /* We start is dequeued state, because no RT tasks are queued */
        rt_rq->rt_queued = 0;

        rt_rq->rt_time = 0;
        rt_rq->rt_throttled = 0;
        rt_rq->rt_runtime = 0;
        raw_spin_lock_init(&rt_rq->rt_runtime_lock);
}

#ifdef CONFIG_RT_GROUP_SCHED
static void destroy_rt_bandwidth(struct rt_bandwidth *rt_b)
{
        hrtimer_cancel(&rt_b->rt_period_timer);
}

#define rt_entity_is_task(rt_se) (!(rt_se)->my_q)

static inline struct task_struct *rt_task_of(struct sched_rt_entity *rt_se)
{
#ifdef CONFIG_SCHED_DEBUG
        WARN_ON_ONCE(!rt_entity_is_task(rt_se));
#endif
        return container_of(rt_se, struct task_struct, rt);
}

static inline struct rq *rq_of_rt_rq(struct rt_rq *rt_rq)
{
        return rt_rq->rq;
}

static inline struct rt_rq *rt_rq_of_se(struct sched_rt_entity *rt_se)
{
        return rt_se->rt_rq;
}

static inline struct rq *rq_of_rt_se(struct sched_rt_entity *rt_se)
{
        struct rt_rq *rt_rq = rt_se->rt_rq;

        return rt_rq->rq;
}

void free_rt_sched_group(struct task_group *tg)
{
        int i;

        if (tg->rt_se)
                destroy_rt_bandwidth(&tg->rt_bandwidth);

        for_each_possible_cpu(i) {
                if (tg->rt_rq)
                        kfree(tg->rt_rq[i]);
                if (tg->rt_se)
                        kfree(tg->rt_se[i]);
        }

        kfree(tg->rt_rq);
        kfree(tg->rt_se);
}

void init_tg_rt_entry(struct task_group *tg, struct rt_rq *rt_rq,
                struct sched_rt_entity *rt_se, int cpu,
                struct sched_rt_entity *parent)
{
        struct rq *rq = cpu_rq(cpu);

        rt_rq->highest_prio.curr = MAX_RT_PRIO-1;
        rt_rq->rt_nr_boosted = 0;
        rt_rq->rq = rq;
        rt_rq->tg = tg;

        tg->rt_rq[cpu] = rt_rq;
        tg->rt_se[cpu] = rt_se;

        if (!rt_se)
                return;

        if (!parent)
                rt_se->rt_rq = &rq->rt;
        else
                rt_se->rt_rq = parent->my_q;

        rt_se->my_q = rt_rq;
        rt_se->parent = parent;
        INIT_LIST_HEAD(&rt_se->run_list);
}

int alloc_rt_sched_group(struct task_group *tg, struct task_group *parent)
{
        struct rt_rq *rt_rq;
        struct sched_rt_entity *rt_se;
        int i;

        tg->rt_rq = kcalloc(nr_cpu_ids, sizeof(rt_rq), GFP_KERNEL);
        if (!tg->rt_rq)
                goto err;
        tg->rt_se = kcalloc(nr_cpu_ids, sizeof(rt_se), GFP_KERNEL);
        if (!tg->rt_se)
                goto err;

        init_rt_bandwidth(&tg->rt_bandwidth,
                        ktime_to_ns(def_rt_bandwidth.rt_period), 0);

        for_each_possible_cpu(i) {
                rt_rq = kzalloc_node(sizeof(struct rt_rq),
                                     GFP_KERNEL, cpu_to_node(i));
                if (!rt_rq)
                        goto err;

                rt_se = kzalloc_node(sizeof(struct sched_rt_entity),
                                     GFP_KERNEL, cpu_to_node(i));
                if (!rt_se)
                        goto err_free_rq;

                init_rt_rq(rt_rq);
                rt_rq->rt_runtime = tg->rt_bandwidth.rt_runtime;
                init_tg_rt_entry(tg, rt_rq, rt_se, i, parent->rt_se[i]);
        }

        return 1;

err_free_rq:
        kfree(rt_rq);
err:
        return 0;
}

#else /* CONFIG_RT_GROUP_SCHED */

#define rt_entity_is_task(rt_se) (1)

static inline struct task_struct *rt_task_of(struct sched_rt_entity *rt_se)
{
        return container_of(rt_se, struct task_struct, rt);
}

static inline struct rq *rq_of_rt_rq(struct rt_rq *rt_rq)
{
        return container_of(rt_rq, struct rq, rt);
}

static inline struct rq *rq_of_rt_se(struct sched_rt_entity *rt_se)
{
        struct task_struct *p = rt_task_of(rt_se);

        return task_rq(p);
}

static inline struct rt_rq *rt_rq_of_se(struct sched_rt_entity *rt_se)
{
        struct rq *rq = rq_of_rt_se(rt_se);

        return &rq->rt;
}

void free_rt_sched_group(struct task_group *tg) { }

int alloc_rt_sched_group(struct task_group *tg, struct task_group *parent)
{
        return 1;
}
#endif /* CONFIG_RT_GROUP_SCHED */

#ifdef CONFIG_SMP

static void pull_rt_task(struct rq *this_rq);

static inline bool need_pull_rt_task(struct rq *rq, struct task_struct *prev)
{
        /* Try to pull RT tasks here if we lower this rq's prio */
        return rq->online && rq->rt.highest_prio.curr > prev->prio;
}

static inline int rt_overloaded(struct rq *rq)
{
        return atomic_read(&rq->rd->rto_count);
}

static inline void rt_set_overload(struct rq *rq)
{
        if (!rq->online)
                return;

        cpumask_set_cpu(rq->cpu, rq->rd->rto_mask);
        /*
         * Make sure the mask is visible before we set
         * the overload count. That is checked to determine
         * if we should look at the mask. It would be a shame
         * if we looked at the mask, but the mask was not
         * updated yet.
         *
         * Matched by the barrier in pull_rt_task().
         */
        smp_wmb();
        atomic_inc(&rq->rd->rto_count);
}

static inline void rt_clear_overload(struct rq *rq)
{
        if (!rq->online)
                return;

        /* the order here really doesn't matter */
        atomic_dec(&rq->rd->rto_count);
        cpumask_clear_cpu(rq->cpu, rq->rd->rto_mask);
}

static void update_rt_migration(struct rt_rq *rt_rq)
{
        if (rt_rq->rt_nr_migratory && rt_rq->rt_nr_total > 1) {
                if (!rt_rq->overloaded) {
                        rt_set_overload(rq_of_rt_rq(rt_rq));
                        rt_rq->overloaded = 1;
                }
        } else if (rt_rq->overloaded) {
                rt_clear_overload(rq_of_rt_rq(rt_rq));
                rt_rq->overloaded = 0;
        }
}

static void inc_rt_migration(struct sched_rt_entity *rt_se, struct rt_rq *rt_rq)
{
        struct task_struct *p;

        if (!rt_entity_is_task(rt_se))
                return;

        p = rt_task_of(rt_se);
        rt_rq = &rq_of_rt_rq(rt_rq)->rt;

        rt_rq->rt_nr_total++;
        if (p->nr_cpus_allowed > 1)
                rt_rq->rt_nr_migratory++;

        update_rt_migration(rt_rq);
}

static void dec_rt_migration(struct sched_rt_entity *rt_se, struct rt_rq *rt_rq)
{
        struct task_struct *p;

        if (!rt_entity_is_task(rt_se))
                return;

        p = rt_task_of(rt_se);
        rt_rq = &rq_of_rt_rq(rt_rq)->rt;

        rt_rq->rt_nr_total--;
        if (p->nr_cpus_allowed > 1)
                rt_rq->rt_nr_migratory--;

        update_rt_migration(rt_rq);
}

static inline int has_pushable_tasks(struct rq *rq)
{
        return !plist_head_empty(&rq->rt.pushable_tasks);
}

static DEFINE_PER_CPU(struct callback_head, rt_push_head);
static DEFINE_PER_CPU(struct callback_head, rt_pull_head);

static void push_rt_tasks(struct rq *);
static void pull_rt_task(struct rq *);

static inline void rt_queue_push_tasks(struct rq *rq)
{
        if (!has_pushable_tasks(rq))
                return;

        queue_balance_callback(rq, &per_cpu(rt_push_head, rq->cpu), push_rt_tasks);
}

static inline void rt_queue_pull_task(struct rq *rq)
{
        queue_balance_callback(rq, &per_cpu(rt_pull_head, rq->cpu), pull_rt_task);
}

static void enqueue_pushable_task(struct rq *rq, struct task_struct *p)
{
        plist_del(&p->pushable_tasks, &rq->rt.pushable_tasks);
        plist_node_init(&p->pushable_tasks, p->prio);
        plist_add(&p->pushable_tasks, &rq->rt.pushable_tasks);

        /* Update the highest prio pushable task */
        if (p->prio < rq->rt.highest_prio.next)
                rq->rt.highest_prio.next = p->prio;
}

static void dequeue_pushable_task(struct rq *rq, struct task_struct *p)
{
        plist_del(&p->pushable_tasks, &rq->rt.pushable_tasks);

        /* Update the new highest prio pushable task */
        if (has_pushable_tasks(rq)) {
                p = plist_first_entry(&rq->rt.pushable_tasks,
                                      struct task_struct, pushable_tasks);
                rq->rt.highest_prio.next = p->prio;
        } else {
                rq->rt.highest_prio.next = MAX_RT_PRIO-1;
        }
}

#else

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

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

static inline
void inc_rt_migration(struct sched_rt_entity *rt_se, struct rt_rq *rt_rq)
{
}

static inline
void dec_rt_migration(struct sched_rt_entity *rt_se, struct rt_rq *rt_rq)
{
}

static inline bool need_pull_rt_task(struct rq *rq, struct task_struct *prev)
{
        return false;
}

static inline void pull_rt_task(struct rq *this_rq)
{
}

static inline void rt_queue_push_tasks(struct rq *rq)
{
}
#endif /* CONFIG_SMP */

static void enqueue_top_rt_rq(struct rt_rq *rt_rq);
static void dequeue_top_rt_rq(struct rt_rq *rt_rq);

static inline int on_rt_rq(struct sched_rt_entity *rt_se)
{
        return rt_se->on_rq;
}

#ifdef CONFIG_UCLAMP_TASK
/*
 * Verify the fitness of task @p to run on @cpu taking into account the uclamp
 * settings.
 *
 * This check is only important for heterogeneous systems where uclamp_min value
 * is higher than the capacity of a @cpu. For non-heterogeneous system this
 * function will always return true.
 *
 * The function will return true if the capacity of the @cpu is >= the
 * uclamp_min and false otherwise.
 *
 * Note that uclamp_min will be clamped to uclamp_max if uclamp_min
 * > uclamp_max.
 */
static inline bool rt_task_fits_capacity(struct task_struct *p, int cpu)
{
        unsigned int min_cap;
        unsigned int max_cap;
        unsigned int cpu_cap;

        /* Only heterogeneous systems can benefit from this check */
        if (!static_branch_unlikely(&sched_asym_cpucapacity))
                return true;

        min_cap = uclamp_eff_value(p, UCLAMP_MIN);
        max_cap = uclamp_eff_value(p, UCLAMP_MAX);

        cpu_cap = capacity_orig_of(cpu);

        return cpu_cap >= min(min_cap, max_cap);
}
#else
static inline bool rt_task_fits_capacity(struct task_struct *p, int cpu)
{
        return true;
}
#endif

#ifdef CONFIG_RT_GROUP_SCHED

static inline u64 sched_rt_runtime(struct rt_rq *rt_rq)
{
        if (!rt_rq->tg)
                return RUNTIME_INF;

        return rt_rq->rt_runtime;
}

static inline u64 sched_rt_period(struct rt_rq *rt_rq)
{
        return ktime_to_ns(rt_rq->tg->rt_bandwidth.rt_period);
}

typedef struct task_group *rt_rq_iter_t;

static inline struct task_group *next_task_group(struct task_group *tg)
{
        do {
                tg = list_entry_rcu(tg->list.next,
                        typeof(struct task_group), list);
        } while (&tg->list != &task_groups && task_group_is_autogroup(tg));

        if (&tg->list == &task_groups)
                tg = NULL;

        return tg;
}

#define for_each_rt_rq(rt_rq, iter, rq)                                 \
        for (iter = container_of(&task_groups, typeof(*iter), list);    \
                (iter = next_task_group(iter)) &&                       \
                (rt_rq = iter->rt_rq[cpu_of(rq)]);)

#define for_each_sched_rt_entity(rt_se) \
        for (; rt_se; rt_se = rt_se->parent)

static inline struct rt_rq *group_rt_rq(struct sched_rt_entity *rt_se)
{
        return rt_se->my_q;
}

static void enqueue_rt_entity(struct sched_rt_entity *rt_se, unsigned int flags);
static void dequeue_rt_entity(struct sched_rt_entity *rt_se, unsigned int flags);

static void sched_rt_rq_enqueue(struct rt_rq *rt_rq)
{
        struct task_struct *curr = rq_of_rt_rq(rt_rq)->curr;
        struct rq *rq = rq_of_rt_rq(rt_rq);
        struct sched_rt_entity *rt_se;

        int cpu = cpu_of(rq);

        rt_se = rt_rq->tg->rt_se[cpu];

        if (rt_rq->rt_nr_running) {
                if (!rt_se)
                        enqueue_top_rt_rq(rt_rq);
                else if (!on_rt_rq(rt_se))
                        enqueue_rt_entity(rt_se, 0);

                if (rt_rq->highest_prio.curr < curr->prio)
                        resched_curr(rq);
        }
}

static void sched_rt_rq_dequeue(struct rt_rq *rt_rq)
{
        struct sched_rt_entity *rt_se;
        int cpu = cpu_of(rq_of_rt_rq(rt_rq));

        rt_se = rt_rq->tg->rt_se[cpu];

        if (!rt_se) {
                dequeue_top_rt_rq(rt_rq);
                /* Kick cpufreq (see the comment in kernel/sched/sched.h). */
                cpufreq_update_util(rq_of_rt_rq(rt_rq), 0);
        }
        else if (on_rt_rq(rt_se))
                dequeue_rt_entity(rt_se, 0);
}

static inline int rt_rq_throttled(struct rt_rq *rt_rq)
{
        return rt_rq->rt_throttled && !rt_rq->rt_nr_boosted;
}

static int rt_se_boosted(struct sched_rt_entity *rt_se)
{
        struct rt_rq *rt_rq = group_rt_rq(rt_se);
        struct task_struct *p;

        if (rt_rq)
                return !!rt_rq->rt_nr_boosted;

        p = rt_task_of(rt_se);
        return p->prio != p->normal_prio;
}

#ifdef CONFIG_SMP
static inline const struct cpumask *sched_rt_period_mask(void)
{
        return this_rq()->rd->span;
}
#else
static inline const struct cpumask *sched_rt_period_mask(void)
{
        return cpu_online_mask;
}
#endif

static inline
struct rt_rq *sched_rt_period_rt_rq(struct rt_bandwidth *rt_b, int cpu)
{
        return container_of(rt_b, struct task_group, rt_bandwidth)->rt_rq[cpu];
}

static inline struct rt_bandwidth *sched_rt_bandwidth(struct rt_rq *rt_rq)
{
        return &rt_rq->tg->rt_bandwidth;
}

#else /* !CONFIG_RT_GROUP_SCHED */

static inline u64 sched_rt_runtime(struct rt_rq *rt_rq)
{
        return rt_rq->rt_runtime;
}

static inline u64 sched_rt_period(struct rt_rq *rt_rq)
{
        return ktime_to_ns(def_rt_bandwidth.rt_period);
}

typedef struct rt_rq *rt_rq_iter_t;

#define for_each_rt_rq(rt_rq, iter, rq) \
        for ((void) iter, rt_rq = &rq->rt; rt_rq; rt_rq = NULL)

#define for_each_sched_rt_entity(rt_se) \
        for (; rt_se; rt_se = NULL)

static inline struct rt_rq *group_rt_rq(struct sched_rt_entity *rt_se)
{
        return NULL;
}

static inline void sched_rt_rq_enqueue(struct rt_rq *rt_rq)
{
        struct rq *rq = rq_of_rt_rq(rt_rq);

        if (!rt_rq->rt_nr_running)
                return;

        enqueue_top_rt_rq(rt_rq);
        resched_curr(rq);
}

static inline void sched_rt_rq_dequeue(struct rt_rq *rt_rq)
{
        dequeue_top_rt_rq(rt_rq);
}

static inline int rt_rq_throttled(struct rt_rq *rt_rq)
{
        return rt_rq->rt_throttled;
}

static inline const struct cpumask *sched_rt_period_mask(void)
{
        return cpu_online_mask;
}

static inline
struct rt_rq *sched_rt_period_rt_rq(struct rt_bandwidth *rt_b, int cpu)
{
        return &cpu_rq(cpu)->rt;
}

static inline struct rt_bandwidth *sched_rt_bandwidth(struct rt_rq *rt_rq)
{
        return &def_rt_bandwidth;
}

#endif /* CONFIG_RT_GROUP_SCHED */

bool sched_rt_bandwidth_account(struct rt_rq *rt_rq)
{
        struct rt_bandwidth *rt_b = sched_rt_bandwidth(rt_rq);

        return (hrtimer_active(&rt_b->rt_period_timer) ||
                rt_rq->rt_time < rt_b->rt_runtime);
}

#ifdef CONFIG_SMP
/*
 * We ran out of runtime, see if we can borrow some from our neighbours.
 */
static void do_balance_runtime(struct rt_rq *rt_rq)
{
        struct rt_bandwidth *rt_b = sched_rt_bandwidth(rt_rq);
        struct root_domain *rd = rq_of_rt_rq(rt_rq)->rd;
        int i, weight;
        u64 rt_period;

        weight = cpumask_weight(rd->span);

        raw_spin_lock(&rt_b->rt_runtime_lock);
        rt_period = ktime_to_ns(rt_b->rt_period);
        for_each_cpu(i, rd->span) {
                struct rt_rq *iter = sched_rt_period_rt_rq(rt_b, i);
                s64 diff;

                if (iter == rt_rq)
                        continue;

                raw_spin_lock(&iter->rt_runtime_lock);
                /*
                 * Either all rqs have inf runtime and there's nothing to steal
                 * or __disable_runtime() below sets a specific rq to inf to
                 * indicate its been disabled and disallow stealing.
                 */
                if (iter->rt_runtime == RUNTIME_INF)
                        goto next;

                /*
                 * From runqueues with spare time, take 1/n part of their
                 * spare time, but no more than our period.
                 */
                diff = iter->rt_runtime - iter->rt_time;
                if (diff > 0) {
                        diff = div_u64((u64)diff, weight);
                        if (rt_rq->rt_runtime + diff > rt_period)
                                diff = rt_period - rt_rq->rt_runtime;
                        iter->rt_runtime -= diff;
                        rt_rq->rt_runtime += diff;
                        if (rt_rq->rt_runtime == rt_period) {
                                raw_spin_unlock(&iter->rt_runtime_lock);
                                break;
                        }
                }
next:
                raw_spin_unlock(&iter->rt_runtime_lock);
        }
        raw_spin_unlock(&rt_b->rt_runtime_lock);
}

/*
 * Ensure this RQ takes back all the runtime it lend to its neighbours.
 */
static void __disable_runtime(struct rq *rq)
{
        struct root_domain *rd = rq->rd;
        rt_rq_iter_t iter;
        struct rt_rq *rt_rq;

        if (unlikely(!scheduler_running))
                return;

        for_each_rt_rq(rt_rq, iter, rq) {
                struct rt_bandwidth *rt_b = sched_rt_bandwidth(rt_rq);
                s64 want;
                int i;

                raw_spin_lock(&rt_b->rt_runtime_lock);
                raw_spin_lock(&rt_rq->rt_runtime_lock);
                /*
                 * Either we're all inf and nobody needs to borrow, or we're
                 * already disabled and thus have nothing to do, or we have
                 * exactly the right amount of runtime to take out.
                 */
                if (rt_rq->rt_runtime == RUNTIME_INF ||
                                rt_rq->rt_runtime == rt_b->rt_runtime)
                        goto balanced;
                raw_spin_unlock(&rt_rq->rt_runtime_lock);

                /*
                 * Calculate the difference between what we started out with
                 * and what we current have, that's the amount of runtime
                 * we lend and now have to reclaim.
                 */
                want = rt_b->rt_runtime - rt_rq->rt_runtime;

                /*
                 * Greedy reclaim, take back as much as we can.
                 */
                for_each_cpu(i, rd->span) {
                        struct rt_rq *iter = sched_rt_period_rt_rq(rt_b, i);
                        s64 diff;

                        /*
                         * Can't reclaim from ourselves or disabled runqueues.
                         */
                        if (iter == rt_rq || iter->rt_runtime == RUNTIME_INF)
                                continue;

                        raw_spin_lock(&iter->rt_runtime_lock);
                        if (want > 0) {
                                diff = min_t(s64, iter->rt_runtime, want);
                                iter->rt_runtime -= diff;
                                want -= diff;
                        } else {
                                iter->rt_runtime -= want;
                                want -= want;
                        }
                        raw_spin_unlock(&iter->rt_runtime_lock);

                        if (!want)
                                break;
                }

                raw_spin_lock(&rt_rq->rt_runtime_lock);
                /*
                 * We cannot be left wanting - that would mean some runtime
                 * leaked out of the system.
                 */
                BUG_ON(want);
balanced:
                /*
                 * Disable all the borrow logic by pretending we have inf
                 * runtime - in which case borrowing doesn't make sense.
                 */
                rt_rq->rt_runtime = RUNTIME_INF;
                rt_rq->rt_throttled = 0;
                raw_spin_unlock(&rt_rq->rt_runtime_lock);
                raw_spin_unlock(&rt_b->rt_runtime_lock);

                /* Make rt_rq available for pick_next_task() */
                sched_rt_rq_enqueue(rt_rq);
        }
}

static void __enable_runtime(struct rq *rq)
{
        rt_rq_iter_t iter;
        struct rt_rq *rt_rq;

        if (unlikely(!scheduler_running))
                return;

        /*
         * Reset each runqueue's bandwidth settings
         */
        for_each_rt_rq(rt_rq, iter, rq) {
                struct rt_bandwidth *rt_b = sched_rt_bandwidth(rt_rq);

                raw_spin_lock(&rt_b->rt_runtime_lock);
                raw_spin_lock(&rt_rq->rt_runtime_lock);
                rt_rq->rt_runtime = rt_b->rt_runtime;
                rt_rq->rt_time = 0;
                rt_rq->rt_throttled = 0;
                raw_spin_unlock(&rt_rq->rt_runtime_lock);
                raw_spin_unlock(&rt_b->rt_runtime_lock);
        }
}

static void balance_runtime(struct rt_rq *rt_rq)
{
        if (!sched_feat(RT_RUNTIME_SHARE))
                return;

        if (rt_rq->rt_time > rt_rq->rt_runtime) {
                raw_spin_unlock(&rt_rq->rt_runtime_lock);
                do_balance_runtime(rt_rq);
                raw_spin_lock(&rt_rq->rt_runtime_lock);
        }
}
#else /* !CONFIG_SMP */
static inline void balance_runtime(struct rt_rq *rt_rq) {}
#endif /* CONFIG_SMP */

static int do_sched_rt_period_timer(struct rt_bandwidth *rt_b, int overrun)
{
        int i, idle = 1, throttled = 0;
        const struct cpumask *span;

        span = sched_rt_period_mask();
#ifdef CONFIG_RT_GROUP_SCHED
        /*
         * FIXME: isolated CPUs should really leave the root task group,
         * whether they are isolcpus or were isolated via cpusets, lest
         * the timer run on a CPU which does not service all runqueues,
         * potentially leaving other CPUs indefinitely throttled.  If
         * isolation is really required, the user will turn the throttle
         * off to kill the perturbations it causes anyway.  Meanwhile,
         * this maintains functionality for boot and/or troubleshooting.
         */
        if (rt_b == &root_task_group.rt_bandwidth)
                span = cpu_online_mask;
#endif
        for_each_cpu(i, span) {
                int enqueue = 0;
                struct rt_rq *rt_rq = sched_rt_period_rt_rq(rt_b, i);
                struct rq *rq = rq_of_rt_rq(rt_rq);
                int skip;

                /*
                 * When span == cpu_online_mask, taking each rq->lock
                 * can be time-consuming. Try to avoid it when possible.
                 */
                raw_spin_lock(&rt_rq->rt_runtime_lock);
                if (!sched_feat(RT_RUNTIME_SHARE) && rt_rq->rt_runtime != RUNTIME_INF)
                        rt_rq->rt_runtime = rt_b->rt_runtime;
                skip = !rt_rq->rt_time && !rt_rq->rt_nr_running;
                raw_spin_unlock(&rt_rq->rt_runtime_lock);
                if (skip)
                        continue;

                raw_spin_rq_lock(rq);
                update_rq_clock(rq);

                if (rt_rq->rt_time) {
                        u64 runtime;

                        raw_spin_lock(&rt_rq->rt_runtime_lock);
                        if (rt_rq->rt_throttled)
                                balance_runtime(rt_rq);
                        runtime = rt_rq->rt_runtime;
                        rt_rq->rt_time -= min(rt_rq->rt_time, overrun*runtime);
                        if (rt_rq->rt_throttled && rt_rq->rt_time < runtime) {
                                rt_rq->rt_throttled = 0;
                                enqueue = 1;

                                /*
                                 * When we're idle and a woken (rt) task is
                                 * throttled check_preempt_curr() will set
                                 * skip_update and the time between the wakeup
                                 * and this unthrottle will get accounted as
                                 * 'runtime'.
                                 */
                                if (rt_rq->rt_nr_running && rq->curr == rq->idle)
                                        rq_clock_cancel_skipupdate(rq);
                        }
                        if (rt_rq->rt_time || rt_rq->rt_nr_running)
                                idle = 0;
                        raw_spin_unlock(&rt_rq->rt_runtime_lock);
                } else if (rt_rq->rt_nr_running) {
                        idle = 0;
                        if (!rt_rq_throttled(rt_rq))
                                enqueue = 1;
                }
                if (rt_rq->rt_throttled)
                        throttled = 1;

                if (enqueue)
                        sched_rt_rq_enqueue(rt_rq);
                raw_spin_rq_unlock(rq);
        }

        if (!throttled && (!rt_bandwidth_enabled() || rt_b->rt_runtime == RUNTIME_INF))
                return 1;

        return idle;
}

static inline int rt_se_prio(struct sched_rt_entity *rt_se)
{
#ifdef CONFIG_RT_GROUP_SCHED
        struct rt_rq *rt_rq = group_rt_rq(rt_se);

        if (rt_rq)
                return rt_rq->highest_prio.curr;
#endif

        return rt_task_of(rt_se)->prio;
}

static int sched_rt_runtime_exceeded(struct rt_rq *rt_rq)
{
        u64 runtime = sched_rt_runtime(rt_rq);

        if (rt_rq->rt_throttled)
                return rt_rq_throttled(rt_rq);

        if (runtime >= sched_rt_period(rt_rq))
                return 0;

        balance_runtime(rt_rq);
        runtime = sched_rt_runtime(rt_rq);
        if (runtime == RUNTIME_INF)
                return 0;

        if (rt_rq->rt_time > runtime) {
                struct rt_bandwidth *rt_b = sched_rt_bandwidth(rt_rq);

                /*
                 * Don't actually throttle groups that have no runtime assigned
                 * but accrue some time due to boosting.
                 */
                if (likely(rt_b->rt_runtime)) {
                        rt_rq->rt_throttled = 1;
                        printk_deferred_once("sched: RT throttling activated\n");
                } else {
                        /*
                         * In case we did anyway, make it go away,
                         * replenishment is a joke, since it will replenish us
                         * with exactly 0 ns.
                         */
                        rt_rq->rt_time = 0;
                }

                if (rt_rq_throttled(rt_rq)) {
                        sched_rt_rq_dequeue(rt_rq);
                        return 1;
                }
        }

        return 0;
}

/*
 * Update the current task's runtime statistics. Skip current tasks that
 * are not in our scheduling class.
 */
static void update_curr_rt(struct rq *rq)
{
        struct task_struct *curr = rq->curr;
        struct sched_rt_entity *rt_se = &curr->rt;
        u64 delta_exec;
        u64 now;

        if (curr->sched_class != &rt_sched_class)
                return;

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

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

        curr->se.sum_exec_runtime += delta_exec;
        account_group_exec_runtime(curr, delta_exec);

        curr->se.exec_start = now;
        cgroup_account_cputime(curr, delta_exec);

        if (!rt_bandwidth_enabled())
                return;

        for_each_sched_rt_entity(rt_se) {
                struct rt_rq *rt_rq = rt_rq_of_se(rt_se);

                if (sched_rt_runtime(rt_rq) != RUNTIME_INF) {
                        raw_spin_lock(&rt_rq->rt_runtime_lock);
                        rt_rq->rt_time += delta_exec;
                        if (sched_rt_runtime_exceeded(rt_rq))
                                resched_curr(rq);
                        raw_spin_unlock(&rt_rq->rt_runtime_lock);
                }
        }
}

static void
dequeue_top_rt_rq(struct rt_rq *rt_rq)
{
        struct rq *rq = rq_of_rt_rq(rt_rq);

        BUG_ON(&rq->rt != rt_rq);

        if (!rt_rq->rt_queued)
                return;

        BUG_ON(!rq->nr_running);

        sub_nr_running(rq, rt_rq->rt_nr_running);
        rt_rq->rt_queued = 0;

}

static void
enqueue_top_rt_rq(struct rt_rq *rt_rq)
{
        struct rq *rq = rq_of_rt_rq(rt_rq);

        BUG_ON(&rq->rt != rt_rq);

        if (rt_rq->rt_queued)
                return;

        if (rt_rq_throttled(rt_rq))
                return;

        if (rt_rq->rt_nr_running) {
                add_nr_running(rq, rt_rq->rt_nr_running);
                rt_rq->rt_queued = 1;
        }

        /* Kick cpufreq (see the comment in kernel/sched/sched.h). */
        cpufreq_update_util(rq, 0);
}

#if defined CONFIG_SMP

static void
inc_rt_prio_smp(struct rt_rq *rt_rq, int prio, int prev_prio)
{
        struct rq *rq = rq_of_rt_rq(rt_rq);

#ifdef CONFIG_RT_GROUP_SCHED
        /*
         * Change rq's cpupri only if rt_rq is the top queue.
         */
        if (&rq->rt != rt_rq)
                return;
#endif
        if (rq->online && prio < prev_prio)
                cpupri_set(&rq->rd->cpupri, rq->cpu, prio);
}

static void
dec_rt_prio_smp(struct rt_rq *rt_rq, int prio, int prev_prio)
{
        struct rq *rq = rq_of_rt_rq(rt_rq);

#ifdef CONFIG_RT_GROUP_SCHED
        /*
         * Change rq's cpupri only if rt_rq is the top queue.
         */
        if (&rq->rt != rt_rq)
                return;
#endif
        if (rq->online && rt_rq->highest_prio.curr != prev_prio)
                cpupri_set(&rq->rd->cpupri, rq->cpu, rt_rq->highest_prio.curr);
}

#else /* CONFIG_SMP */

static inline
void inc_rt_prio_smp(struct rt_rq *rt_rq, int prio, int prev_prio) {}
static inline
void dec_rt_prio_smp(struct rt_rq *rt_rq, int prio, int prev_prio) {}

#endif /* CONFIG_SMP */

#if defined CONFIG_SMP || defined CONFIG_RT_GROUP_SCHED
static void
inc_rt_prio(struct rt_rq *rt_rq, int prio)
{
        int prev_prio = rt_rq->highest_prio.curr;

        if (prio < prev_prio)
                rt_rq->highest_prio.curr = prio;

        inc_rt_prio_smp(rt_rq, prio, prev_prio);
}

static void
dec_rt_prio(struct rt_rq *rt_rq, int prio)
{
        int prev_prio = rt_rq->highest_prio.curr;

        if (rt_rq->rt_nr_running) {

                WARN_ON(prio < prev_prio);

                /*
                 * This may have been our highest task, and therefore
                 * we may have some recomputation to do
                 */
                if (prio == prev_prio) {
                        struct rt_prio_array *array = &rt_rq->active;

                        rt_rq->highest_prio.curr =
                                sched_find_first_bit(array->bitmap);
                }

        } else {
                rt_rq->highest_prio.curr = MAX_RT_PRIO-1;
        }

        dec_rt_prio_smp(rt_rq, prio, prev_prio);
}

#else

static inline void inc_rt_prio(struct rt_rq *rt_rq, int prio) {}
static inline void dec_rt_prio(struct rt_rq *rt_rq, int prio) {}

#endif /* CONFIG_SMP || CONFIG_RT_GROUP_SCHED */

#ifdef CONFIG_RT_GROUP_SCHED

static void
inc_rt_group(struct sched_rt_entity *rt_se, struct rt_rq *rt_rq)
{
        if (rt_se_boosted(rt_se))
                rt_rq->rt_nr_boosted++;

        if (rt_rq->tg)
                start_rt_bandwidth(&rt_rq->tg->rt_bandwidth);
}

static void
dec_rt_group(struct sched_rt_entity *rt_se, struct rt_rq *rt_rq)
{
        if (rt_se_boosted(rt_se))
                rt_rq->rt_nr_boosted--;

        WARN_ON(!rt_rq->rt_nr_running && rt_rq->rt_nr_boosted);
}

#else /* CONFIG_RT_GROUP_SCHED */

static void
inc_rt_group(struct sched_rt_entity *rt_se, struct rt_rq *rt_rq)
{
        start_rt_bandwidth(&def_rt_bandwidth);
}

static inline
void dec_rt_group(struct sched_rt_entity *rt_se, struct rt_rq *rt_rq) {}

#endif /* CONFIG_RT_GROUP_SCHED */

static inline
unsigned int rt_se_nr_running(struct sched_rt_entity *rt_se)
{
        struct rt_rq *group_rq = group_rt_rq(rt_se);

        if (group_rq)
                return group_rq->rt_nr_running;
        else
                return 1;
}

static inline
unsigned int rt_se_rr_nr_running(struct sched_rt_entity *rt_se)
{
        struct rt_rq *group_rq = group_rt_rq(rt_se);
        struct task_struct *tsk;

        if (group_rq)
                return group_rq->rr_nr_running;

        tsk = rt_task_of(rt_se);

        return (tsk->policy == SCHED_RR) ? 1 : 0;
}

static inline
void inc_rt_tasks(struct sched_rt_entity *rt_se, struct rt_rq *rt_rq)
{
        int prio = rt_se_prio(rt_se);

        WARN_ON(!rt_prio(prio));
        rt_rq->rt_nr_running += rt_se_nr_running(rt_se);
        rt_rq->rr_nr_running += rt_se_rr_nr_running(rt_se);

        inc_rt_prio(rt_rq, prio);
        inc_rt_migration(rt_se, rt_rq);
        inc_rt_group(rt_se, rt_rq);
}

static inline
void dec_rt_tasks(struct sched_rt_entity *rt_se, struct rt_rq *rt_rq)
{
        WARN_ON(!rt_prio(rt_se_prio(rt_se)));
        WARN_ON(!rt_rq->rt_nr_running);
        rt_rq->rt_nr_running -= rt_se_nr_running(rt_se);
        rt_rq->rr_nr_running -= rt_se_rr_nr_running(rt_se);

        dec_rt_prio(rt_rq, rt_se_prio(rt_se));
        dec_rt_migration(rt_se, rt_rq);
        dec_rt_group(rt_se, rt_rq);
}

/*
 * Change rt_se->run_list location unless SAVE && !MOVE
 *
 * assumes ENQUEUE/DEQUEUE flags match
 */
static inline bool move_entity(unsigned int flags)
{
        if ((flags & (DEQUEUE_SAVE | DEQUEUE_MOVE)) == DEQUEUE_SAVE)
                return false;

        return true;
}

static void __delist_rt_entity(struct sched_rt_entity *rt_se, struct rt_prio_array *array)
{
        list_del_init(&rt_se->run_list);

        if (list_empty(array->queue + rt_se_prio(rt_se)))
                __clear_bit(rt_se_prio(rt_se), array->bitmap);

        rt_se->on_list = 0;
}

static void __enqueue_rt_entity(struct sched_rt_entity *rt_se, unsigned int flags)
{
        struct rt_rq *rt_rq = rt_rq_of_se(rt_se);
        struct rt_prio_array *array = &rt_rq->active;
        struct rt_rq *group_rq = group_rt_rq(rt_se);
        struct list_head *queue = array->queue + rt_se_prio(rt_se);

        /*
         * Don't enqueue the group if its throttled, or when empty.
         * The latter is a consequence of the former when a child group
         * get throttled and the current group doesn't have any other
         * active members.
         */
        if (group_rq && (rt_rq_throttled(group_rq) || !group_rq->rt_nr_running)) {
                if (rt_se->on_list)
                        __delist_rt_entity(rt_se, array);
                return;
        }

        if (move_entity(flags)) {
                WARN_ON_ONCE(rt_se->on_list);
                if (flags & ENQUEUE_HEAD)
                        list_add(&rt_se->run_list, queue);
                else
                        list_add_tail(&rt_se->run_list, queue);

                __set_bit(rt_se_prio(rt_se), array->bitmap);
                rt_se->on_list = 1;
        }
        rt_se->on_rq = 1;

        inc_rt_tasks(rt_se, rt_rq);
}

static void __dequeue_rt_entity(struct sched_rt_entity *rt_se, unsigned int flags)
{
        struct rt_rq *rt_rq = rt_rq_of_se(rt_se);
        struct rt_prio_array *array = &rt_rq->active;

        if (move_entity(flags)) {
                WARN_ON_ONCE(!rt_se->on_list);
                __delist_rt_entity(rt_se, array);
        }
        rt_se->on_rq = 0;

        dec_rt_tasks(rt_se, rt_rq);
}

/*
 * Because the prio of an upper entry depends on the lower
 * entries, we must remove entries top - down.
 */
static void dequeue_rt_stack(struct sched_rt_entity *rt_se, unsigned int flags)
{
        struct sched_rt_entity *back = NULL;

        for_each_sched_rt_entity(rt_se) {
                rt_se->back = back;
                back = rt_se;
        }

        dequeue_top_rt_rq(rt_rq_of_se(back));

        for (rt_se = back; rt_se; rt_se = rt_se->back) {
                if (on_rt_rq(rt_se))
                        __dequeue_rt_entity(rt_se, flags);
        }
}

static void enqueue_rt_entity(struct sched_rt_entity *rt_se, unsigned int flags)
{
        struct rq *rq = rq_of_rt_se(rt_se);

        dequeue_rt_stack(rt_se, flags);
        for_each_sched_rt_entity(rt_se)
                __enqueue_rt_entity(rt_se, flags);
        enqueue_top_rt_rq(&rq->rt);
}

static void dequeue_rt_entity(struct sched_rt_entity *rt_se, unsigned int flags)
{
        struct rq *rq = rq_of_rt_se(rt_se);

        dequeue_rt_stack(rt_se, flags);

        for_each_sched_rt_entity(rt_se) {
                struct rt_rq *rt_rq = group_rt_rq(rt_se);

                if (rt_rq && rt_rq->rt_nr_running)
                        __enqueue_rt_entity(rt_se, flags);
        }
        enqueue_top_rt_rq(&rq->rt);
}

/*
 * Adding/removing a task to/from a priority array:
 */
static void
enqueue_task_rt(struct rq *rq, struct task_struct *p, int flags)
{
        struct sched_rt_entity *rt_se = &p->rt;

        if (flags & ENQUEUE_WAKEUP)
                rt_se->timeout = 0;

        enqueue_rt_entity(rt_se, flags);

        if (!task_current(rq, p) && p->nr_cpus_allowed > 1)
                enqueue_pushable_task(rq, p);
}

static void dequeue_task_rt(struct rq *rq, struct task_struct *p, int flags)
{
        struct sched_rt_entity *rt_se = &p->rt;

        update_curr_rt(rq);
        dequeue_rt_entity(rt_se, flags);

        dequeue_pushable_task(rq, p);
}

/*
 * Put task to the head or the end of the run list without the overhead of
 * dequeue followed by enqueue.
 */
static void
requeue_rt_entity(struct rt_rq *rt_rq, struct sched_rt_entity *rt_se, int head)
{
        if (on_rt_rq(rt_se)) {
                struct rt_prio_array *array = &rt_rq->active;
                struct list_head *queue = array->queue + rt_se_prio(rt_se);

                if (head)
                        list_move(&rt_se->run_list, queue);
                else
                        list_move_tail(&rt_se->run_list, queue);
        }
}

static void requeue_task_rt(struct rq *rq, struct task_struct *p, int head)
{
        struct sched_rt_entity *rt_se = &p->rt;
        struct rt_rq *rt_rq;

        for_each_sched_rt_entity(rt_se) {
                rt_rq = rt_rq_of_se(rt_se);
                requeue_rt_entity(rt_rq, rt_se, head);
        }
}

static void yield_task_rt(struct rq *rq)
{
        requeue_task_rt(rq, rq->curr, 0);
}

#ifdef CONFIG_SMP
static int find_lowest_rq(struct task_struct *task);

static int
select_task_rq_rt(struct task_struct *p, int cpu, int flags)
{
        struct task_struct *curr;
        struct rq *rq;
        bool test;

        /* For anything but wake ups, just return the task_cpu */
        if (!(flags & (WF_TTWU | WF_FORK)))
                goto out;

        rq = cpu_rq(cpu);

        rcu_read_lock();
        curr = READ_ONCE(rq->curr); /* unlocked access */

        /*
         * If the current task on @p's runqueue is an RT task, then
         * try to see if we can wake this RT task up on another
         * runqueue. Otherwise simply start this RT task
         * on its current runqueue.
         *
         * We want to avoid overloading runqueues. If the woken
         * task is a higher priority, then it will stay on this CPU
         * and the lower prio task should be moved to another CPU.
         * Even though this will probably make the lower prio task
         * lose its cache, we do not want to bounce a higher task
         * around just because it gave up its CPU, perhaps for a
         * lock?
         *
         * For equal prio tasks, we just let the scheduler sort it out.
         *
         * Otherwise, just let it ride on the affined RQ and the
         * post-schedule router will push the preempted task away
         *
         * This test is optimistic, if we get it wrong the load-balancer
         * will have to sort it out.
         *
         * We take into account the capacity of the CPU to ensure it fits the
         * requirement of the task - which is only important on heterogeneous
         * systems like big.LITTLE.
         */
        test = curr &&
               unlikely(rt_task(curr)) &&
               (curr->nr_cpus_allowed < 2 || curr->prio <= p->prio);

        if (test || !rt_task_fits_capacity(p, cpu)) {
                int target = find_lowest_rq(p);

                /*
                 * Bail out if we were forcing a migration to find a better
                 * fitting CPU but our search failed.
                 */
                if (!test && target != -1 && !rt_task_fits_capacity(p, target))
                        goto out_unlock;

                /*
                 * Don't bother moving it if the destination CPU is
                 * not running a lower priority task.
                 */
                if (target != -1 &&
                    p->prio < cpu_rq(target)->rt.highest_prio.curr)
                        cpu = target;
        }

out_unlock:
        rcu_read_unlock();

out:
        return cpu;
}

static void check_preempt_equal_prio(struct rq *rq, struct task_struct *p)
{
        /*
         * Current can't be migrated, useless to reschedule,
         * let's hope p can move out.
         */
        if (rq->curr->nr_cpus_allowed == 1 ||
            !cpupri_find(&rq->rd->cpupri, rq->curr, NULL))
                return;

        /*
         * p is migratable, so let's not schedule it and
         * see if it is pushed or pulled somewhere else.
         */
        if (p->nr_cpus_allowed != 1 &&
            cpupri_find(&rq->rd->cpupri, p, NULL))
                return;

        /*
         * There appear to be other CPUs that can accept
         * the current task but none can run 'p', so lets reschedule
         * to try and push the current task away:
         */
        requeue_task_rt(rq, p, 1);
        resched_curr(rq);
}

static int balance_rt(struct rq *rq, struct task_struct *p, struct rq_flags *rf)
{
        if (!on_rt_rq(&p->rt) && need_pull_rt_task(rq, p)) {
                /*
                 * 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've
                 * not yet started the picking loop.
                 */
                rq_unpin_lock(rq, rf);
                pull_rt_task(rq);
                rq_repin_lock(rq, rf);
        }

        return sched_stop_runnable(rq) || sched_dl_runnable(rq) || sched_rt_runnable(rq);
}
#endif /* CONFIG_SMP */

/*
 * Preempt the current task with a newly woken task if needed:
 */
static void check_preempt_curr_rt(struct rq *rq, struct task_struct *p, int flags)
{
        if (p->prio < rq->curr->prio) {
                resched_curr(rq);
                return;
        }

#ifdef CONFIG_SMP
        /*
         * If:
         *
         * - the newly woken task is of equal priority to the current task
         * - the newly woken task is non-migratable while current is migratable
         * - current will be preempted on the next reschedule
         *
         * we should check to see if current can readily move to a different
         * cpu.  If so, we will reschedule to allow the push logic to try
         * to move current somewhere else, making room for our non-migratable
         * task.
         */
        if (p->prio == rq->curr->prio && !test_tsk_need_resched(rq->curr))
                check_preempt_equal_prio(rq, p);
#endif
}

static inline void set_next_task_rt(struct rq *rq, struct task_struct *p, bool first)
{
        p->se.exec_start = rq_clock_task(rq);

        /* The running task is never eligible for pushing */
        dequeue_pushable_task(rq, p);

        if (!first)
                return;

        /*
         * If prev task was rt, put_prev_task() has already updated the
         * utilization. We only care of the case where we start to schedule a
         * rt task
         */
        if (rq->curr->sched_class != &rt_sched_class)
                update_rt_rq_load_avg(rq_clock_pelt(rq), rq, 0);

        rt_queue_push_tasks(rq);
}

static struct sched_rt_entity *pick_next_rt_entity(struct rq *rq,
                                                   struct rt_rq *rt_rq)
{
        struct rt_prio_array *array = &rt_rq->active;
        struct sched_rt_entity *next = NULL;
        struct list_head *queue;
        int idx;

        idx = sched_find_first_bit(array->bitmap);
        BUG_ON(idx >= MAX_RT_PRIO);

        queue = array->queue + idx;
        next = list_entry(queue->next, struct sched_rt_entity, run_list);

        return next;
}

static struct task_struct *_pick_next_task_rt(struct rq *rq)
{
        struct sched_rt_entity *rt_se;
        struct rt_rq *rt_rq  = &rq->rt;

        do {
                rt_se = pick_next_rt_entity(rq, rt_rq);
                BUG_ON(!rt_se);
                rt_rq = group_rt_rq(rt_se);
        } while (rt_rq);

        return rt_task_of(rt_se);
}

static struct task_struct *pick_task_rt(struct rq *rq)
{
        struct task_struct *p;

        if (!sched_rt_runnable(rq))
                return NULL;

        p = _pick_next_task_rt(rq);

        return p;
}

static struct task_struct *pick_next_task_rt(struct rq *rq)
{
        struct task_struct *p = pick_task_rt(rq);

        if (p)
                set_next_task_rt(rq, p, true);

        return p;
}

static void put_prev_task_rt(struct rq *rq, struct task_struct *p)
{
        update_curr_rt(rq);

        update_rt_rq_load_avg(rq_clock_pelt(rq), rq, 1);

        /*
         * The previous task needs to be made eligible for pushing
         * if it is still active
         */
        if (on_rt_rq(&p->rt) && p->nr_cpus_allowed > 1)
                enqueue_pushable_task(rq, p);
}

#ifdef CONFIG_SMP

/* Only try algorithms three times */
#define RT_MAX_TRIES 3

static int pick_rt_task(struct rq *rq, struct task_struct *p, int cpu)
{
        if (!task_running(rq, p) &&
            cpumask_test_cpu(cpu, &p->cpus_mask))
                return 1;

        return 0;
}

/*
 * Return the highest pushable rq's task, which is suitable to be executed
 * on the CPU, NULL otherwise
 */
static struct task_struct *pick_highest_pushable_task(struct rq *rq, int cpu)
{
        struct plist_head *head = &rq->rt.pushable_tasks;
        struct task_struct *p;

        if (!has_pushable_tasks(rq))
                return NULL;

        plist_for_each_entry(p, head, pushable_tasks) {
                if (pick_rt_task(rq, p, cpu))
                        return p;
        }

        return NULL;
}

static DEFINE_PER_CPU(cpumask_var_t, local_cpu_mask);

static int find_lowest_rq(struct task_struct *task)
{
        struct sched_domain *sd;
        struct cpumask *lowest_mask = this_cpu_cpumask_var_ptr(local_cpu_mask);
        int this_cpu = smp_processor_id();
        int cpu      = task_cpu(task);
        int ret;

        /* Make sure the mask is initialized first */
        if (unlikely(!lowest_mask))
                return -1;

        if (task->nr_cpus_allowed == 1)
                return -1; /* No other targets possible */

        /*
         * If we're on asym system ensure we consider the different capacities
         * of the CPUs when searching for the lowest_mask.
         */
        if (static_branch_unlikely(&sched_asym_cpucapacity)) {

                ret = cpupri_find_fitness(&task_rq(task)->rd->cpupri,
                                          task, lowest_mask,
                                          rt_task_fits_capacity);
        } else {

                ret = cpupri_find(&task_rq(task)->rd->cpupri,
                                  task, lowest_mask);
        }

        if (!ret)
                return -1; /* No targets found */

        /*
         * At this point we have built a mask of CPUs representing the
         * lowest priority tasks in the system.  Now we want to elect
         * the best one based on our affinity and topology.
         *
         * We prioritize the last CPU that the task executed on since
         * it is most likely cache-hot in that location.
         */
        if (cpumask_test_cpu(cpu, lowest_mask))
                return cpu;

        /*
         * Otherwise, we consult the sched_domains span maps to figure
         * out which CPU is logically closest to our hot cache data.
         */
        if (!cpumask_test_cpu(this_cpu, lowest_mask))
                this_cpu = -1; /* Skip this_cpu opt if not among lowest */

        rcu_read_lock();
        for_each_domain(cpu, sd) {
                if (sd->flags & SD_WAKE_AFFINE) {
                        int best_cpu;

                        /*
                         * "this_cpu" is cheaper to preempt than a
                         * remote processor.
                         */
                        if (this_cpu != -1 &&
                            cpumask_test_cpu(this_cpu, sched_domain_span(sd))) {
                                rcu_read_unlock();
                                return this_cpu;
                        }

                        best_cpu = cpumask_any_and_distribute(lowest_mask,
                                                              sched_domain_span(sd));
                        if (best_cpu < nr_cpu_ids) {
                                rcu_read_unlock();
                                return best_cpu;
                        }
                }
        }
        rcu_read_unlock();

        /*
         * And finally, if there were no matches within the domains
         * just give the caller *something* to work with from the compatible
         * locations.
         */
        if (this_cpu != -1)
                return this_cpu;

        cpu = cpumask_any_distribute(lowest_mask);
        if (cpu < nr_cpu_ids)
                return cpu;

        return -1;
}

/* Will lock the rq it finds */
static struct rq *find_lock_lowest_rq(struct task_struct *task, struct rq *rq)
{
        struct rq *lowest_rq = NULL;
        int tries;
        int cpu;

        for (tries = 0; tries < RT_MAX_TRIES; tries++) {
                cpu = find_lowest_rq(task);

                if ((cpu == -1) || (cpu == rq->cpu))
                        break;

                lowest_rq = cpu_rq(cpu);

                if (lowest_rq->rt.highest_prio.curr <= task->prio) {
                        /*
                         * Target rq has tasks of equal or higher priority,
                         * retrying does not release any lock and is unlikely
                         * to yield a different result.
                         */
                        lowest_rq = NULL;
                        break;
                }

                /* if the prio of this runqueue changed, try again */
                if (double_lock_balance(rq, lowest_rq)) {
                        /*
                         * We had to unlock the run queue. In
                         * the mean time, task could have
                         * migrated already or had its affinity changed.
                         * Also make sure that it wasn't scheduled on its rq.
                         */
                        if (unlikely(task_rq(task) != rq ||
                                     !cpumask_test_cpu(lowest_rq->cpu, &task->cpus_mask) ||
                                     task_running(rq, task) ||
                                     !rt_task(task) ||
                                     !task_on_rq_queued(task))) {

                                double_unlock_balance(rq, lowest_rq);
                                lowest_rq = NULL;
                                break;
                        }
                }

                /* If this rq is still suitable use it. */
                if (lowest_rq->rt.highest_prio.curr > task->prio)
                        break;

                /* try again */
                double_unlock_balance(rq, lowest_rq);
                lowest_rq = NULL;
        }

        return lowest_rq;
}

static struct task_struct *pick_next_pushable_task(struct rq *rq)
{
        struct task_struct *p;

        if (!has_pushable_tasks(rq))
                return NULL;

        p = plist_first_entry(&rq->rt.pushable_tasks,
                              struct task_struct, pushable_tasks);

        BUG_ON(rq->cpu != task_cpu(p));
        BUG_ON(task_current(rq, p));
        BUG_ON(p->nr_cpus_allowed <= 1);

        BUG_ON(!task_on_rq_queued(p));
        BUG_ON(!rt_task(p));

        return p;
}

/*
 * If the current CPU has more than one RT task, see if the non
 * running task can migrate over to a CPU that is running a task
 * of lesser priority.
 */
static int push_rt_task(struct rq *rq, bool pull)
{
        struct task_struct *next_task;
        struct rq *lowest_rq;
        int ret = 0;

        if (!rq->rt.overloaded)
                return 0;

        next_task = pick_next_pushable_task(rq);
        if (!next_task)
                return 0;

retry:
        if (is_migration_disabled(next_task)) {
                struct task_struct *push_task = NULL;
                int cpu;

                if (!pull || rq->push_busy)
                        return 0;

                cpu = find_lowest_rq(rq->curr);
                if (cpu == -1 || cpu == rq->cpu)
                        return 0;

                /*
                 * Given we found a CPU with lower priority than @next_task,
                 * therefore it should be running. However we cannot migrate it
                 * to this other CPU, instead attempt to push the current
                 * running task on this CPU away.
                 */
                push_task = get_push_task(rq);
                if (push_task) {
                        raw_spin_rq_unlock(rq);
                        stop_one_cpu_nowait(rq->cpu, push_cpu_stop,
                                            push_task, &rq->push_work);
                        raw_spin_rq_lock(rq);
                }

                return 0;
        }

        if (WARN_ON(next_task == rq->curr))
                return 0;

        /*
         * It's possible that the next_task slipped in of
         * higher priority than current. If that's the case
         * just reschedule current.
         */
        if (unlikely(next_task->prio < rq->curr->prio)) {
                resched_curr(rq);
                return 0;
        }

        /* We might release rq lock */
        get_task_struct(next_task);

        /* find_lock_lowest_rq locks the rq if found */
        lowest_rq = find_lock_lowest_rq(next_task, rq);
        if (!lowest_rq) {
                struct task_struct *task;
                /*
                 * find_lock_lowest_rq releases rq->lock
                 * so it is possible that next_task has migrated.
                 *
                 * We need to make sure that the task is still on the same
                 * run-queue and is also still the next task eligible for
                 * pushing.
                 */
                task = pick_next_pushable_task(rq);
                if (task == next_task) {
                        /*
                         * The task hasn't migrated, and is still the next
                         * eligible task, but we failed to find a run-queue
                         * to push it to.  Do not retry in this case, since
                         * other CPUs will pull from us when ready.
                         */
                        goto out;
                }

                if (!task)
                        /* No more tasks, just exit */
                        goto out;

                /*
                 * Something has shifted, try again.
                 */
                put_task_struct(next_task);
                next_task = task;
                goto retry;
        }

        deactivate_task(rq, next_task, 0);
        set_task_cpu(next_task, lowest_rq->cpu);
        activate_task(lowest_rq, next_task, 0);
        resched_curr(lowest_rq);
        ret = 1;

        double_unlock_balance(rq, lowest_rq);
out:
        put_task_struct(next_task);

        return ret;
}

static void push_rt_tasks(struct rq *rq)
{
        /* push_rt_task will return true if it moved an RT */
        while (push_rt_task(rq, false))
                ;
}

#ifdef HAVE_RT_PUSH_IPI

/*
 * When a high priority task schedules out from a CPU and a lower priority
 * task is scheduled in, a check is made to see if there's any RT tasks
 * on other CPUs that are waiting to run because a higher priority RT task
 * is currently running on its CPU. In this case, the CPU with multiple RT
 * tasks queued on it (overloaded) needs to be notified that a CPU has opened
 * up that may be able to run one of its non-running queued RT tasks.
 *
 * All CPUs with overloaded RT tasks need to be notified as there is currently
 * no way to know which of these CPUs have the highest priority task waiting
 * to run. Instead of trying to take a spinlock on each of these CPUs,
 * which has shown to cause large latency when done on machines with many
 * CPUs, sending an IPI to the CPUs to have them push off the overloaded
 * RT tasks waiting to run.
 *
 * Just sending an IPI to each of the CPUs is also an issue, as on large
 * count CPU machines, this can cause an IPI storm on a CPU, especially
 * if its the only CPU with multiple RT tasks queued, and a large number
 * of CPUs scheduling a lower priority task at the same time.
 *
 * Each root domain has its own irq work function that can iterate over
 * all CPUs with RT overloaded tasks. Since all CPUs with overloaded RT
 * task must be checked if there's one or many CPUs that are lowering
 * their priority, there's a single irq work iterator that will try to
 * push off RT tasks that are waiting to run.
 *
 * When a CPU schedules a lower priority task, it will kick off the
 * irq work iterator that will jump to each CPU with overloaded RT tasks.
 * As it only takes the first CPU that schedules a lower priority task
 * to start the process, the rto_start variable is incremented and if
 * the atomic result is one, then that CPU will try to take the rto_lock.
 * This prevents high contention on the lock as the process handles all
 * CPUs scheduling lower priority tasks.
 *
 * All CPUs that are scheduling a lower priority task will increment the
 * rt_loop_next variable. This will make sure that the irq work iterator
 * checks all RT overloaded CPUs whenever a CPU schedules a new lower
 * priority task, even if the iterator is in the middle of a scan. Incrementing
 * the rt_loop_next will cause the iterator to perform another scan.
 *
 */
static int rto_next_cpu(struct root_domain *rd)
{
        int next;
        int cpu;

        /*
         * When starting the IPI RT pushing, the rto_cpu is set to -1,
         * rt_next_cpu() will simply return the first CPU found in
         * the rto_mask.
         *
         * If rto_next_cpu() is called with rto_cpu is a valid CPU, it
         * will return the next CPU found in the rto_mask.
         *
         * If there are no more CPUs left in the rto_mask, then a check is made
         * against rto_loop and rto_loop_next. rto_loop is only updated with
         * the rto_lock held, but any CPU may increment the rto_loop_next
         * without any locking.
         */
        for (;;) {

                /* When rto_cpu is -1 this acts like cpumask_first() */
                cpu = cpumask_next(rd->rto_cpu, rd->rto_mask);

                rd->rto_cpu = cpu;

                if (cpu < nr_cpu_ids)
                        return cpu;

                rd->rto_cpu = -1;

                /*
                 * ACQUIRE ensures we see the @rto_mask changes
                 * made prior to the @next value observed.
                 *
                 * Matches WMB in rt_set_overload().
                 */
                next = atomic_read_acquire(&rd->rto_loop_next);

                if (rd->rto_loop == next)
                        break;

                rd->rto_loop = next;
        }

        return -1;
}

static inline bool rto_start_trylock(atomic_t *v)
{
        return !atomic_cmpxchg_acquire(v, 0, 1);
}

static inline void rto_start_unlock(atomic_t *v)
{
        atomic_set_release(v, 0);
}

static void tell_cpu_to_push(struct rq *rq)
{
        int cpu = -1;

        /* Keep the loop going if the IPI is currently active */
        atomic_inc(&rq->rd->rto_loop_next);

        /* Only one CPU can initiate a loop at a time */
        if (!rto_start_trylock(&rq->rd->rto_loop_start))
                return;

        raw_spin_lock(&rq->rd->rto_lock);

        /*
         * The rto_cpu is updated under the lock, if it has a valid CPU
         * then the IPI is still running and will continue due to the
         * update to loop_next, and nothing needs to be done here.
         * Otherwise it is finishing up and an ipi needs to be sent.
         */
        if (rq->rd->rto_cpu < 0)
                cpu = rto_next_cpu(rq->rd);

        raw_spin_unlock(&rq->rd->rto_lock);

        rto_start_unlock(&rq->rd->rto_loop_start);

        if (cpu >= 0) {
                /* Make sure the rd does not get freed while pushing */
                sched_get_rd(rq->rd);
                irq_work_queue_on(&rq->rd->rto_push_work, cpu);
        }
}

/* Called from hardirq context */
void rto_push_irq_work_func(struct irq_work *work)
{
        struct root_domain *rd =
                container_of(work, struct root_domain, rto_push_work);
        struct rq *rq;
        int cpu;

        rq = this_rq();

        /*
         * We do not need to grab the lock to check for has_pushable_tasks.
         * When it gets updated, a check is made if a push is possible.
         */
        if (has_pushable_tasks(rq)) {
                raw_spin_rq_lock(rq);
                while (push_rt_task(rq, true))
                        ;
                raw_spin_rq_unlock(rq);
        }

        raw_spin_lock(&rd->rto_lock);

        /* Pass the IPI to the next rt overloaded queue */
        cpu = rto_next_cpu(rd);

        raw_spin_unlock(&rd->rto_lock);

        if (cpu < 0) {
                sched_put_rd(rd);
                return;
        }

        /* Try the next RT overloaded CPU */
        irq_work_queue_on(&rd->rto_push_work, cpu);
}
#endif /* HAVE_RT_PUSH_IPI */

static void pull_rt_task(struct rq *this_rq)
{
        int this_cpu = this_rq->cpu, cpu;
        bool resched = false;
        struct task_struct *p, *push_task;
        struct rq *src_rq;
        int rt_overload_count = rt_overloaded(this_rq);

        if (likely(!rt_overload_count))
                return;

        /*
         * Match the barrier from rt_set_overloaded; this guarantees that if we
         * see overloaded we must also see the rto_mask bit.
         */
        smp_rmb();

        /* If we are the only overloaded CPU do nothing */
        if (rt_overload_count == 1 &&
            cpumask_test_cpu(this_rq->cpu, this_rq->rd->rto_mask))
                return;

#ifdef HAVE_RT_PUSH_IPI
        if (sched_feat(RT_PUSH_IPI)) {
                tell_cpu_to_push(this_rq);
                return;
        }
#endif

        for_each_cpu(cpu, this_rq->rd->rto_mask) {
                if (this_cpu == cpu)
                        continue;

                src_rq = cpu_rq(cpu);

                /*
                 * Don't bother taking the src_rq->lock if the next highest
                 * task is known to be lower-priority than our current task.
                 * This may look racy, but if this value is about to go
                 * logically higher, the src_rq will push this task away.
                 * And if its going logically lower, we do not care
                 */
                if (src_rq->rt.highest_prio.next >=
                    this_rq->rt.highest_prio.curr)
                        continue;

                /*
                 * We can potentially drop this_rq's lock in
                 * double_lock_balance, and another CPU could
                 * alter this_rq
                 */
                push_task = NULL;
                double_lock_balance(this_rq, src_rq);

                /*
                 * We can pull only a task, which is pushable
                 * on its rq, and no others.
                 */
                p = pick_highest_pushable_task(src_rq, this_cpu);

                /*
                 * Do we have an RT task that preempts
                 * the to-be-scheduled task?
                 */
                if (p && (p->prio < this_rq->rt.highest_prio.curr)) {
                        WARN_ON(p == src_rq->curr);
                        WARN_ON(!task_on_rq_queued(p));

                        /*
                         * There's a chance that p is higher in priority
                         * than what's currently running on its CPU.
                         * This is just that p is waking up and hasn't
                         * had a chance to schedule. We only pull
                         * p if it is lower in priority than the
                         * current task on the run queue
                         */
                        if (p->prio < src_rq->curr->prio)
                                goto skip;

                        if (is_migration_disabled(p)) {
                                push_task = get_push_task(src_rq);
                        } else {
                                deactivate_task(src_rq, p, 0);
                                set_task_cpu(p, this_cpu);
                                activate_task(this_rq, p, 0);
                                resched = true;
                        }
                        /*
                         * We continue with the search, just in
                         * case there's an even higher prio task
                         * in another runqueue. (low likelihood
                         * but possible)
                         */
                }
skip:
                double_unlock_balance(this_rq, src_rq);

                if (push_task) {
                        raw_spin_rq_unlock(this_rq);
                        stop_one_cpu_nowait(src_rq->cpu, push_cpu_stop,
                                            push_task, &src_rq->push_work);
                        raw_spin_rq_lock(this_rq);
                }
        }

        if (resched)
                resched_curr(this_rq);
}

/*
 * If we are not running and we are not going to reschedule soon, we should
 * try to push tasks away now
 */
static void task_woken_rt(struct rq *rq, struct task_struct *p)
{
        bool need_to_push = !task_running(rq, p) &&
                            !test_tsk_need_resched(rq->curr) &&
                            p->nr_cpus_allowed > 1 &&
                            (dl_task(rq->curr) || rt_task(rq->curr)) &&
                            (rq->curr->nr_cpus_allowed < 2 ||
                             rq->curr->prio <= p->prio);

        if (need_to_push)
                push_rt_tasks(rq);
}

/* Assumes rq->lock is held */
static void rq_online_rt(struct rq *rq)
{
        if (rq->rt.overloaded)
                rt_set_overload(rq);

        __enable_runtime(rq);

        cpupri_set(&rq->rd->cpupri, rq->cpu, rq->rt.highest_prio.curr);
}

/* Assumes rq->lock is held */
static void rq_offline_rt(struct rq *rq)
{
        if (rq->rt.overloaded)
                rt_clear_overload(rq);

        __disable_runtime(rq);

        cpupri_set(&rq->rd->cpupri, rq->cpu, CPUPRI_INVALID);
}

/*
 * When switch from the rt queue, we bring ourselves to a position
 * that we might want to pull RT tasks from other runqueues.
 */
static void switched_from_rt(struct rq *rq, struct task_struct *p)
{
        /*
         * If there are other RT tasks then we will reschedule
         * and the scheduling of the other RT tasks will handle
         * the balancing. But if we are the last RT task
         * we may need to handle the pulling of RT tasks
         * now.
         */
        if (!task_on_rq_queued(p) || rq->rt.rt_nr_running)
                return;

        rt_queue_pull_task(rq);
}

void __init init_sched_rt_class(void)
{
        unsigned int i;

        for_each_possible_cpu(i) {
                zalloc_cpumask_var_node(&per_cpu(local_cpu_mask, i),
                                        GFP_KERNEL, cpu_to_node(i));
        }
}
#endif /* CONFIG_SMP */

/*
 * When switching a task to RT, we may overload the runqueue
 * with RT tasks. In this case we try to push them off to
 * other runqueues.
 */
static void switched_to_rt(struct rq *rq, struct task_struct *p)
{
        /*
         * If we are running, update the avg_rt tracking, as the running time
         * will now on be accounted into the latter.
         */
        if (task_current(rq, p)) {
                update_rt_rq_load_avg(rq_clock_pelt(rq), rq, 0);
                return;
        }

        /*
         * If we are not running we may need to preempt the current
         * running task. If that current running task is also an RT task
         * then see if we can move to another run queue.
         */
        if (task_on_rq_queued(p)) {
#ifdef CONFIG_SMP
                if (p->nr_cpus_allowed > 1 && rq->rt.overloaded)
                        rt_queue_push_tasks(rq);
#endif /* CONFIG_SMP */
                if (p->prio < rq->curr->prio && cpu_online(cpu_of(rq)))
                        resched_curr(rq);
        }
}

/*
 * Priority of the task has changed. This may cause
 * us to initiate a push or pull.
 */
static void
prio_changed_rt(struct rq *rq, struct task_struct *p, int oldprio)
{
        if (!task_on_rq_queued(p))
                return;

        if (task_current(rq, p)) {
#ifdef CONFIG_SMP
                /*
                 * If our priority decreases while running, we
                 * may need to pull tasks to this runqueue.
                 */
                if (oldprio < p->prio)
                        rt_queue_pull_task(rq);

                /*
                 * If there's a higher priority task waiting to run
                 * then reschedule.
                 */
                if (p->prio > rq->rt.highest_prio.curr)
                        resched_curr(rq);
#else
                /* For UP simply resched on drop of prio */
                if (oldprio < p->prio)
                        resched_curr(rq);
#endif /* CONFIG_SMP */
        } else {
                /*
                 * This task is not running, but if it is
                 * greater than the current running task
                 * then reschedule.
                 */
                if (p->prio < rq->curr->prio)
                        resched_curr(rq);
        }
}

#ifdef CONFIG_POSIX_TIMERS
static void watchdog(struct rq *rq, struct task_struct *p)
{
        unsigned long soft, hard;

        /* max may change after cur was read, this will be fixed next tick */
        soft = task_rlimit(p, RLIMIT_RTTIME);
        hard = task_rlimit_max(p, RLIMIT_RTTIME);

        if (soft != RLIM_INFINITY) {
                unsigned long next;

                if (p->rt.watchdog_stamp != jiffies) {
                        p->rt.timeout++;
                        p->rt.watchdog_stamp = jiffies;
                }

                next = DIV_ROUND_UP(min(soft, hard), USEC_PER_SEC/HZ);
                if (p->rt.timeout > next) {
                        posix_cputimers_rt_watchdog(&p->posix_cputimers,
                                                    p->se.sum_exec_runtime);
                }
        }
}
#else
static inline void watchdog(struct rq *rq, struct task_struct *p) { }
#endif

/*
 * 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_rt(struct rq *rq, struct task_struct *p, int queued)
{
        struct sched_rt_entity *rt_se = &p->rt;

        update_curr_rt(rq);
        update_rt_rq_load_avg(rq_clock_pelt(rq), rq, 1);

        watchdog(rq, p);

        /*
         * RR tasks need a special form of timeslice management.
         * FIFO tasks have no timeslices.
         */
        if (p->policy != SCHED_RR)
                return;

        if (--p->rt.time_slice)
                return;

        p->rt.time_slice = sched_rr_timeslice;

        /*
         * Requeue to the end of queue if we (and all of our ancestors) are not
         * the only element on the queue
         */
        for_each_sched_rt_entity(rt_se) {
                if (rt_se->run_list.prev != rt_se->run_list.next) {
                        requeue_task_rt(rq, p, 0);
                        resched_curr(rq);
                        return;
                }
        }
}

static unsigned int get_rr_interval_rt(struct rq *rq, struct task_struct *task)
{
        /*
         * Time slice is 0 for SCHED_FIFO tasks
         */
        if (task->policy == SCHED_RR)
                return sched_rr_timeslice;
        else
                return 0;
}

DEFINE_SCHED_CLASS(rt) = {

        .enqueue_task           = enqueue_task_rt,
        .dequeue_task           = dequeue_task_rt,
        .yield_task             = yield_task_rt,

        .check_preempt_curr     = check_preempt_curr_rt,

        .pick_next_task         = pick_next_task_rt,
        .put_prev_task          = put_prev_task_rt,
        .set_next_task          = set_next_task_rt,

#ifdef CONFIG_SMP
        .balance                = balance_rt,
        .pick_task              = pick_task_rt,
        .select_task_rq         = select_task_rq_rt,
        .set_cpus_allowed       = set_cpus_allowed_common,
        .rq_online              = rq_online_rt,
        .rq_offline             = rq_offline_rt,
        .task_woken             = task_woken_rt,
        .switched_from          = switched_from_rt,
        .find_lock_rq           = find_lock_lowest_rq,
#endif

        .task_tick              = task_tick_rt,

        .get_rr_interval        = get_rr_interval_rt,

        .prio_changed           = prio_changed_rt,
        .switched_to            = switched_to_rt,

        .update_curr            = update_curr_rt,

#ifdef CONFIG_UCLAMP_TASK
        .uclamp_enabled         = 1,
#endif
};

#ifdef CONFIG_RT_GROUP_SCHED
/*
 * Ensure that the real time constraints are schedulable.
 */
static DEFINE_MUTEX(rt_constraints_mutex);

static inline int tg_has_rt_tasks(struct task_group *tg)
{
        struct task_struct *task;
        struct css_task_iter it;
        int ret = 0;

        /*
         * Autogroups do not have RT tasks; see autogroup_create().
         */
        if (task_group_is_autogroup(tg))
                return 0;

        css_task_iter_start(&tg->css, 0, &it);
        while (!ret && (task = css_task_iter_next(&it)))
                ret |= rt_task(task);
        css_task_iter_end(&it);

        return ret;
}

struct rt_schedulable_data {
        struct task_group *tg;
        u64 rt_period;
        u64 rt_runtime;
};

static int tg_rt_schedulable(struct task_group *tg, void *data)
{
        struct rt_schedulable_data *d = data;
        struct task_group *child;
        unsigned long total, sum = 0;
        u64 period, runtime;

        period = ktime_to_ns(tg->rt_bandwidth.rt_period);
        runtime = tg->rt_bandwidth.rt_runtime;

        if (tg == d->tg) {
                period = d->rt_period;
                runtime = d->rt_runtime;
        }

        /*
         * Cannot have more runtime than the period.
         */
        if (runtime > period && runtime != RUNTIME_INF)
                return -EINVAL;

        /*
         * Ensure we don't starve existing RT tasks if runtime turns zero.
         */
        if (rt_bandwidth_enabled() && !runtime &&
            tg->rt_bandwidth.rt_runtime && tg_has_rt_tasks(tg))
                return -EBUSY;

        total = to_ratio(period, runtime);

        /*
         * Nobody can have more than the global setting allows.
         */
        if (total > to_ratio(global_rt_period(), global_rt_runtime()))
                return -EINVAL;

        /*
         * The sum of our children's runtime should not exceed our own.
         */
        list_for_each_entry_rcu(child, &tg->children, siblings) {
                period = ktime_to_ns(child->rt_bandwidth.rt_period);
                runtime = child->rt_bandwidth.rt_runtime;

                if (child == d->tg) {
                        period = d->rt_period;
                        runtime = d->rt_runtime;
                }

                sum += to_ratio(period, runtime);
        }

        if (sum > total)
                return -EINVAL;

        return 0;
}

static int __rt_schedulable(struct task_group *tg, u64 period, u64 runtime)
{
        int ret;

        struct rt_schedulable_data data = {
                .tg = tg,
                .rt_period = period,
                .rt_runtime = runtime,
        };

        rcu_read_lock();
        ret = walk_tg_tree(tg_rt_schedulable, tg_nop, &data);
        rcu_read_unlock();

        return ret;
}

static int tg_set_rt_bandwidth(struct task_group *tg,
                u64 rt_period, u64 rt_runtime)
{
        int i, err = 0;

        /*
         * Disallowing the root group RT runtime is BAD, it would disallow the
         * kernel creating (and or operating) RT threads.
         */
        if (tg == &root_task_group && rt_runtime == 0)
                return -EINVAL;

        /* No period doesn't make any sense. */
        if (rt_period == 0)
                return -EINVAL;

        /*
         * Bound quota to defend quota against overflow during bandwidth shift.
         */
        if (rt_runtime != RUNTIME_INF && rt_runtime > max_rt_runtime)
                return -EINVAL;

        mutex_lock(&rt_constraints_mutex);
        err = __rt_schedulable(tg, rt_period, rt_runtime);
        if (err)
                goto unlock;

        raw_spin_lock_irq(&tg->rt_bandwidth.rt_runtime_lock);
        tg->rt_bandwidth.rt_period = ns_to_ktime(rt_period);
        tg->rt_bandwidth.rt_runtime = rt_runtime;

        for_each_possible_cpu(i) {
                struct rt_rq *rt_rq = tg->rt_rq[i];

                raw_spin_lock(&rt_rq->rt_runtime_lock);
                rt_rq->rt_runtime = rt_runtime;
                raw_spin_unlock(&rt_rq->rt_runtime_lock);
        }
        raw_spin_unlock_irq(&tg->rt_bandwidth.rt_runtime_lock);
unlock:
        mutex_unlock(&rt_constraints_mutex);

        return err;
}

int sched_group_set_rt_runtime(struct task_group *tg, long rt_runtime_us)
{
        u64 rt_runtime, rt_period;

        rt_period = ktime_to_ns(tg->rt_bandwidth.rt_period);
        rt_runtime = (u64)rt_runtime_us * NSEC_PER_USEC;
        if (rt_runtime_us < 0)
                rt_runtime = RUNTIME_INF;
        else if ((u64)rt_runtime_us > U64_MAX / NSEC_PER_USEC)
                return -EINVAL;

        return tg_set_rt_bandwidth(tg, rt_period, rt_runtime);
}

long sched_group_rt_runtime(struct task_group *tg)
{
        u64 rt_runtime_us;

        if (tg->rt_bandwidth.rt_runtime == RUNTIME_INF)
                return -1;

        rt_runtime_us = tg->rt_bandwidth.rt_runtime;
        do_div(rt_runtime_us, NSEC_PER_USEC);
        return rt_runtime_us;
}

int sched_group_set_rt_period(struct task_group *tg, u64 rt_period_us)
{
        u64 rt_runtime, rt_period;

        if (rt_period_us > U64_MAX / NSEC_PER_USEC)
                return -EINVAL;

        rt_period = rt_period_us * NSEC_PER_USEC;
        rt_runtime = tg->rt_bandwidth.rt_runtime;

        return tg_set_rt_bandwidth(tg, rt_period, rt_runtime);
}

long sched_group_rt_period(struct task_group *tg)
{
        u64 rt_period_us;

        rt_period_us = ktime_to_ns(tg->rt_bandwidth.rt_period);
        do_div(rt_period_us, NSEC_PER_USEC);
        return rt_period_us;
}

static int sched_rt_global_constraints(void)
{
        int ret = 0;

        mutex_lock(&rt_constraints_mutex);
        ret = __rt_schedulable(NULL, 0, 0);
        mutex_unlock(&rt_constraints_mutex);

        return ret;
}

int sched_rt_can_attach(struct task_group *tg, struct task_struct *tsk)
{
        /* Don't accept realtime tasks when there is no way for them to run */
        if (rt_task(tsk) && tg->rt_bandwidth.rt_runtime == 0)
                return 0;

        return 1;
}

#else /* !CONFIG_RT_GROUP_SCHED */
static int sched_rt_global_constraints(void)
{
        unsigned long flags;
        int i;

        raw_spin_lock_irqsave(&def_rt_bandwidth.rt_runtime_lock, flags);
        for_each_possible_cpu(i) {
                struct rt_rq *rt_rq = &cpu_rq(i)->rt;

                raw_spin_lock(&rt_rq->rt_runtime_lock);
                rt_rq->rt_runtime = global_rt_runtime();
                raw_spin_unlock(&rt_rq->rt_runtime_lock);
        }
        raw_spin_unlock_irqrestore(&def_rt_bandwidth.rt_runtime_lock, flags);

        return 0;
}
#endif /* CONFIG_RT_GROUP_SCHED */

static int sched_rt_global_validate(void)
{
        if (sysctl_sched_rt_period <= 0)
                return -EINVAL;

        if ((sysctl_sched_rt_runtime != RUNTIME_INF) &&
                ((sysctl_sched_rt_runtime > sysctl_sched_rt_period) ||
                 ((u64)sysctl_sched_rt_runtime *
                        NSEC_PER_USEC > max_rt_runtime)))
                return -EINVAL;

        return 0;
}

static void sched_rt_do_global(void)
{
        def_rt_bandwidth.rt_runtime = global_rt_runtime();
        def_rt_bandwidth.rt_period = ns_to_ktime(global_rt_period());
}

int sched_rt_handler(struct ctl_table *table, int write, void *buffer,
                size_t *lenp, loff_t *ppos)
{
        int old_period, old_runtime;
        static DEFINE_MUTEX(mutex);
        int ret;

        mutex_lock(&mutex);
        old_period = sysctl_sched_rt_period;
        old_runtime = sysctl_sched_rt_runtime;

        ret = proc_dointvec(table, write, buffer, lenp, ppos);

        if (!ret && write) {
                ret = sched_rt_global_validate();
                if (ret)
                        goto undo;

                ret = sched_dl_global_validate();
                if (ret)
                        goto undo;

                ret = sched_rt_global_constraints();
                if (ret)
                        goto undo;

                sched_rt_do_global();
                sched_dl_do_global();
        }
        if (0) {
undo:
                sysctl_sched_rt_period = old_period;
                sysctl_sched_rt_runtime = old_runtime;
        }
        mutex_unlock(&mutex);

        return ret;
}

int sched_rr_handler(struct ctl_table *table, int write, void *buffer,
                size_t *lenp, loff_t *ppos)
{
        int ret;
        static DEFINE_MUTEX(mutex);

        mutex_lock(&mutex);
        ret = proc_dointvec(table, write, buffer, lenp, ppos);
        /*
         * Make sure that internally we keep jiffies.
         * Also, writing zero resets the timeslice to default:
         */
        if (!ret && write) {
                sched_rr_timeslice =
                        sysctl_sched_rr_timeslice <= 0 ? RR_TIMESLICE :
                        msecs_to_jiffies(sysctl_sched_rr_timeslice);
        }
        mutex_unlock(&mutex);

        return ret;
}

#ifdef CONFIG_SCHED_DEBUG
void print_rt_stats(struct seq_file *m, int cpu)
{
        rt_rq_iter_t iter;
        struct rt_rq *rt_rq;

        rcu_read_lock();
        for_each_rt_rq(rt_rq, iter, cpu_rq(cpu))
                print_rt_rq(m, cpu, rt_rq);
        rcu_read_unlock();
}
#endif /* CONFIG_SCHED_DEBUG */