sched/fair: Restructure wake_affine*() to return a CPU id

This is a preparation patch that has wake_affine*() return a CPU ID instead of
a boolean. The intent is to allow the wake_affine() helpers to be avoided
if a decision is already made. This patch has no functional change.

Signed-off-by: Mel Gorman <mgorman@techsingularity.net>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Matt Fleming <matt@codeblueprint.co.uk>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/20180130104555.4125-3-mgorman@techsingularity.net
Signed-off-by: Ingo Molnar <mingo@kernel.org>

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 0a551df..4c400d7 100644 (file)
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -5692,7 +5692,7 @@ static int wake_wide(struct task_struct *p)
  *                       scheduling latency of the CPUs. This seems to work
  *                       for the overloaded case.
  */
-static bool
+static int
 wake_affine_idle(int this_cpu, int prev_cpu, int sync)
 {
        /*
@@ -5702,15 +5702,15 @@ wake_affine_idle(int this_cpu, int prev_cpu, int sync)
         * node depending on the IO topology or IRQ affinity settings.
         */
        if (idle_cpu(this_cpu) && cpus_share_cache(this_cpu, prev_cpu))
-               return true;
+               return this_cpu;
 
        if (sync && cpu_rq(this_cpu)->nr_running == 1)
-               return true;
+               return this_cpu;
 
-       return false;
+       return nr_cpumask_bits;
 }
 
-static bool
+static int
 wake_affine_weight(struct sched_domain *sd, struct task_struct *p,
                   int this_cpu, int prev_cpu, int sync)
 {
@@ -5724,7 +5724,7 @@ wake_affine_weight(struct sched_domain *sd, struct task_struct *p,
                unsigned long current_load = task_h_load(current);
 
                if (current_load > this_eff_load)
-                       return true;
+                       return this_cpu;
 
                this_eff_load -= current_load;
        }
@@ -5741,28 +5741,28 @@ wake_affine_weight(struct sched_domain *sd, struct task_struct *p,
                prev_eff_load *= 100 + (sd->imbalance_pct - 100) / 2;
        prev_eff_load *= capacity_of(this_cpu);
 
-       return this_eff_load <= prev_eff_load;
+       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 prev_cpu, int sync)
 {
        int this_cpu = smp_processor_id();
-       bool affine = false;
+       int target = nr_cpumask_bits;
 
        if (sched_feat(WA_IDLE))
-               affine = wake_affine_idle(this_cpu, prev_cpu, sync);
+               target = wake_affine_idle(this_cpu, prev_cpu, sync);
 
-       if (sched_feat(WA_WEIGHT) && !affine)
-               affine = wake_affine_weight(sd, p, 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 (affine) {
-               schedstat_inc(sd->ttwu_move_affine);
-               schedstat_inc(p->se.statistics.nr_wakeups_affine);
-       }
+       if (target == nr_cpumask_bits)
+               return prev_cpu;
 
-       return affine;
+       schedstat_inc(sd->ttwu_move_affine);
+       schedstat_inc(p->se.statistics.nr_wakeups_affine);
+       return target;
 }
 
 static inline unsigned long task_util(struct task_struct *p);
@@ -6355,8 +6355,7 @@ select_task_rq_fair(struct task_struct *p, int prev_cpu, int sd_flag, int wake_f
                if (cpu == prev_cpu)
                        goto pick_cpu;
 
-               if (wake_affine(affine_sd, p, prev_cpu, sync))
-                       new_cpu = cpu;
+               new_cpu = wake_affine(affine_sd, p, prev_cpu, sync);
        }
 
        if (sd && !(sd_flag & SD_BALANCE_FORK)) {