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Subject[tip:sched/core] sched/fair: Avoid calling sync_entity_load_avg() unnecessarily
Commit-ID:  c976a862ba4869c1e75c39b9b8f1e9ebfe90cdfc
Gitweb: https://git.kernel.org/tip/c976a862ba4869c1e75c39b9b8f1e9ebfe90cdfc
Author: Viresh Kumar <viresh.kumar@linaro.org>
AuthorDate: Thu, 26 Apr 2018 16:00:51 +0530
Committer: Ingo Molnar <mingo@kernel.org>
CommitDate: Fri, 4 May 2018 10:00:08 +0200

sched/fair: Avoid calling sync_entity_load_avg() unnecessarily

Call sync_entity_load_avg() directly from find_idlest_cpu() instead of
select_task_rq_fair(), as that's where we need to use task's utilization
value. And call sync_entity_load_avg() only after making sure sched
domain spans over one of the allowed CPUs for the task.

Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Vincent Guittot <vincent.guittot@linaro.org>
Link: http://lkml.kernel.org/r/cd019d1753824c81130eae7b43e2bbcec47cc1ad.1524738578.git.viresh.kumar@linaro.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>
---
kernel/sched/fair.c | 16 +++++++---------
1 file changed, 7 insertions(+), 9 deletions(-)

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 4b346f358005..1f6a23a5b451 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -6199,6 +6199,13 @@ static inline int find_idlest_cpu(struct sched_domain *sd, struct task_struct *p
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;
@@ -6651,15 +6658,6 @@ select_task_rq_fair(struct task_struct *p, int prev_cpu, int sd_flag, int wake_f

if (unlikely(sd)) {
/* Slow path */
-
- /*
- * We're going to need the task's util for capacity_spare_wake
- * in find_idlest_group. Sync it up to prev_cpu's
- * last_update_time.
- */
- if (!(sd_flag & SD_BALANCE_FORK))
- sync_entity_load_avg(&p->se);
-
new_cpu = find_idlest_cpu(sd, p, cpu, prev_cpu, sd_flag);
} else if (sd_flag & SD_BALANCE_WAKE) { /* XXX always ? */
/* Fast path */
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