linux-kernel - [PATCH 2/2] sched/fair: Avoid calling sync_entity_load

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Message-Id: <cd019d1753824c81130eae7b43e2bbcec47cc1ad.1524738578.git.viresh.kumar@linaro.org>
Date:   Thu, 26 Apr 2018 16:00:51 +0530
From:   Viresh Kumar <viresh.kumar@...aro.org>
To:     Ingo Molnar <mingo@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>
Cc:     Viresh Kumar <viresh.kumar@...aro.org>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        linux-kernel@...r.kernel.org
Subject: [PATCH 2/2] 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@...aro.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 84fc74ddbd4b..5b1b4f91f132 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 */
-- 
2.15.0.194.g9af6a3dea062