[PATCH 2/3] sched/fair: util_est: update before schedutil

[Patrick Bellasi]

When a task is enqueue the estimated utilization of a CPU is updated
to better support the selection of the required frequency.
However, schedutil is (implicitly) updated by update_load_avg() which
always happens before util_est_{en,de}queue(), thus potentially
introducing a latency between estimated utilization updates and
frequency selections.

Let's update util_est at the beginning of enqueue_task_fair(),
which will ensure that all schedutil updates will see the most
updated estimated utilization value for a CPU.

Reported-by: Vincent Guittot <vincent.guittot@xxxxxxxxxx>
Signed-off-by: Patrick Bellasi <patrick.bellasi@xxxxxxx>
Cc: Ingo Molnar <mingo@xxxxxxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Cc: Vincent Guittot <vincent.guittot@xxxxxxxxxx>
Cc: linux-kernel@xxxxxxxxxxxxxxx
Cc: linux-pm@xxxxxxxxxxxxxxx
---
 kernel/sched/fair.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 1f6a23a5b451..01dfc47541e6 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -5356,6 +5356,9 @@ enqueue_task_fair(struct rq *rq, struct task_struct *p, int flags)
 	struct cfs_rq *cfs_rq;
 	struct sched_entity *se = &p->se;
 
+	/* Estimated utilization must be updated before schedutil */
+	util_est_enqueue(&rq->cfs, p);
+
 	/*
 	 * If in_iowait is set, the code below may not trigger any cpufreq
 	 * utilization updates, so do it here explicitly with the IOWAIT flag
@@ -5397,7 +5400,6 @@ enqueue_task_fair(struct rq *rq, struct task_struct *p, int flags)
 	if (!se)
 		add_nr_running(rq, 1);
 
-	util_est_enqueue(&rq->cfs, p);
 	hrtick_update(rq);
 }
 
-- 
2.15.1