Commit 2539fc82 authored May 24, 2018 by Patrick Bellasi Committed by Ingo Molnar May 25, 2018

sched/fair: Update util_est before updating schedutil



When a task is enqueued 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@linaro.org>
Signed-off-by: Patrick Bellasi <patrick.bellasi@arm.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Thomas Gleixner <tglx@linutronix.de>
Acked-by: Viresh Kumar <viresh.kumar@linaro.org>
Acked-by: Vincent Guittot <vincent.guittot@linaro.org>
Cc: Dietmar Eggemann <dietmar.eggemann@arm.com>
Cc: Joel Fernandes <joelaf@google.com>
Cc: Juri Lelli <juri.lelli@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Morten Rasmussen <morten.rasmussen@arm.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Rafael J . Wysocki <rafael.j.wysocki@intel.com>
Cc: Steve Muckle <smuckle@google.com>
Fixes: 7f65ea42 ("sched/fair: Add util_est on top of PELT")
Link: http://lkml.kernel.org/r/20180524141023.13765-3-patrick.bellasi@arm.com


Signed-off-by: Ingo Molnar <mingo@kernel.org>

parent 8ecf04e1

kernel/sched/fair.c

+8 −1

Original line number	Diff line number	Diff line
		@@ -5385,6 +5385,14 @@ enqueue_task_fair(struct rq rq, struct task_struct p, int flags)
		struct cfs_rq *cfs_rq;
		struct sched_entity *se = &p->se;

		/*
		* The code below (indirectly) updates schedutil which looks at
		* the cfs_rq utilization to select a frequency.
		* Let's add the task's estimated utilization to the cfs_rq's
		* estimated utilization, before we update 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
		@@ -5426,7 +5434,6 @@ 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);
		}

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