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SubjectRe: [PATCH 2/3] sched/fair: util_est: update before schedutil
On 10-05-18, 16:05, Patrick Bellasi wrote:
> 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@linaro.org>
> Signed-off-by: Patrick Bellasi <patrick.bellasi@arm.com>
> Cc: Ingo Molnar <mingo@redhat.com>
> Cc: Peter Zijlstra <peterz@infradead.org>
> Cc: Vincent Guittot <vincent.guittot@linaro.org>
> Cc: linux-kernel@vger.kernel.org
> Cc: linux-pm@vger.kernel.org
> ---
> kernel/sched/fair.c | 4 +++-
> 1 file changed, 3 insertions(+), 1 deletion(-)

Fixes and Stable ?

> 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);
> }

Acked-by: Viresh Kumar <viresh.kumar@linaro.org>

--
viresh

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