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

[Viresh Kumar]

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@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(-)

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@xxxxxxxxxx>

-- 
viresh