linux-kernel - Re: [PATCH 2/3] sched/fair: util

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Date:   Fri, 11 May 2018 09:41:17 +0100
From:   Patrick Bellasi <patrick.bellasi@....com>
To:     Viresh Kumar <viresh.kumar@...aro.org>
Cc:     linux-kernel@...r.kernel.org, linux-pm@...r.kernel.org,
        Ingo Molnar <mingo@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        "Rafael J . Wysocki" <rafael.j.wysocki@...el.com>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        Dietmar Eggemann <dietmar.eggemann@....com>,
        Morten Rasmussen <morten.rasmussen@....com>,
        Juri Lelli <juri.lelli@...hat.com>,
        Joel Fernandes <joelaf@...gle.com>,
        Steve Muckle <smuckle@...gle.com>
Subject: Re: [PATCH 2/3] sched/fair: util_est: update before schedutil

On 11-May 11:14, Viresh Kumar wrote:
> 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@...aro.org>
> > Signed-off-by: Patrick Bellasi <patrick.bellasi@....com>
> > Cc: Ingo Molnar <mingo@...hat.com>
> > Cc: Peter Zijlstra <peterz@...radead.org>
> > Cc: Vincent Guittot <vincent.guittot@...aro.org>
> > Cc: linux-kernel@...r.kernel.org
> > Cc: linux-pm@...r.kernel.org
> > ---
> >  kernel/sched/fair.c | 4 +++-
> >  1 file changed, 3 insertions(+), 1 deletion(-)
> 
> Fixes and Stable ?

Good idea, will add them.

> > 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@...aro.org>
> 
> -- 
> viresh

-- 
#include <best/regards.h>

Patrick Bellasi