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

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Date:   Wed, 12 Jul 2023 17:30:39 +0200
From:   Vincent Guittot <vincent.guittot@...aro.org>
To:     Qais Yousef <qyousef@...alina.io>
Cc:     mingo@...hat.com, peterz@...radead.org, juri.lelli@...hat.com,
        dietmar.eggemann@....com, rostedt@...dmis.org, bsegall@...gle.com,
        mgorman@...e.de, bristot@...hat.com, vschneid@...hat.com,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] sched/fair: remove util_est boosting

On Tue, 11 Jul 2023 at 17:47, Qais Yousef <qyousef@...alina.io> wrote:
>
> On 07/06/23 15:51, Vincent Guittot wrote:
> > There is no need to use runnable_avg when estimating util_est and that
> > even generates wrong behavior because one includes blocked tasks whereas
> > the other one doesn't. This can lead to accounting twice the waking task p,
> > once with the blocked runnable_avg and another one when adding its
> > util_est.
> >
> > cpu's runnable_avg is already used when computing util_avg which is then
> > compared with util_est.
> >
> > In some situation, feec will not select prev_cpu but another one on the
> > same performance domain because of higher max_util
> >
> > Fixes: 7d0583cf9ec7 ("sched/fair, cpufreq: Introduce 'runnable boosting'")
> > Signed-off-by: Vincent Guittot <vincent.guittot@...aro.org>
> > ---
>
> Can we verify the numbers that introduced this magic boost are still valid
> please?

TBH I don't expect it but I agree it's worth checking. Dietmar could
you rerun your tests with this change ?

>
> Otherwise LGTM.
>
>
> Thanks!
>
> --
>
> Qais Yousef
>
> >  kernel/sched/fair.c | 3 ---
> >  1 file changed, 3 deletions(-)
> >
> > diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> > index a80a73909dc2..77c9f5816c31 100644
> > --- a/kernel/sched/fair.c
> > +++ b/kernel/sched/fair.c
> > @@ -7289,9 +7289,6 @@ cpu_util(int cpu, struct task_struct *p, int dst_cpu, int boost)
> >
> >               util_est = READ_ONCE(cfs_rq->avg.util_est.enqueued);
> >
> > -             if (boost)
> > -                     util_est = max(util_est, runnable);
> > -
> >               /*
> >                * During wake-up @p isn't enqueued yet and doesn't contribute
> >                * to any cpu_rq(cpu)->cfs.avg.util_est.enqueued.
> > --
> > 2.34.1
> >