linux-kernel - Re: [PATCH 3/3] sched/fair: schedutil: explicit update only when required

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Message-ID: <20180515165304.GH12217@hirez.programming.kicks-ass.net>
Date:   Tue, 15 May 2018 18:53:04 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Patrick Bellasi <patrick.bellasi@....com>
Cc:     Vincent Guittot <vincent.guittot@...aro.org>,
        Joel Fernandes <joel@...lfernandes.org>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        "open list:THERMAL" <linux-pm@...r.kernel.org>,
        Ingo Molnar <mingo@...hat.com>,
        "Rafael J . Wysocki" <rafael.j.wysocki@...el.com>,
        Viresh Kumar <viresh.kumar@...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 3/3] sched/fair: schedutil: explicit update only when
 required

On Tue, May 15, 2018 at 03:53:43PM +0100, Patrick Bellasi wrote:
> On 15-May 12:19, Vincent Guittot wrote:
> > On 14 May 2018 at 18:32, Patrick Bellasi <patrick.bellasi@....com> wrote:

> > Yes se becomes NULL only when you reach root domain

root group; domains are something else again ;-)

> Thus, the scheduler knows that we are going to sleep: does is really
> makes sense to send a notification in this case?

It might; esp. on these very slow changing machines.

> What about adding a new explicit callback at the end of:
>    update_blocked_averages() ?
> 
> Something like:
> 
> ---8<---
> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> index cb77407ba485..6eb0f31c656d 100644
> --- a/kernel/sched/fair.c
> +++ b/kernel/sched/fair.c
> @@ -7740,6 +7740,9 @@ static void update_blocked_averages(int cpu)
>         if (done)
>                 rq->has_blocked_load = 0;
>  #endif
> +
> +       cpufreq_update_util(rq, SCHED_CPUFREQ_IDLE);
> +
>         rq_unlock_irqrestore(rq, &rf);
>  }
> ---8<---
> 
> Where we can also pass in a new SCHED_CPUFREQ_IDLE flag just to notify
> schedutil that the CPU is currently IDLE?
> 
> Could that work?

Simlarly you could add ENQUEUE/DEQUEUE flags I suppose. But let's do all
that later in separate patches and evaluate the impact separately, OK?