linux-kernel - Re: [PATCH v4] sched/freq: move call to cpufreq_update

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Message-ID: <CAKfTPtC3g4iCxvAJo9Km9fZ0fPSw5Jt9TY2+xF7kxGmOZ66gxw@mail.gmail.com>
Date:   Fri, 15 Nov 2019 12:03:31 +0100
From:   Vincent Guittot <vincent.guittot@...aro.org>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     linux-kernel <linux-kernel@...r.kernel.org>,
        Ingo Molnar <mingo@...hat.com>,
        Dietmar Eggemann <dietmar.eggemann@....com>,
        Juri Lelli <juri.lelli@...hat.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Mel Gorman <mgorman@...e.de>,
        Doug Smythies <dsmythies@...us.net>,
        "open list:THERMAL" <linux-pm@...r.kernel.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Sargun Dhillon <sargun@...gun.me>, Tejun Heo <tj@...nel.org>,
        Xie XiuQi <xiexiuqi@...wei.com>, xiezhipeng1@...wei.com,
        Srinivas Pandruvada <srinivas.pandruvada@...ux.intel.com>
Subject: Re: [PATCH v4] sched/freq: move call to cpufreq_update_util

On Fri, 15 Nov 2019 at 11:51, Peter Zijlstra <peterz@...radead.org> wrote:
>
> On Fri, Nov 15, 2019 at 11:46:01AM +0100, Vincent Guittot wrote:
> > On Fri, 15 Nov 2019 at 11:37, Peter Zijlstra <peterz@...radead.org> wrote:
>
> > > Sure, but then it can still remember the value passed in last and use
> > > that state later.
> > >
> > > It doesn't _have_ to completely discard values.
> >
> > yes but it means that we run at the "wrong" frequency during this
> > period and also that the cpufreq must in this case set a kind of timer
> > to resubmit a new frequency change out of scheduler event
>
> But if, as you say, we're completely shutting down the event stream
> when everything has decayed, that's still true, right?

But It doesn't because there is nothing else to do.

This patch does 2 things:
- fix the spurious call to cpufreq just before attaching a task
- make sure cpufreq is still called when cfs is 0 but not irq/rt or dl

There are somehow related but not fully