linux-kernel - Re: [PATCH v6 06/11] cpufreq/schedutil: use dl utilization tracking

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Date:   Fri, 8 Jun 2018 14:54:48 +0200
From:   Juri Lelli <juri.lelli@...hat.com>
To:     Vincent Guittot <vincent.guittot@...aro.org>
Cc:     Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...nel.org>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        "Rafael J. Wysocki" <rjw@...ysocki.net>,
        Dietmar Eggemann <dietmar.eggemann@....com>,
        Morten Rasmussen <Morten.Rasmussen@....com>,
        viresh kumar <viresh.kumar@...aro.org>,
        Valentin Schneider <valentin.schneider@....com>,
        Patrick Bellasi <patrick.bellasi@....com>,
        Joel Fernandes <joel@...lfernandes.org>,
        Daniel Lezcano <daniel.lezcano@...aro.org>,
        Quentin Perret <quentin.perret@....com>,
        Ingo Molnar <mingo@...hat.com>
Subject: Re: [PATCH v6 06/11] cpufreq/schedutil: use dl utilization tracking

On 08/06/18 14:48, Vincent Guittot wrote:
> On 8 June 2018 at 14:39, Juri Lelli <juri.lelli@...hat.com> wrote:
> > Hi Vincent,
> >
> > On 08/06/18 14:09, Vincent Guittot wrote:
> >> Now that we have both the dl class bandwidth requirement and the dl class
> >> utilization, we can detect when CPU is fully used so we should run at max.
> >> Otherwise, we keep using the dl bandwidth requirement to define the
> >> utilization of the CPU
> >>
> >> Cc: Ingo Molnar <mingo@...hat.com>
> >> Cc: Peter Zijlstra <peterz@...radead.org>
> >> Signed-off-by: Vincent Guittot <vincent.guittot@...aro.org>
> >> ---
> >
> > [...]
> >
> >> @@ -190,20 +192,24 @@ static unsigned long sugov_aggregate_util(struct sugov_cpu *sg_cpu)
> >>       if (rq->rt.rt_nr_running)
> >>               return sg_cpu->max;
> >>
> >> -     util = sg_cpu->util_dl;
> >> -     util += sg_cpu->util_cfs;
> >> +     util = sg_cpu->util_cfs;
> >>       util += sg_cpu->util_rt;
> >>
> >> +     if ((util + sg_cpu->util_dl) >= sg_cpu->max)
> >> +             return sg_cpu->max;
> >> +
> >
> > Mmm, won't we run at max (or reach max) with a, say, 100ms/500ms DL task
> > running alone?
> 
> not for a 100ms running task. You have to run more than 320ms to reach max value
> 
> 100ms/500ms will vary between 0 and 907

OK, right, my point I guess is still that such a task will run fine at
~250 and it might be save more energy by doing so?

Also, less freq switches (consider for example a few background CFS
tasks waking up from time to time).