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

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Date:   Fri, 8 Jun 2018 15:36:30 +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>,
        Luca Abeni <luca.abeni@...tannapisa.it>,
        Claudio Scordino <claudio@...dence.eu.com>
Subject: Re: [PATCH v6 06/11] cpufreq/schedutil: use dl utilization tracking

On 08/06/18 14:54, Juri Lelli wrote:
> 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?

As discussed on IRC, we still endup selecting 1/5 of max freq because
util_dl is below max.

So, turning point is at ~320ms/[something_bigger], which looks a pretty
big runtime, but I'm not sure if having that is OK. Also, it becomes
smaller with CFS/RT background "perturbations". Mmm.

BTW, adding Luca and Claudio. :)