linux-kernel - Re: [PATCH v5 05/10] cpufreq/schedutil: get max utilization

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Message-ID: <20180529094750.GC8985@localhost.localdomain>
Date:   Tue, 29 May 2018 11:47:50 +0200
From:   Juri Lelli <juri.lelli@...hat.com>
To:     Vincent Guittot <vincent.guittot@...aro.org>
Cc:     Joel Fernandes <joel@...lfernandes.org>,
        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>,
        Quentin Perret <quentin.perret@....com>,
        Luca Abeni <luca.abeni@...tannapisa.it>,
        Claudio Scordino <claudio@...dence.eu.com>,
        Joel Fernandes <joelaf@...gle.com>,
        Alessio Balsini <alessio.balsini@...tannapisa.it>
Subject: Re: [PATCH v5 05/10] cpufreq/schedutil: get max utilization

On 29/05/18 08:48, Vincent Guittot wrote:
> On 29 May 2018 at 08:31, Juri Lelli <juri.lelli@...hat.com> wrote:
> > On 28/05/18 22:08, Joel Fernandes wrote:
> >> On Mon, May 28, 2018 at 12:12:34PM +0200, Juri Lelli wrote:
> >> [..]
> >> > > +
> >> > > + util = max_t(unsigned long, util, READ_ONCE(rq->avg_dl.util_avg));
> >> > > +
> >> > > + return util;
> >> >
> >> > Anyway, just a quick thought. I guess we should experiment with this a
> >> > bit. Now, I don't unfortunately have a Arm platform at hand for testing.
> >> > Claudio, Luca (now Cc-ed), would you be able to fire some tests with
> >> > this change?
> >> >
> >> > Oh, adding Joel and Alessio as well that experimented with DEADLINE
> >> > lately.
> >>
> >> I also feel that for power reasons, dl.util_avg shouldn't drive the OPP
> >> beyond what the running bandwidth is, or atleast do that only if CFS tasks
> >> are running and being preempted as you/Vincent mentioned in one of the
> >> threads.
> >
> > It's however a bit awkward that we might be running at a higher OPP when
> > CFS tasks are running (even though they are of less priority). :/
> 
> Even if cfs task has lower priority that doesn't mean that we should
> not take their needs into account.
> In the same way, we run at max OPP as soon as a RT task is runnable

Sure. What I fear is a little CFS utilization generating spikes because
dl.util_avg became big when running DL tasks. Not sure that can happen
though because such DL tasks should be throttled anyway.