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

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Date:   Tue, 29 May 2018 08:48:55 +0200
From:   Vincent Guittot <vincent.guittot@...aro.org>
To:     Juri Lelli <juri.lelli@...hat.com>
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 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

>
>> With our DL experiments, I didn't measure power but got it to a point where
>> the OPP is scaling correctly based on DL parameters. I think Alessio did
>> measure power at his setup but I can't recall now. Alessio?
>
> I see. Thanks.