linux-kernel - Re: [RFD PATCH 4/5] sched/cpufreq_schedutil: always consider all CPUs when deciding next freq

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Message-ID: <CAKfTPtC+FdARdK=TO_i=k_UrnZviwUb8rm_=9OW8yCXLRixMBA@mail.gmail.com>
Date:   Thu, 30 Mar 2017 15:21:57 +0200
From:   Vincent Guittot <vincent.guittot@...aro.org>
To:     Juri Lelli <juri.lelli@....com>
Cc:     "Rafael J. Wysocki" <rjw@...ysocki.net>,
        Peter Zijlstra <peterz@...radead.org>,
        "mingo@...hat.com" <mingo@...hat.com>,
        viresh kumar <viresh.kumar@...aro.org>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        "linux-pm@...r.kernel.org" <linux-pm@...r.kernel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Steven Rostedt <rostedt@...dmis.org>,
        Luca Abeni <luca.abeni@...tannapisa.it>,
        claudio@...dence.eu.com,
        Tommaso Cucinotta <tommaso.cucinotta@...tannapisa.it>,
        bristot@...hat.com, Mathieu Poirier <mathieu.poirier@...aro.org>,
        Todd Kjos <tkjos@...roid.com>,
        Joel Fernandes <joelaf@...gle.com>,
        Andres Oportus <andresoportus@...gle.com>,
        Morten Rasmussen <morten.rasmussen@....com>,
        Dietmar Eggemann <dietmar.eggemann@....com>,
        Patrick Bellasi <patrick.bellasi@....com>,
        Ingo Molnar <mingo@...nel.org>
Subject: Re: [RFD PATCH 4/5] sched/cpufreq_schedutil: always consider all CPUs
 when deciding next freq

On 30 March 2017 at 10:58, Juri Lelli <juri.lelli@....com> wrote:
> Hi,
>
> On 30/03/17 00:41, Rafael J. Wysocki wrote:
>> On Friday, March 24, 2017 02:08:59 PM Juri Lelli wrote:
>> > No assumption can be made upon the rate at which frequency updates get
>> > triggered, as there are scheduling policies (like SCHED_DEADLINE) which
>> > don't trigger them so frequently.
>> >
>> > Remove such assumption from the code.
>>
>> But the util/max values for idle CPUs may be stale, no?
>>
>
> Right, that might be a problem. A proper solution I think would be to
> remotely update such values for idle CPUs, and I believe Vincent is
> working on a patch for that.

Yes. I'm working on a patch that will regularly update the blocked
load/utilization of idle CPU. This update will be done on a slow pace
to make sure that utilization and load will be decayed regularly

>
> As mid-term workarounds, changing a bit the current one, come to my
> mind:
>
>  - consider TICK_NSEC (continue) only when SCHED_CPUFREQ_DL is not set
>  - remove CFS contribution (without triggering a freq update) when a CPU
>    enters IDLE; this might not work well, though, as we probably want
>    to keep in blocked util contribution for a bit
>
> What you think is the way to go?
>
> Thanks,
>
> - Juri