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

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Message-ID: <CAJZ5v0jyHkVg80Uk5rh4Ax1wqFk=i+nbYEUfakDNrhu8zLnRzg@mail.gmail.com>
Date:   Thu, 30 Mar 2017 22:13:50 +0200
From:   "Rafael J. Wysocki" <rafael@...nel.org>
To:     Juri Lelli <juri.lelli@....com>
Cc:     "Rafael J. Wysocki" <rjw@...ysocki.net>,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>,
        Viresh Kumar <viresh.kumar@...aro.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Linux PM <linux-pm@...r.kernel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        Steven Rostedt <rostedt@...dmis.org>,
        Luca Abeni <luca.abeni@...tannapisa.it>,
        claudio@...dence.eu.com, tommaso.cucinotta@...tannapisa.it,
        bristot@...hat.com, 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 Thu, Mar 30, 2017 at 10:58 AM, Juri Lelli <juri.lelli@....com> wrote:
> Hi,

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.
>
> 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?

Well, do we want SCHED_DEADLINE util contribution to be there even for
idle CPUs?

Thanks,
Rafael