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From: Vincent Guittot <vincent.guittot@linaro.org>
Date: Thu, 30 Mar 2017 15:21:57 +0200
Message-ID: <CAKfTPtC+FdARdK=TO_i=k_UrnZviwUb8rm_=9OW8yCXLRixMBA@mail.gmail.com>
Subject: Re: [RFD PATCH 4/5] sched/cpufreq_schedutil: always consider all CPUs
 when deciding next freq
To: Juri Lelli <juri.lelli@arm.com>
Cc: "Rafael J. Wysocki" <rjw@rjwysocki.net>,
        Peter Zijlstra <peterz@infradead.org>,
        "mingo@redhat.com" <mingo@redhat.com>,
        viresh kumar <viresh.kumar@linaro.org>,
        linux-kernel <linux-kernel@vger.kernel.org>,
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        Thomas Gleixner <tglx@linutronix.de>,
        Steven Rostedt <rostedt@goodmis.org>,
        Luca Abeni <luca.abeni@santannapisa.it>, claudio@evidence.eu.com,
        Tommaso Cucinotta <tommaso.cucinotta@santannapisa.it>,
        bristot@redhat.com, Mathieu Poirier <mathieu.poirier@linaro.org>,
        Todd Kjos <tkjos@android.com>, Joel Fernandes <joelaf@google.com>,
        Andres Oportus <andresoportus@google.com>,
        Morten Rasmussen <morten.rasmussen@arm.com>,
        Dietmar Eggemann <dietmar.eggemann@arm.com>,
        Patrick Bellasi <patrick.bellasi@arm.com>,
        Ingo Molnar <mingo@kernel.org>
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On 30 March 2017 at 10:58, Juri Lelli <juri.lelli@arm.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