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

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Date:   Mon, 4 Jun 2018 09:14:55 +0200
From:   Vincent Guittot <vincent.guittot@...aro.org>
To:     Juri Lelli <juri.lelli@...hat.com>
Cc:     Joel Fernandes <joelaf@...gle.com>,
        Patrick Bellasi <patrick.bellasi@....com>,
        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 <joel@...lfernandes.org>,
        "Cc: Android Kernel" <kernel-team@...roid.com>,
        Alessio Balsini <alessio.balsini@...tannapisa.it>
Subject: Re: [PATCH v5 05/10] cpufreq/schedutil: get max utilization

On 4 June 2018 at 09:04, Juri Lelli <juri.lelli@...hat.com> wrote:
> Hi Vincent,
>
> On 04/06/18 08:41, Vincent Guittot wrote:
>> On 1 June 2018 at 19:45, Joel Fernandes <joelaf@...gle.com> wrote:
>> > On Fri, Jun 01, 2018 at 03:53:07PM +0200, Vincent Guittot wrote:
>
> [...]
>
>> > IMO I feel its overkill to account dl_avg when we already have DL's running
>> > bandwidth we can use. I understand it may be too instanenous, but perhaps we
>>
>> We keep using dl bandwidth which is quite correct for dl needs but
>> doesn't reflect how it has disturbed other classes
>>
>> > can fix CFS's problems within CFS itself and not have to do this kind of
>> > extra external accounting ?
>
> I would also keep accounting for waiting time due to higher prio classes
> all inside CFS. My impression, when discussing it with you on IRC, was
> that we should be able to do that by not decaying cfs.util_avg when CFS
> is preempted (creating a new signal for it). Is not this enough?

We don't just want to not decay a signal but increase the signal to
reflect the amount of preemption
Then, we can't do that in a current signal. So you would like to add
another metrics in cfs_rq ?
The place doesn't really matter to be honest in cfs_rq or in dl_rq but
you will not prevent to add call in dl class to start/stop the
accounting of the preemption

>
> I feel we should try to keep cross-class accounting/interaction at a
> minimum.

accounting for cross class preemption can't be done without
cross-class accounting

Regards,
Vincent

>
> Thanks,
>
> - Juri