linux-kernel - Re: [PATCH v2 3/6] cpufreq: schedutil: ensure max frequency while running RT/DL tasks

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Date:   Thu, 6 Jul 2017 22:26:36 -0700
From:   Joel Fernandes <joelaf@...gle.com>
To:     Patrick Bellasi <patrick.bellasi@....com>
Cc:     Viresh Kumar <viresh.kumar@...aro.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Linux PM <linux-pm@...r.kernel.org>,
        Ingo Molnar <mingo@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        "Rafael J . Wysocki" <rafael.j.wysocki@...el.com>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        Juri Lelli <juri.lelli@....com>,
        Andres Oportus <andresoportus@...gle.com>,
        Todd Kjos <tkjos@...roid.com>,
        Morten Rasmussen <morten.rasmussen@....com>,
        Dietmar Eggemann <dietmar.eggemann@....com>,
        Steve Muckle <smuckle.linux@...il.com>,
        Brendan Jackman <brendan.jackman@....com>
Subject: Re: [PATCH v2 3/6] cpufreq: schedutil: ensure max frequency while
 running RT/DL tasks

Hi,

On Wed, Jul 5, 2017 at 6:41 AM, Patrick Bellasi <patrick.bellasi@....com> wrote:
[..]
>
>> But what about clearing the sched-class's flag from .pick_next_task() callback
>> when they return NULL ?
>>
>> What about something like this instead (completely untested), with which we
>> don't need the 2/3 patch as well:
>
> Just had a fast check but I think something like that can work.
> We had an internal discussion with Brendan (in CC now) which had a
> similar proposal.
>
> Main counter arguments for me was:
> 1. we wanna to reduce the pollution of scheduling classes code with
>    schedutil specific code, unless strictly necessary
> 2. we never had a "clear bit" semantics for flags updates
>
> Thus this proposal seemed to me less of a discontinuity wrt the
> current interface. However, something similar to what you propose
> below should also work. Let's collect some more feedback...
>

I was going to say something similar. I feel its much cleaner if the
scheduler clears the flags that it set, thus taking "ownership" of the
flag. I feel that will avoid complication like this where the governor
has to peek into what's currently running and such (and also help with
the suggestion I made for patch 2/3.

Maybe the interface needs an extension for "clear flag" semantics?

thanks,

-Joel