linux-kernel - Re: [PATCH 2/4] sched: cpufreq: Keep track of cpufreq utilization update flags

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Date:   Mon, 18 Dec 2017 12:35:33 +0100
From:   "Rafael J. Wysocki" <rafael@...nel.org>
To:     Viresh Kumar <viresh.kumar@...aro.org>
Cc:     "Rafael J. Wysocki" <rjw@...ysocki.net>,
        "Rafael J. Wysocki" <rafael@...nel.org>,
        Ingo Molnar <mingo@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Linux PM <linux-pm@...r.kernel.org>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        Dietmar Eggemann <dietmar.eggemann@....com>,
        Morten Rasmussen <morten.rasmussen@....com>,
        Juri Lelli <juri.lelli@...hat.com>,
        Todd Kjos <tkjos@...roid.com>,
        Joel Fernandes <joelaf@...gle.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 2/4] sched: cpufreq: Keep track of cpufreq utilization
 update flags

On Mon, Dec 18, 2017 at 5:59 AM, Viresh Kumar <viresh.kumar@...aro.org> wrote:
> On 17-12-17, 01:19, Rafael J. Wysocki wrote:
>> We can do that in principle, but why should it return early?  Maybe it's
>> a good time to update things, incidentally?
>>
>> I actually don't like the SCHED_CPUFRREQ_CLEAR flag *concept* as it is very
>> much specific to schedutil and blatantly ignores everybody else.
>>
>> Alternatively, you could add two flags for clearing SCHED_CPUFREQ_RT and
>> SCHED_CPUFREQ_DL that could just be ingored entirely by intel_pstate.
>>
>> So, why don't you make SCHED_CPUFREQ_RT and SCHED_CPUFREQ_DL "sticky" until,
>> say, SCHED_CPUFREQ_NO_RT and SCHED_CPUFREQ_NO_DL are passed, respectively?
>
> I didn't like adding scheduling class specific flags, and wanted the code to
> treat all of them in the same way. And then the governors can make a policy over
> that, on what to ignore and what not to. For example with the current patchset,
> the governors can know when nothing else is queued on a CPU and CPU is going to
> get into idle loop. They can choose to (or not to) do something in that case.

Well, if SCHED_CPUFRREQ_CLEAR means "this CPU is going to enter the
idle loop" really, then it is better to call it
SCHED_CPUFRREQ_ENTER_IDLE, for example.

SCHED_CPUFRREQ_CLEAR meaning basically "you should clear these flags
now" doesn't seem to convey any information to whoever doesn't
squirrel the flags in the first place.