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

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Message-ID: <20456740.6R3DDKEUDv@aspire.rjw.lan>
Date:   Sun, 17 Dec 2017 01:19:16 +0100
From:   "Rafael J. Wysocki" <rjw@...ysocki.net>
To:     Viresh Kumar <viresh.kumar@...aro.org>
Cc:     "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 Saturday, December 16, 2017 5:47:07 PM CET Viresh Kumar wrote:
> On 16 December 2017 at 22:10, Rafael J. Wysocki <rafael@...nel.org> wrote:
> > On Wed, Dec 13, 2017 at 10:53 AM, Viresh Kumar <viresh.kumar@...aro.org> wrote:
> 
> >> +#define SCHED_CPUFREQ_CLEAR    (1U << 31)
> >
> > I'm not thrilled by this, because schedutil is not the only user of
> > the flags and it's totally unclear what the other user(s) should do
> > when this is set.
> 
> intel-pstate is the only other user of the IOWAIT flag, right? In order
> not to change the current behavior, we can update that to return early
> for now ?

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?

Thanks,
Rafael