linux-kernel - Re: [PATCH v3 1/2] sched/cpufreq: always consider blocked FAIR utilization

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Date:   Thu, 31 May 2018 12:46:55 +0200
From:   "Rafael J. Wysocki" <rjw@...ysocki.net>
To:     Patrick Bellasi <patrick.bellasi@....com>
Cc:     "Rafael J. Wysocki" <rafael@...nel.org>,
        Linux Kernel Mailing List <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>,
        Viresh Kumar <viresh.kumar@...aro.org>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        Dietmar Eggemann <dietmar.eggemann@....com>,
        Morten Rasmussen <morten.rasmussen@....com>,
        Juri Lelli <juri.lelli@...hat.com>,
        Joel Fernandes <joelaf@...gle.com>,
        Steve Muckle <smuckle@...gle.com>
Subject: Re: [PATCH v3 1/2] sched/cpufreq: always consider blocked FAIR utilization

On Wednesday, May 30, 2018 6:50:10 PM CEST Patrick Bellasi wrote:
> On 27-May 11:50, Rafael J. Wysocki wrote:
> > On Thu, May 24, 2018 at 4:10 PM, Patrick Bellasi
> > <patrick.bellasi@....com> wrote:
> > > Since the refactoring introduced by:
> > >
> > >    commit 8f111bc357aa ("cpufreq/schedutil: Rewrite CPUFREQ_RT support")
> > >
> > > we aggregate FAIR utilization only if this class has runnable tasks.
> > > This was mainly due to avoid the risk to stay on an high frequency just
> > > because of the blocked utilization of a CPU not being properly decayed
> > > while the CPU was idle.
> > >
> > > However, since:
> > >
> > >    commit 31e77c93e432 ("sched/fair: Update blocked load when newly idle")
> > >
> > > the FAIR blocked utilization is properly decayed also for IDLE CPUs.
> > >
> > > This allows us to use the FAIR blocked utilization as a safe mechanism
> > > to gracefully reduce the frequency only if no FAIR tasks show up on a
> > > CPU for a reasonable period of time.
> > >
> > > Moreover, we also reduce the frequency drops of CPUs running periodic
> > > tasks which, depending on the task periodicity and the time required
> > > for a frequency switch, was increasing the chances to introduce some
> > > undesirable performance variations.
> > >
> > > Reported-by: Vincent Guittot <vincent.guittot@...aro.org>
> > > Signed-off-by: Patrick Bellasi <patrick.bellasi@....com>
> > > Acked-by: Viresh Kumar <viresh.kumar@...aro.org>
> > > Acked-by: Vincent Guittot <vincent.guittot@...aro.org>
> > > Tested-by: Vincent Guittot <vincent.guittot@...aro.org>
> > > Cc: Ingo Molnar <mingo@...hat.com>
> > > Cc: Peter Zijlstra <peterz@...radead.org>
> > > Cc: Rafael J. Wysocki <rafael.j.wysocki@...el.com>
> > > Cc: Vincent Guittot <vincent.guittot@...aro.org>
> > > Cc: Viresh Kumar <viresh.kumar@...aro.org>
> > > Cc: Joel Fernandes <joelaf@...gle.com>
> > > Cc: linux-kernel@...r.kernel.org
> > > Cc: linux-pm@...r.kernel.org
> > 
> > Reviewed-by: Rafael J. Wysocki <rafael.j.wysocki@...el.com>
> > 
> > Or please let me know if you want me to apply this one.
> 
> Hi Rafael, seems this patch has already been applied in tip/sched/core.
> However is missing your tag above. :/

That's OK.

I just wanted to let people know my opinion. :-)