linux-kernel - Re: [PATCH v2 1/3] sched/cpufreq: always consider blocked FAIR utilization

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Date:   Mon, 14 May 2018 17:48:12 +0100
From:   Patrick Bellasi <patrick.bellasi@....com>
To:     Vincent Guittot <vincent.guittot@...aro.org>
Cc:     linux-kernel <linux-kernel@...r.kernel.org>,
        "open list:THERMAL" <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>,
        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 v2 1/3] sched/cpufreq: always consider blocked FAIR
 utilization

On 14-May 11:16, Vincent Guittot wrote:
> Hi Patrick,

Hi Vincent,
 
> On 11 May 2018 at 15:15, 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>
> > 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
> 
> With this patch, I can't see the spurious OPP changes that I was seeing before

Cool thanks... regarding OPP updates I've added some more comments in
my reply to Joel's comments to my last patch of this series.

Would be nice if you can have a look... toward the end there are some
considerations about schedutil updates (indirectly) triggered by your
patches for blocked load updates on IDLE CPUs.

> FWIW
> Acked-by: Vincent Guittot <vincent.guittot@...aro.org>
> Tested-by: Vincent Guittot <vincent.guittot@...aro.org>

Thanks for testing, will add these to the next respin.

-- 
#include <best/regards.h>

Patrick Bellasi