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

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Message-ID: <20180530165010.GK30654@e110439-lin>
Date:   Wed, 30 May 2018 17:50:10 +0100
From:   Patrick Bellasi <patrick.bellasi@....com>
To:     "Rafael J. Wysocki" <rafael@...nel.org>
Cc:     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 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. :/

Dunno if I have / I can to do something about that.

> > ---
> > Changes in v3:
> >  - add "Tested-by" and "Acked-by" Vincent tags
> >
> > Changes in v2:
> >  - add "Acked-by" Viresh tag
> > ---
> >  kernel/sched/cpufreq_schedutil.c | 17 ++++++++---------
> >  1 file changed, 8 insertions(+), 9 deletions(-)
> >
> > diff --git a/kernel/sched/cpufreq_schedutil.c b/kernel/sched/cpufreq_schedutil.c
> > index e13df951aca7..28592b62b1d5 100644
> > --- a/kernel/sched/cpufreq_schedutil.c
> > +++ b/kernel/sched/cpufreq_schedutil.c
> > @@ -183,22 +183,21 @@ static void sugov_get_util(struct sugov_cpu *sg_cpu)
> >  static unsigned long sugov_aggregate_util(struct sugov_cpu *sg_cpu)
> >  {
> >         struct rq *rq = cpu_rq(sg_cpu->cpu);
> > -       unsigned long util;
> >
> > -       if (rq->rt.rt_nr_running) {
> > -               util = sg_cpu->max;
> > -       } else {
> > -               util = sg_cpu->util_dl;
> > -               if (rq->cfs.h_nr_running)
> > -                       util += sg_cpu->util_cfs;
> > -       }
> > +       if (rq->rt.rt_nr_running)
> > +               return sg_cpu->max;
> >
> >         /*
> > +        * Utilization required by DEADLINE must always be granted while, for
> > +        * FAIR, we use blocked utilization of IDLE CPUs as a mechanism to
> > +        * gracefully reduce the frequency when no tasks show up for longer
> > +        * periods of time.
> > +        *
> >          * Ideally we would like to set util_dl as min/guaranteed freq and
> >          * util_cfs + util_dl as requested freq. However, cpufreq is not yet
> >          * ready for such an interface. So, we only do the latter for now.
> >          */
> > -       return min(util, sg_cpu->max);
> > +       return min(sg_cpu->max, (sg_cpu->util_dl + sg_cpu->util_cfs));
> >  }
> >
> >  static void sugov_set_iowait_boost(struct sugov_cpu *sg_cpu, u64 time, unsigned int flags)
> > --
> > 2.15.1
> >

-- 
#include <best/regards.h>

Patrick Bellasi