linux-kernel - Re: [PATCH v6 04/11] cpufreq/schedutil: use rt utilization tracking

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Date:   Mon, 18 Jun 2018 14:58:26 +0200
From:   Vincent Guittot <vincent.guittot@...aro.org>
To:     Dietmar Eggemann <dietmar.eggemann@....com>
Cc:     Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...nel.org>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        "Rafael J. Wysocki" <rjw@...ysocki.net>,
        Juri Lelli <juri.lelli@...hat.com>,
        Morten Rasmussen <Morten.Rasmussen@....com>,
        viresh kumar <viresh.kumar@...aro.org>,
        Valentin Schneider <valentin.schneider@....com>,
        Patrick Bellasi <patrick.bellasi@....com>,
        Joel Fernandes <joel@...lfernandes.org>,
        Daniel Lezcano <daniel.lezcano@...aro.org>,
        Quentin Perret <quentin.perret@....com>,
        Ingo Molnar <mingo@...hat.com>
Subject: Re: [PATCH v6 04/11] cpufreq/schedutil: use rt utilization tracking

On Mon, 18 Jun 2018 at 11:00, Dietmar Eggemann <dietmar.eggemann@....com> wrote:
>
> On 06/08/2018 02:09 PM, Vincent Guittot wrote:
> > Take into account rt utilization when selecting an OPP for cfs tasks in order
> > to reflect the utilization of the CPU.
>
> The rt utilization signal is only tracked per-cpu, not per-entity. So it
> is not aware of PELT migrations (attach/detach).
>
> IMHO, this patch deserves some explanation why the temporary
> inflation/deflation of the OPP driving utilization signal in case an
> rt-task migrates off/on (missing detach/attach for rt-signal) doesn't
> harm performance or energy consumption.
>
> There was some talk (mainly on #sched irc) about ... (1) preempted cfs
> tasks (with reduced demand (utilization id only running) signals) using
> this remaining rt utilization of an rt task which migrated off and ...
> (2) going to max when an rt tasks runs ... but a summary of all of that
> in this patch would really help to understand.

Ok. I will add more comments in the next version. I just wait a bit to
let time to get more feedback before sending a new release

>
> > Cc: Ingo Molnar <mingo@...hat.com>
> > Cc: Peter Zijlstra <peterz@...radead.org>
> > Signed-off-by: Vincent Guittot <vincent.guittot@...aro.org>
> > ---
> >   kernel/sched/cpufreq_schedutil.c | 9 ++++++++-
> >   1 file changed, 8 insertions(+), 1 deletion(-)
> >
> > diff --git a/kernel/sched/cpufreq_schedutil.c b/kernel/sched/cpufreq_schedutil.c
> > index 28592b6..32f97fb 100644
> > --- a/kernel/sched/cpufreq_schedutil.c
> > +++ b/kernel/sched/cpufreq_schedutil.c
> > @@ -56,6 +56,7 @@ struct sugov_cpu {
> >       /* The fields below are only needed when sharing a policy: */
> >       unsigned long           util_cfs;
> >       unsigned long           util_dl;
> > +     unsigned long           util_rt;
> >       unsigned long           max;
> >
> >       /* The field below is for single-CPU policies only: */
> > @@ -178,15 +179,21 @@ static void sugov_get_util(struct sugov_cpu *sg_cpu)
> >       sg_cpu->max = arch_scale_cpu_capacity(NULL, sg_cpu->cpu);
> >       sg_cpu->util_cfs = cpu_util_cfs(rq);
> >       sg_cpu->util_dl  = cpu_util_dl(rq);
> > +     sg_cpu->util_rt  = cpu_util_rt(rq);
> >   }
> >
> >   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)
> >               return sg_cpu->max;
> >
> > +     util = sg_cpu->util_dl;
> > +     util += sg_cpu->util_cfs;
> > +     util += sg_cpu->util_rt;
> > +
> >       /*
> >        * Utilization required by DEADLINE must always be granted while, for
> >        * FAIR, we use blocked utilization of IDLE CPUs as a mechanism to
> > @@ -197,7 +204,7 @@ static unsigned long sugov_aggregate_util(struct sugov_cpu *sg_cpu)
> >        * 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(sg_cpu->max, (sg_cpu->util_dl + sg_cpu->util_cfs));
> > +     return min(sg_cpu->max, util);
> >   }
> >
> >   static void sugov_set_iowait_boost(struct sugov_cpu *sg_cpu, u64 time, unsigned int flags)
> >
>