linux-kernel - Re: [PATCH v5 2/2] sched/fair: update scale invariance of PELT

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Date:   Wed, 31 Oct 2018 10:18:39 +0100
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>,
        Morten Rasmussen <Morten.Rasmussen@....com>,
        Patrick Bellasi <patrick.bellasi@....com>,
        Paul Turner <pjt@...gle.com>, Ben Segall <bsegall@...gle.com>,
        Thara Gopinath <thara.gopinath@...aro.org>,
        pkondeti@...eaurora.org
Subject: Re: [PATCH v5 2/2] sched/fair: update scale invariance of PELT

Hi Dietmar,

On Wed, 31 Oct 2018 at 08:20, Dietmar Eggemann <dietmar.eggemann@....com> wrote:
>
> On 10/26/18 6:11 PM, Vincent Guittot wrote:
>
> [...]
>
> >   static int select_idle_sibling(struct task_struct *p, int prev_cpu, int cpu);
> >   static unsigned long task_h_load(struct task_struct *p);
> > @@ -764,7 +763,7 @@ void post_init_entity_util_avg(struct sched_entity *se)
> >                        * such that the next switched_to_fair() has the
> >                        * expected state.
> >                        */
> > -                     se->avg.last_update_time = cfs_rq_clock_task(cfs_rq);
> > +                     se->avg.last_update_time = cfs_rq_clock_pelt(cfs_rq);
> >                       return;
> >               }
> >       }
>
> There is this 1/cpu scaling of se->avg.util_sum (running_sum) in
> update_tg_cfs_runnable() so it can be used to calculate
> se->avg.runnable_load_sum (runnable_sum). I guess with your approach
> this should be removed.

Yes good catch

>
> > @@ -3466,7 +3465,7 @@ static void detach_entity_load_avg(struct cfs_rq *cfs_rq, struct sched_entity *s
> >   /* Update task and its cfs_rq load average */
> >   static inline void update_load_avg(struct cfs_rq *cfs_rq, struct sched_entity *se, int flags)
> >   {
> > -     u64 now = cfs_rq_clock_task(cfs_rq);
> > +     u64 now = cfs_rq_clock_pelt(cfs_rq);
> >       struct rq *rq = rq_of(cfs_rq);
> >       int cpu = cpu_of(rq);
> >       int decayed;
> > @@ -6694,6 +6693,12 @@ done: __maybe_unused;
> >       if (new_tasks > 0)
> >               goto again;
> >
> > +     /*
> > +      * rq is about to be idle, check if we need to update the
> > +      * lost_idle_time of clock_pelt
> > +      */
> > +     update_idle_rq_clock_pelt(rq);
> > +
> >       return NULL;
> >   }
>
> [...]