linux-kernel - Re: [PATCH v9 2/7] sched/fair: Decay task PELT values during wakeup migration

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Date:   Tue, 7 Jun 2022 12:19:14 +0200
From:   Vincent Guittot <vincent.guittot@...aro.org>
To:     Vincent Donnefort <vdonnefort@...gle.com>
Cc:     Dietmar Eggemann <dietmar.eggemann@....com>, peterz@...radead.org,
        mingo@...hat.com, linux-kernel@...r.kernel.org,
        morten.rasmussen@....com, chris.redpath@....com,
        qperret@...gle.com, tao.zhou@...ux.dev, kernel-team@...roid.com
Subject: Re: [PATCH v9 2/7] sched/fair: Decay task PELT values during wakeup migration

On Tue, 7 Jun 2022 at 12:03, Vincent Donnefort <vdonnefort@...gle.com> wrote:
>
> [...]
>
> > > >
> > > > > diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
> > > > > index bf4a0ec98678..97bc26e5c8af 100644
> > > > > --- a/kernel/sched/sched.h
> > > > > +++ b/kernel/sched/sched.h
> > > > > @@ -648,6 +648,10 @@ struct cfs_rq {
> > > > >     int                     runtime_enabled;
> > > > >     s64                     runtime_remaining;
> > > > >
> > > > > +   u64                     throttled_pelt_idle;
> > > > > +#ifndef CONFIG_64BIT
> > > > > +   u64                     throttled_pelt_idle_copy;
> > > > > +#endif
> > > > >     u64                     throttled_clock;
> > > > >     u64                     throttled_clock_pelt;
> > > > >     u64                     throttled_clock_pelt_time;
> > > > > @@ -1020,6 +1024,12 @@ struct rq {
> > > > >     u64                     clock_task ____cacheline_aligned;
> > > > >     u64                     clock_pelt;
> > > > >     unsigned long           lost_idle_time;
> > > > > +   u64                     clock_pelt_idle;
> > > > > +   u64                     enter_idle;
> > > > > +#ifndef CONFIG_64BIT
> > > > > +   u64                     clock_pelt_idle_copy;
> > > > > +   u64                     enter_idle_copy;
> > > > > +#endif
> > > > >
> > > > >     atomic_t                nr_iowait;
> > > >
> > > > `throttled_pelt_idle`, `clock_pelt_idle` and `enter_idle` are clock
> > > > snapshots when cfs_rq resp. rq go idle. But the naming does not really
> > > > show this relation. And this makes reading those equations rather difficult.
> > > >
> > > > What about something like `throttled_clock_pelt_time_enter_idle`,
> > > > `clock_pelt_enter_idle`, `clock_enter_idle`? Especially the first one is
> > > > too long but something which shows that those are clock snapshots when
> > > > enter idle would IMHO augment readability in migrate_se_pelt_lag().
> > >
> > > What if I drop the "enter"?
> > >
> > >  clock_idle;
> > >  clock_pelt_idle;
> > >  throttled_clock_pelt_time_idle;
> >
> > and you can even remove the _time for throttled_clock_pelt_idle
> >
>
> Hum, "throttled_clock_pelt" already exists, while what we really snapshot is
> "throttled_clock_pelt_time".

What is snapshot is throttled_clock_pelt when entering idle so my
proposal of "throttled_clock_pelt_idle"
throttled_clock_pelt_idle doesn't exist and reflect  that it's
throttled_clock_pelt when cfs_rq enter idle just like clock_pelt_idle
reflect clock_pelt when entering idle