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Date:   Tue, 7 Jun 2022 11:03:30 +0100
From:   Vincent Donnefort <vdonnefort@google.com>
To:     Vincent Guittot <vincent.guittot@linaro.org>
Cc:     Dietmar Eggemann <dietmar.eggemann@arm.com>, peterz@infradead.org,
        mingo@redhat.com, linux-kernel@vger.kernel.org,
        morten.rasmussen@arm.com, chris.redpath@arm.com,
        qperret@google.com, tao.zhou@linux.dev, kernel-team@android.com
Subject: Re: [PATCH v9 2/7] sched/fair: Decay task PELT values during wakeup
 migration
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References: <20220523155140.2878563-1-vdonnefort@google.com>
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 <72bd6945-c167-65ba-6f81-fad2768972dc@arm.com>
 <Yp3JZIokwFxT+X6M@google.com>
 <CAKfTPtD6TpaJoz37Xv2_1Cc8ij_XGFjDTwA+TvN3ddiASkYc4g@mail.gmail.com>
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[...]

> > >
> > > > 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".