Re: [RFC PATCH 3/9] sched: add sched feature to disable idle core search

[Subhra Mazumdar]

On 9/5/19 3:17 AM, Patrick Bellasi wrote:
> On Fri, Aug 30, 2019 at 18:49:38 +0100, subhra mazumdar wrote...
>
> > Add a new sched feature SIS_CORE to have an option to disable idle core
> > search (select_idle_core).
> >
> > Signed-off-by: subhra mazumdar <subhra.mazumdar@xxxxxxxxxx>
> > ---
> >   kernel/sched/features.h | 1 +
> >   1 file changed, 1 insertion(+)
> >
> > diff --git a/kernel/sched/features.h b/kernel/sched/features.h
> > index 858589b..de4d506 100644
> > --- a/kernel/sched/features.h
> > +++ b/kernel/sched/features.h
> > @@ -57,6 +57,7 @@ SCHED_FEAT(TTWU_QUEUE, true)
> >    */
> >   SCHED_FEAT(SIS_AVG_CPU, false)
> >   SCHED_FEAT(SIS_PROP, true)
> > +SCHED_FEAT(SIS_CORE, true)
> Why do we need a sched_feature? If you think there are systems in
> which the usage of latency-nice does not make sense for in "Select Idle
> Sibling", then we should probably better add a new Kconfig option.
This is not for latency-nice but to be able to disable a different aspect
of the scheduler, i.e searching for idle cores. This can be made part of
latency-nice (i.e not do idle core search if latency-nice is below a
certain value) but even then having a feature to disable it doesn't hurt.
> If that's the case, you can probably use the init/Kconfig's
> "Scheduler features" section, recently added by:
>
>    commit 69842cba9ace ("sched/uclamp: Add CPU's clamp buckets refcounting")
>
> >   /*
> >    * Issue a WARN when we do multiple update_rq_clock() calls
> Best,
> Patrick