Re: [PATCH v2] sched/fair: Reschedule the cfs_rq when current is ineligible

[K Prateek Nayak]

Hello Chenyu,

Sorry, I'm a bit late to the thread but ...

On 6/13/2024 6:53 PM, Chen Yu wrote:
> [..snip..]
> > > I wonder if we can only take care of the NO_RUN_TO_PARITY case? Something like this,
> > >
> > > > diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> > > > index 03be0d1330a6..5e49a15bbdd3 100644
> > > > --- a/kernel/sched/fair.c
> > > > +++ b/kernel/sched/fair.c
> > > > @@ -745,6 +745,21 @@ int entity_eligible(struct cfs_rq *cfs_rq, struct sched_entity *se)
> > > >         return vruntime_eligible(cfs_rq, se->vruntime);
> > > > }
> > > >
> > > > +static bool check_entity_need_preempt(struct cfs_rq *cfs_rq, struct sched_entity *se)
> > > > +{
> > > if (sched_feat(RUN_TO_PARITY) || cfs_rq->nr_running <= 1 ||
> > >      !entity_eligible(cfs_rq, se))
> > > return false;
> > >
> > > return true;
> > >
> > > Thoughts?
> >
> > This does indeed look better. In that case, do I need to make the changes this way and send
> > out a version 3?
>
> If you mean the following changes, maybe we can continue the discussion here.
> This is just my 2 cents, not sure what others think of it. Anyway, I can launch some tests.
>
> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> index 8a5b1ae0aa55..c0fdb25f0695 100644
> --- a/kernel/sched/fair.c
> +++ b/kernel/sched/fair.c
> @@ -744,6 +744,15 @@ int entity_eligible(struct cfs_rq *cfs_rq, struct sched_entity *se)
>   	return vruntime_eligible(cfs_rq, se->vruntime);
>   }
>   
> +static bool check_curr_preempt(struct cfs_rq *cfs_rq, struct sched_entity *curr)
> +{
> +	if (sched_feat(RUN_TO_PARITY) || cfs_rq->nr_running <= 1 ||
> +	    !entity_eligible(cfs_rq, curr))

Shouldn't this return false if "entity_eligible(cfs_rq, curr)" returns 
true since curr is still vruntime eligible on cfs_rq?

Would it better to have check_curr_preempt() as follows:

	if (sched_feat(RUN_TO_PARITY) || cfs_rq->nr_running <= 1)
		return false;

	return entity_eligible(cfs_rq, curr);

which returns false if curr is ineligible and scheduler can go ahead and 
and call schedule to evaluate the next best step?

Please let me know if I'm missing something.

> +		return false;
> +
> +	return true;
> +}
> +
>   static u64 __update_min_vruntime(struct cfs_rq *cfs_rq, u64 vruntime)
>   {
>   	u64 min_vruntime = cfs_rq->min_vruntime;
> [..snip..]

--
Thanks and Regards,
Prateek