Re: [PATCH 06/20 v3] sched/eevdf: Add min slice check when selecting CPU

[Peter Zijlstra]

On Sat, Nov 07, 2026 at 11:57:12AM +0300, Kayra Cizmeci wrote:

> (My editor got crazy, so I had to copy this diff :<)
> 
> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> index 262626455497..8b0dd858f332 100644
> --- a/kernel/sched/fair.c
> +++ b/kernel/sched/fair.c
> @@ -8876,10 +8876,8 @@ static inline int sched_balance_find_dst_cpu(struct sched_domain *sd, struct tas
>  
>  static inline bool choose_sched_slice_rq(struct rq *rq, struct task_struct *p)
>  {
> -	if (p->se.slice < get_rq_min_slice(rq))
> -		return true;
> -
> -	return false;
> +	return p->se.slice < get_rq_min_slice(rq) &&
> +		READ_ONCE(rq->curr)->sched_class == &fair_sched_class;
>  }

that wants to be rcu_dereference_all() or somesuch, rather than
READ_ONCE().

The think I noticed is that it will only select one slice_cpu; it will
not consider another once its has found one.

This means it picks the oldest option, rather than the most recent one.
And given this is all racy as heck, the most recent one might in fact be
the better choice. It will have had less time to go stale.