Re: [PATCH 4/6 v3] sched/eevdf: Cancel slice protection if short slice task is eligible

[K Prateek Nayak <kprateek.nayak@amd.com>]

Hello Vincent,

On 6/24/2026 8:42 PM, Vincent Guittot wrote:
> @@ -9896,16 +9891,23 @@ static void wakeup_preempt_fair(struct rq *rq, struct task_struct *p, int wake_f
>  	if (!nse && cfs_rq->nr_queued)
>  		goto pick;
>  
> +	/*
> +	 * If @p is eligible but not the next task to run then cancel protection
> +	 * to prevent large scheduling latency
> +	 */
> +	if (preempt_action == PREEMPT_WAKEUP_SHORT && entity_eligible(cfs_rq, pse))
> +		goto preempt;

We handle "pse->slice < se->slice" case before "pse->sched_delayed" case
and jump to "pick", but pse can get dequeued as a part of
pick_next_entity() if it was delayed and picked.

I think we can reach here for PREEMPT_WAKEUP_SHORT after pse is
completely dequeued from cfs_rq. If p is a task on root cfs_rq, we could
have blocked the task entirely and ideally it shouldn't be referenced
here.

Since a wakeup of delayed entity / on delayed hierarchy will call
wakeup_preempt() anyways, I think we should return early if we should
directly jump to update if we see "pse->sched_delayed".

> +
>  	if (sched_feat(RUN_TO_PARITY))
>  		update_protect_slice(cfs_rq, se);
>  
>  	return;
>  
>  preempt:
> -	if (preempt_action == PREEMPT_WAKEUP_SHORT) {
> -		cancel_protect_slice(se);
> +	cancel_protect_slice(se);
> +
> +	if (preempt_action == PREEMPT_WAKEUP_SHORT && nse == pse)
>  		set_next_buddy(&p->se);
> -	}
>  
>  	resched_curr_lazy(rq);
>  }

-- 
Thanks and Regards,
Prateek