Re: [PATCH v2 1/6] sched/cache: Keep nr_pref_llc_running in the runnable domain

[Peter Zijlstra]

On Mon, Sep 21, 2026 at 05:37:22PM -0700, Tim Chen wrote:
> @@ -6395,15 +6429,27 @@ static __always_inline void return_cfs_rq_runtime(struct cfs_rq *cfs_rq);
>  
>  static void set_delayed(struct sched_entity *se)
>  {
> -	se->sched_delayed = 1;
> -
>  	/*
>  	 * Delayed se of cfs_rq have no tasks queued on them.
>  	 * Do not adjust h_nr_runnable since __dequeue_task()
>  	 * will account it for blocked tasks.
> +	 *
> +	 * This check can be removed because when flat pick
> +	 * patches get merged as only task can get delayed,
> +	 * same for clear_delayed().
>  	 */
> -	if (!entity_is_task(se))
> +	if (!entity_is_task(se)) {
> +		se->sched_delayed = 1;
>  		return;
> +	}

This is dead code. In Linus' tree, where this will be applied, this can
never happen. A possible backport of this fix however will need to take
care.

> +
> +	/*
> +	 * Drop a task leaving the runnable set.
> +	 * Needs to be called before sched_delayed is set.
> +	 * clear_delayed() mirrors this after clearing the flag.
> +	 */
> +	pref_llc_running_dec(rq_of(cfs_rq_of(se)), task_of(se));
> +	se->sched_delayed = 1;
>  
>  	for_each_sched_entity(se) {
>  		struct cfs_rq *cfs_rq = cfs_rq_of(se);