Re: [PATCH] sched/core: keep offline cpus out of core-wide selections

[Peter Zijlstra]

On Sun, Nov 01, 2026 at 10:12:18PM +0000, Ahmed Abdelraoof wrote:

>  kernel/sched/core.c       | 12 ++++++++++++
>  kernel/sched/core_sched.c |  2 +-
>  2 files changed, 13 insertions(+), 1 deletion(-)
> 
> diff --git a/kernel/sched/core.c b/kernel/sched/core.c
> index d7c3b43158de..f55f6a0befcc 100644
> --- a/kernel/sched/core.c
> +++ b/kernel/sched/core.c
> @@ -6413,6 +6413,9 @@ pick_next_task(struct rq *rq, struct rq_flags *rf)
>  	 */
>  	max = NULL;
>  	for_each_cpu_wrap(i, smt_mask, cpu) {
> +		if (!cpu_online(i))
> +			continue;
> +
>  		rq_i = cpu_rq(i);
>  
>  		/*
> @@ -6448,6 +6451,8 @@ pick_next_task(struct rq *rq, struct rq_flags *rf)
>  	for_each_cpu(i, smt_mask) {
>  		rq_i = cpu_rq(i);
>  		p = rq_i->core_pick;
> +		if (!p)
> +			continue;

Can't you do what you do in the last hunk for all 3 cases? It seems
unfortunate to have 3 different ways to iterate in one patch.

>  
>  		if (!cookie_equals(p, cookie)) {
>  			p = NULL;
> @@ -6760,6 +6765,13 @@ static inline void sched_core_cpu_dying(unsigned int cpu)
>  
>  	if (rq->core != rq)
>  		rq->core = rq;
> +
> +	/*
> +	 * Core-wide selections skip offline siblings and rely on a NULL
> +	 * core_pick to tell them apart from participants.
> +	 */
> +	rq->core_pick = NULL;
> +	rq->core_dl_server = NULL;
>  }
>  
>  #else /* !CONFIG_SCHED_CORE: */
> diff --git a/kernel/sched/core_sched.c b/kernel/sched/core_sched.c
> index 43e0bde3038e..1efde88da76e 100644
> --- a/kernel/sched/core_sched.c
> +++ b/kernel/sched/core_sched.c
> @@ -273,7 +273,7 @@ void __sched_core_account_forceidle(struct rq *rq)
>  		delta = div_u64(delta, rq->core->core_forceidle_occupation);
>  	}
>  
> -	for_each_cpu(i, smt_mask) {
> +	for_each_cpu_and(i, smt_mask, cpu_online_mask) {
>  		rq_i = cpu_rq(i);
>  		p = rq_i->core_pick ?: rq_i->curr;
>  
> -- 
> 2.47.3
>