linux-kernel - Re: [PATCH] sched: Optimize core cookie matching check

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Message-ID: <a3059d6c-9e3e-459d-aeb2-ec009c9ab06a@linux.ibm.com>
Date: Thu, 6 Nov 2025 15:57:59 +0530
From: Madadi Vineeth Reddy <vineethr@...ux.ibm.com>
To: Fernand Sieber <sieberf@...zon.com>
Cc: kprateek.nayak@....com, mingo@...hat.com, peterz@...radead.org,
        linux-kernel@...r.kernel.org, juri.lelli@...hat.com,
        vincent.guittot@...aro.org, dietmar.eggemann@....com,
        rostedt@...dmis.org, bsegall@...gle.com, mgorman@...e.de,
        bristot@...hat.com, vschneid@...hat.com, dwmw@...zon.co.uk,
        jschoenh@...zon.de, liuyuxua@...zon.com,
        Madadi Vineeth Reddy <vineethr@...ux.ibm.com>
Subject: Re: [PATCH] sched: Optimize core cookie matching check

Hi Fernand,

On 05/11/25 20:55, Fernand Sieber wrote:
> Early return true if the core cookie matches. This avoids the SMT mask
> loop to check for an idle core, which might be more expensive on wide
> platforms.
> 
> Signed-off-by: Fernand Sieber <sieberf@...zon.com>
> ---
>  kernel/sched/sched.h | 5 ++++-
>  1 file changed, 4 insertions(+), 1 deletion(-)
> 
> diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
> index adfb6e3409d7..381cd561e99b 100644
> --- a/kernel/sched/sched.h
> +++ b/kernel/sched/sched.h
> @@ -1432,6 +1432,9 @@ static inline bool sched_core_cookie_match(struct rq *rq, struct task_struct *p)
>  	if (!sched_core_enabled(rq))
>  		return true;
>  
> +	if (rq->core->core_cookie == p->core_cookie)
> +		return true;
> +
>  	for_each_cpu(cpu, cpu_smt_mask(cpu_of(rq))) {
>  		if (!available_idle_cpu(cpu)) {
>  			idle_core = false;
> @@ -1443,7 +1446,7 @@ static inline bool sched_core_cookie_match(struct rq *rq, struct task_struct *p)
>  	 * A CPU in an idle core is always the best choice for tasks with
>  	 * cookies.
>  	 */
> -	return idle_core || rq->core->core_cookie == p->core_cookie;
> +	return idle_core;
>  }

LGTM.
Reviewed-by: Madadi Vineeth Reddy <vineethr@...ux.ibm.com>

Thanks,
Madadi Vineeth Reddy

>  
>  static inline bool sched_group_cookie_match(struct rq *rq,