linux-kernel - Re: [PATCH 2/2] sched/fair: Update comments regarding last and skip buddy

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Message-ID: <244e174a-5449-4730-963e-424a5b3edc05@linux.ibm.com>
Date: Mon, 25 Nov 2024 15:30:56 +0530
From: Madadi Vineeth Reddy <vineethr@...ux.ibm.com>
To: Adam Li <adamli@...amperecomputing.com>, peterz@...radead.org,
        mingo@...hat.com, juri.lelli@...hat.com, vincent.guittot@...aro.org
Cc: dietmar.eggemann@....com, rostedt@...dmis.org, bsegall@...gle.com,
        mgorman@...e.de, vschneid@...hat.com, linux-kernel@...r.kernel.org,
        patches@...erecomputing.com, cl@...ux.com,
        Madadi Vineeth Reddy <vineethr@...ux.ibm.com>
Subject: Re: [PATCH 2/2] sched/fair: Update comments regarding last and skip
 buddy

Hi Adam Li,

On 25/11/24 07:42, Adam Li wrote:
> Commit 5e963f2bd465 ("sched/fair: Commit to EEVDF") removed the "last" and
> "skip" buddy. Update comments in pick_next_entity().
> 
> Signed-off-by: Adam Li <adamli@...amperecomputing.com>
> ---
>  kernel/sched/fair.c | 8 +-------
>  1 file changed, 1 insertion(+), 7 deletions(-)
> 
> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> index cd1188b7f3df..d8826a8e0c77 100644
> --- a/kernel/sched/fair.c
> +++ b/kernel/sched/fair.c
> @@ -5602,17 +5602,11 @@ set_next_entity(struct cfs_rq *cfs_rq, struct sched_entity *se)
>  
>  static int dequeue_entities(struct rq *rq, struct sched_entity *se, int flags);
>  
> -/*
> - * Pick the next process, keeping these things in mind, in this order:
> - * 1) keep things fair between processes/task groups
> - * 2) pick the "next" process, since someone really wants that to run
> - * 3) pick the "last" process, for cache locality
> - * 4) do not run the "skip" process, if something else is available
> - */
>  static struct sched_entity *
>  pick_next_entity(struct rq *rq, struct cfs_rq *cfs_rq)
>  {
>  	/*
> +	 * Pick the "next" buddy, since someone really wants that to run.
>  	 * Enabling NEXT_BUDDY will affect latency but not fairness.
>  	 */

Yes, the LAST_BUDDY and SKIP_BUDDY are obsolete now.

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

Thanks,
Madadi Vineeth Reddy

>  	if (sched_feat(NEXT_BUDDY) &&