linux-kernel - Re: [PATCH] sched/fair: Remove stale references to LAST_BUDDY and SKIP

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Message-ID: <4da6d43b-59f6-48e4-b58c-2f0792035851@linux.ibm.com>
Date: Sun, 13 Apr 2025 09:40:44 +0530
From: Madadi Vineeth Reddy <vineethr@...ux.ibm.com>
To: Peter Zijlstra <peterz@...radead.org>, Ingo Molnar <mingo@...hat.com>
Cc: Juri Lelli <juri.lelli@...hat.com>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        Dietmar Eggemann <dietmar.eggemann@....com>,
        Steven Rostedt <rostedt@...dmis.org>, Ben Segall <bsegall@...gle.com>,
        Mel Gorman <mgorman@...e.de>, Valentin Schneider <vschneid@...hat.com>,
        LKML <linux-kernel@...r.kernel.org>,
        Adam Li
 <adamli@...amperecomputing.com>,
        Madadi Vineeth Reddy <vineethr@...ux.ibm.com>
Subject: Re: [PATCH] sched/fair: Remove stale references to LAST_BUDDY and
 SKIP_BUDDY

Hi Peter, Ingo,

Ping.

Any thoughts on this? Can it be picked up?

Thanks,
Madadi Vineeth Reddy

On 14/03/25 14:31, Madadi Vineeth Reddy wrote:
> Commit 5e963f2bd465 ("sched/fair: Commit to EEVDF") removed the
> functionality associated with LAST_BUDDY and SKIP_BUDDY. However,
> some outdated references remained in the comments for pick_next_entity
> and check_preempt_wakeup_fair. This commit cleans up those comments
> to maintain clarity and correctness.
> 
> No functional change intended.
> 
> Co-developed-by: Adam Li <adamli@...amperecomputing.com>
> Signed-off-by: Adam Li <adamli@...amperecomputing.com>
> Signed-off-by: Madadi Vineeth Reddy <vineethr@...ux.ibm.com>
> ---
>  kernel/sched/fair.c | 6 +-----
>  1 file changed, 1 insertion(+), 5 deletions(-)
> 
> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> index 9dafb374d76d..379dbcbb24e9 100644
> --- a/kernel/sched/fair.c
> +++ b/kernel/sched/fair.c
> @@ -5578,8 +5578,6 @@ 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)
> @@ -8780,9 +8778,7 @@ static void check_preempt_wakeup_fair(struct rq *rq, struct task_struct *p, int
>  	 *
>  	 * Note: this also catches the edge-case of curr being in a throttled
>  	 * group (e.g. via set_curr_task), since update_curr() (in the
> -	 * enqueue of curr) will have resulted in resched being set.  This
> -	 * prevents us from potentially nominating it as a false LAST_BUDDY
> -	 * below.
> +	 * enqueue of curr) will have resulted in resched being set.
>  	 */
>  	if (test_tsk_need_resched(rq->curr))
>  		return;