Re: [PATCH 1/6 v3] sched/fair: Set next buddy for preempt short

[K Prateek Nayak <kprateek.nayak@amd.com>]

Hello Vincent,

On 6/24/2026 8:42 PM, Vincent Guittot wrote:
> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> index d78467ec6ee1..83bce5a04f3d 100644
> --- a/kernel/sched/fair.c
> +++ b/kernel/sched/fair.c
> @@ -9903,7 +9903,7 @@ static void wakeup_preempt_fair(struct rq *rq, struct task_struct *p, int wake_f
>  preempt:
>  	if (preempt_action == PREEMPT_WAKEUP_SHORT) {
>  		cancel_protect_slice(se);
> -		clear_buddies(cfs_rq, se);
> +		set_next_buddy(&p->se);
>  	}

On a tangential note, I just noticed set_preempt_buddy() has two unused
parameters. Seems to have been like that since it was introduced in
commit e837456fdca8 ("sched/fair: Reimplement NEXT_BUDDY to align with
EEVDF goals"). 

Perhaps this can be included in the series too as a cleanup:

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 7c541f27a1ed..34b3888c4ccf 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -9755,9 +9755,7 @@ enum preempt_wakeup_action {
 	PREEMPT_WAKEUP_RESCHED,	/* Force reschedule. */
 };
 
-static inline bool
-set_preempt_buddy(struct cfs_rq *cfs_rq, int wake_flags,
-		  struct sched_entity *pse, struct sched_entity *se)
+static inline bool set_preempt_buddy(struct cfs_rq *cfs_rq, struct sched_entity *pse)
 {
 	/*
 	 * Keep existing buddy if the deadline is sooner than pse.
@@ -9903,9 +9901,7 @@ static void wakeup_preempt_fair(struct rq *rq, struct task_struct *p, int wake_f
 		goto update;
 
 	/* Prefer picking wakee soon if appropriate. */
-	if (sched_feat(NEXT_BUDDY) &&
-	    set_preempt_buddy(cfs_rq, wake_flags, pse, se)) {
-
+	if (sched_feat(NEXT_BUDDY) && set_preempt_buddy(cfs_rq, pse)) {
 		/*
 		 * Decide whether to obey WF_SYNC hint for a new buddy. Old
 		 * buddies are ignored as they may not be relevant to the
-- 
Thanks and Regards,
Prateek