From 15257cc2f905dbf5813c0bfdd3c15885f28093c4 Mon Sep 17 00:00:00 2001 From: Vincent Guittot Date: Fri, 23 Jan 2026 11:28:58 +0100 Subject: [PATCH] sched/fair: Revert force wakeup preemption This agressively bypasses run_to_parity and slice protection with the assumpiton that this is what waker wants but there is no garantee that the wakee will be the next to run. It is a better choice to use yield_to_task or WF_SYNC in such case. This increases the number of resched and preemption because a task becomes quickly "ineligible" when it runs; We update the task vruntime periodically and before the task exhausted its slice or at least quantum. Example: 2 tasks A and B wake up simultaneously with lag = 0. Both are eligible. Task A runs 1st and wakes up task C. Scheduler updates task A's vruntime which becomes greater than average runtime as all others have a lag == 0 and didn't run yet. Now task A is ineligible because it received more runtime than the other task but it has not yet exhausted its slice nor a min quantum. We force preemption, disable protection but Task B will run 1st not task C. Sidenote, DELAY_ZERO increases this effect by clearing positive lag at wake up. Fixes: e837456fdca8 ("sched/fair: Reimplement NEXT_BUDDY to align with EEVDF goals") Signed-off-by: Vincent Guittot Signed-off-by: Peter Zijlstra (Intel) Link: https://patch.msgid.link/20260123102858.52428-1-vincent.guittot@linaro.org --- kernel/sched/fair.c | 10 ---------- 1 file changed, 10 deletions(-) diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c index a148c61a8085..3eaeceda71b0 100644 --- a/kernel/sched/fair.c +++ b/kernel/sched/fair.c @@ -8828,16 +8828,6 @@ static void check_preempt_wakeup_fair(struct rq *rq, struct task_struct *p, int if ((wake_flags & WF_FORK) || pse->sched_delayed) return; - /* - * If @p potentially is completing work required by current then - * consider preemption. - * - * Reschedule if waker is no longer eligible. */ - if (in_task() && !entity_eligible(cfs_rq, se)) { - preempt_action = PREEMPT_WAKEUP_RESCHED; - goto preempt; - } - /* Prefer picking wakee soon if appropriate. */ if (sched_feat(NEXT_BUDDY) && set_preempt_buddy(cfs_rq, wake_flags, pse, se)) { -- 2.47.3