From 11cc374f4643b1be16deab571e034409c6ee7e66 Mon Sep 17 00:00:00 2001 From: Tejun Heo Date: Tue, 6 Aug 2024 09:40:10 -1000 Subject: [PATCH] sched_ext: Simplify scx_can_stop_tick() invocation in sched_can_stop_tick() The way sched_can_stop_tick() used scx_can_stop_tick() was rather confusing and the behavior wasn't ideal when SCX is enabled in partial mode. Simplify it so that: - scx_can_stop_tick() can say no if scx_enabled(). - CFS tests rq->cfs.nr_running > 1 instead of rq->nr_running. This is easier to follow and leads to the correct answer whether SCX is disabled, enabled in partial mode or all tasks are switched to SCX. Peter, note that this is a bit different from your suggestion where sched_can_stop_tick() unconditionally returns scx_can_stop_tick() iff scx_switched_all(). The problem is that in partial mode, tick can be stopped when there is only one SCX task even if the BPF scheduler didn't ask and isn't ready for it. Signed-off-by: Tejun Heo Suggested-by: Peter Zijlstra Acked-by: David Vernet --- kernel/sched/core.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) diff --git a/kernel/sched/core.c b/kernel/sched/core.c index ec67b30f87c4..38df84d5a9f6 100644 --- a/kernel/sched/core.c +++ b/kernel/sched/core.c @@ -1286,10 +1286,10 @@ bool sched_can_stop_tick(struct rq *rq) * left. For CFS, if there's more than one we need the tick for * involuntary preemption. For SCX, ask. */ - if (!scx_switched_all() && rq->nr_running > 1) + if (scx_enabled() && !scx_can_stop_tick(rq)) return false; - if (scx_enabled() && !scx_can_stop_tick(rq)) + if (rq->cfs.nr_running > 1) return false; /* -- 2.25.1