From b0a44fa5e2a22ff67752bbc08c651a2efac3e5fe Mon Sep 17 00:00:00 2001 From: Peter Zijlstra Date: Tue, 24 Feb 2026 17:38:12 +0100 Subject: [PATCH] sched/core: Prepare for deferred hrtimer rearming The hrtimer interrupt expires timers and at the end of the interrupt it rearms the clockevent device for the next expiring timer. That's obviously correct, but in the case that a expired timer sets NEED_RESCHED the return from interrupt ends up in schedule(). If HRTICK is enabled then schedule() will modify the hrtick timer, which causes another reprogramming of the hardware. That can be avoided by deferring the rearming to the return from interrupt path and if the return results in a immediate schedule() invocation then it can be deferred until the end of schedule(), which avoids multiple rearms and re-evaluation of the timer wheel. Add the rearm checks to the existing sched_hrtick_enter/exit() functions, which already handle the batched rearm of the hrtick timer. For now this is just placing empty stubs at the right places which are all optimized out by the compiler until the guard condition becomes true. Signed-off-by: Peter Zijlstra (Intel) Signed-off-by: Thomas Gleixner Signed-off-by: Peter Zijlstra (Intel) Link: https://patch.msgid.link/20260224163431.208580085@kernel.org --- kernel/sched/core.c | 6 ++++++ 1 file changed, 6 insertions(+) diff --git a/kernel/sched/core.c b/kernel/sched/core.c index 2d1239a8b2306..49a64b4117a13 100644 --- a/kernel/sched/core.c +++ b/kernel/sched/core.c @@ -876,6 +876,7 @@ enum { HRTICK_SCHED_NONE = 0, HRTICK_SCHED_DEFER = BIT(1), HRTICK_SCHED_START = BIT(2), + HRTICK_SCHED_REARM_HRTIMER = BIT(3) }; static void hrtick_clear(struct rq *rq) @@ -974,6 +975,8 @@ void hrtick_start(struct rq *rq, u64 delay) static inline void hrtick_schedule_enter(struct rq *rq) { rq->hrtick_sched = HRTICK_SCHED_DEFER; + if (hrtimer_test_and_clear_rearm_deferred()) + rq->hrtick_sched |= HRTICK_SCHED_REARM_HRTIMER; } static inline void hrtick_schedule_exit(struct rq *rq) @@ -991,6 +994,9 @@ static inline void hrtick_schedule_exit(struct rq *rq) hrtimer_cancel(&rq->hrtick_timer); } + if (rq->hrtick_sched & HRTICK_SCHED_REARM_HRTIMER) + __hrtimer_rearm_deferred(); + rq->hrtick_sched = HRTICK_SCHED_NONE; } -- 2.47.3