Commit 0abec32a authored by Peter Zijlstra's avatar Peter Zijlstra
Browse files

sched/hrtick: Mark hrtick timer LAZY_REARM 



The hrtick timer is frequently rearmed before expiry and most of the time
the new expiry is past the armed one. As this happens on every context
switch it becomes expensive with scheduling heavy work loads especially in
virtual machines as the "hardware" reprogamming implies a VM exit.

hrtimer now provide a lazy rearm mode flag which skips the reprogamming if:

    1) The timer was the first expiring timer before the rearm

    2) The new expiry time is farther out than the armed time

This avoids a massive amount of reprogramming operations of the hrtick
timer for the price of eventually taking the alredy armed interrupt for
nothing.

Mark the hrtick timer accordingly.

Signed-off-by: default avatarPeter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: default avatarThomas Gleixner <tglx@kernel.org>
Signed-off-by: default avatarPeter Zijlstra (Intel) <peterz@infradead.org>
Link: https://patch.msgid.link/20260224163429.475409346@kernel.org
parent b7dd6477

kernel/sched/core.c

+2 −1
Original line number Diff line number Diff line
@@ -998,7 +998,8 @@ static void hrtick_rq_init(struct rq *rq) 
{

	INIT_CSD(&rq->hrtick_csd, __hrtick_start, rq);

	rq->hrtick_sched = HRTICK_SCHED_NONE;

	hrtimer_setup(&rq->hrtick_timer, hrtick, CLOCK_MONOTONIC, HRTIMER_MODE_REL_HARD);

	hrtimer_setup(&rq->hrtick_timer, hrtick, CLOCK_MONOTONIC,

		      HRTIMER_MODE_REL_HARD | HRTIMER_MODE_LAZY_REARM);

}

#else /* !CONFIG_SCHED_HRTICK: */

static inline void hrtick_clear(struct rq *rq) { }