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SubjectRe: [PATCH] timer: Lazily wakup nohz CPU when adding new timer.
On Mon, 28 Sep 2015, Yunhong Jiang wrote:
> static void internal_add_timer(struct tvec_base *base, struct timer_list *timer)
> {
> + bool kick_nohz = false;
> +
> /* Advance base->jiffies, if the base is empty */
> if (!base->all_timers++)
> base->timer_jiffies = jiffies;
> @@ -424,9 +426,17 @@ static void internal_add_timer(struct tvec_base *base, struct timer_list *timer)
> */
> if (!(timer->flags & TIMER_DEFERRABLE)) {
> if (!base->active_timers++ ||
> - time_before(timer->expires, base->next_timer))
> + time_before(timer->expires, base->next_timer)) {
> base->next_timer = timer->expires;
> - }
> + /*
> + * CPU in dynticks need reevaluate the timer wheel
> + * if newer timer added with next_timer updated.
> + */
> + if (base->nohz_active)
> + kick_nohz = true;
> + }
> + } else if (base->nohz_active && tick_nohz_full_cpu(base->cpu))
> + kick_nohz = true;

Why do you want to kick the other cpu when a deferrable timer got added?

Thanks,

tglx


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