lkml.org 
[lkml]   [2014]   [Jan]   [15]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: [PATCH tip/core/timers 2/4] timers: Reduce __run_timers() latency for empty list
On 01/14, Paul E. McKenney wrote:
>
> The __run_timers() function currently steps through the list one jiffy at
> a time

And this is very suboptimal if jiffies - timer_jiffies is huge. Looks
like, we should rework base->tv* structures, or (perhaps) optimize
the "cascade" logic so that __run_timers() can increment timer_jiffies
and move all the expired timers into work_list at one step. And the
->next_timer logic is obviously very suboptimal.

But this is almost off-topic, I agree that in the short term these
changes make sense.

> +static bool catchup_timer_jiffies(struct tvec_base *base)
> +{
> +#ifdef CONFIG_NO_HZ_FULL
> + if (!base->all_timers) {
> + base->timer_jiffies = jiffies;
> + return 1;
> + }
> +#endif /* #ifdef CONFIG_NO_HZ_FULL */
> + return 0;
> +}
> +
> static void
> __internal_add_timer(struct tvec_base *base, struct timer_list *timer)
> {
> @@ -1150,6 +1161,10 @@ static inline void __run_timers(struct tvec_base *base)
> struct timer_list *timer;
>
> spin_lock_irq(&base->lock);
> + if (catchup_timer_jiffies(base)) {
> + spin_unlock_irq(&base->lock);
> + return;
> + }


This is really minor, but perhaps it would be better to modify
run_timer_softirq() to call catchup_timer_jiffies() lockless along
with another fast-path time_after_eq() check.

Better yet, it would be nice to avoid raise_softirq(TIMER_SOFTIRQ),
but this is not simple due to hrtimer_run_pending().

Oleg.



\
 
 \ /
  Last update: 2014-01-15 18:41    [W:0.388 / U:0.052 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site