Messages in this thread Patch in this message | | | From | "Paul E. McKenney" <> | Subject | [PATCH tip/core/timers 1/3] timers: Reduce __run_timers() latency for empty list | Date | Mon, 13 Jan 2014 20:15:17 -0800 |
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From: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
The __run_timers() function currently steps through the list one jiffy at a time in order to update the timer wheel. However, if the timer wheel is empty, no adjustment is needed other than updating ->timer_jiffies. In this case, which is likely to be common for NO_HZ_FULL kernels, the kernel currently incurs a large latency for no good reason. This commit therefore short-circuits this case.
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> --- kernel/timer.c | 15 +++++++++++++++ 1 file changed, 15 insertions(+)
diff --git a/kernel/timer.c b/kernel/timer.c index 6582b82fa966..21849275828f 100644 --- a/kernel/timer.c +++ b/kernel/timer.c @@ -337,6 +337,17 @@ void set_timer_slack(struct timer_list *timer, int slack_hz) } EXPORT_SYMBOL_GPL(set_timer_slack); +static bool catchup_timer_jiffies(struct tvec_base *base) +{ +#ifdef CONFIG_NO_HZ_FULL + if (!base->active_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) { @@ -1146,6 +1157,10 @@ 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; + } while (time_after_eq(jiffies, base->timer_jiffies)) { struct list_head work_list; struct list_head *head = &work_list; -- 1.8.1.5
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