timers: Reduce __run_timers() latency for empty list
upstream commit: d550e81dc0
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>
Reviewed-by: Josh Triplett <josh@joshtriplett.org>
Acked-by: Peter Zijlstra <peterz@infradead.org>
Reviewed-by: Oleg Nesterov <oleg@redhat.com>
Reviewed-by: Steven Rostedt <rostedt@goodmis.org>
Tested-by: Mike Galbraith <bitbucket@online.de>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
This commit is contained in:
parent
6b698aef1a
commit
4eb7482303
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@ -341,6 +341,20 @@ void set_timer_slack(struct timer_list *timer, int slack_hz)
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}
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}
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EXPORT_SYMBOL_GPL(set_timer_slack);
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EXPORT_SYMBOL_GPL(set_timer_slack);
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/*
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* If the list is empty, catch up ->timer_jiffies to the current time.
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* The caller must hold the tvec_base lock. Returns true if the list
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* was empty and therefore ->timer_jiffies was updated.
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*/
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static bool catchup_timer_jiffies(struct tvec_base *base)
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{
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if (!base->all_timers) {
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base->timer_jiffies = jiffies;
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return true;
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}
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return false;
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}
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static void
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static void
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__internal_add_timer(struct tvec_base *base, struct timer_list *timer)
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__internal_add_timer(struct tvec_base *base, struct timer_list *timer)
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{
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{
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@ -1203,6 +1217,10 @@ static inline void __run_timers(struct tvec_base *base)
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struct timer_list *timer;
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struct timer_list *timer;
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spin_lock_irq(&base->lock);
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spin_lock_irq(&base->lock);
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if (catchup_timer_jiffies(base)) {
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spin_unlock_irq(&base->lock);
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return;
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}
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while (time_after_eq(jiffies, base->timer_jiffies)) {
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while (time_after_eq(jiffies, base->timer_jiffies)) {
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struct list_head work_list;
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struct list_head work_list;
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struct list_head *head = &work_list;
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struct list_head *head = &work_list;
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