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author | Paul E. McKenney <paulmck@linux.vnet.ibm.com> | 2013-12-16 05:57:10 -0800 |
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committer | Paul E. McKenney <paulmck@linux.vnet.ibm.com> | 2014-02-25 12:39:00 -0800 |
commit | d550e81dc0ddc04f1b417c179c214103a28e0ee8 (patch) | |
tree | a873c6b1a980500c59af7b194374d604e3dba1eb /kernel/timer.c | |
parent | fff421580f512fc044cc7421fdff31a7a6997350 (diff) | |
download | linux-stable-d550e81dc0ddc04f1b417c179c214103a28e0ee8.tar.gz linux-stable-d550e81dc0ddc04f1b417c179c214103a28e0ee8.tar.bz2 linux-stable-d550e81dc0ddc04f1b417c179c214103a28e0ee8.zip |
timers: Reduce __run_timers() latency for empty list
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>
Diffstat (limited to 'kernel/timer.c')
-rw-r--r-- | kernel/timer.c | 18 |
1 files changed, 18 insertions, 0 deletions
diff --git a/kernel/timer.c b/kernel/timer.c index fdc43834f3af..c8bc7091d8f3 100644 --- a/kernel/timer.c +++ b/kernel/timer.c @@ -338,6 +338,20 @@ void set_timer_slack(struct timer_list *timer, int slack_hz) } EXPORT_SYMBOL_GPL(set_timer_slack); +/* + * If the list is empty, catch up ->timer_jiffies to the current time. + * The caller must hold the tvec_base lock. Returns true if the list + * was empty and therefore ->timer_jiffies was updated. + */ +static bool catchup_timer_jiffies(struct tvec_base *base) +{ + if (!base->all_timers) { + base->timer_jiffies = jiffies; + return true; + } + return false; +} + static void __internal_add_timer(struct tvec_base *base, struct timer_list *timer) { @@ -1150,6 +1164,10 @@ 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; |