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authorPaul E. McKenney <paulmck@linux.vnet.ibm.com>2013-12-16 05:57:10 -0800
committerPaul E. McKenney <paulmck@linux.vnet.ibm.com>2014-02-25 12:39:00 -0800
commitd550e81dc0ddc04f1b417c179c214103a28e0ee8 (patch)
treea873c6b1a980500c59af7b194374d604e3dba1eb /kernel/timer.c
parentfff421580f512fc044cc7421fdff31a7a6997350 (diff)
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.c18
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;