diff options
authorPaul E. McKenney <paulmck@linux.vnet.ibm.com>2013-12-16 05:57:10 -0800
committerAnders Roxell <anders.roxell@linaro.org>2015-06-01 12:03:38 +0200
commit5f906aa66682a41b1f0c1351b63be1019d05d9f6 (patch)
parent67343ee10dd14b2f21373f92317d81e285051c74 (diff)
timers: Reduce __run_timers() latency for empty list
upstream commit: d550e81dc0ddc04f1b417c179c214103a28e0ee8 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>
1 files changed, 18 insertions, 0 deletions
diff --git a/kernel/timer.c b/kernel/timer.c
index 251fdacfebdb..9cf70c562fac 100644
--- a/kernel/timer.c
+++ b/kernel/timer.c
@@ -341,6 +341,20 @@ void set_timer_slack(struct timer_list *timer, int slack_hz)
+ * 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)
@@ -1203,6 +1217,10 @@ static inline void __run_timers(struct tvec_base *base)
struct timer_list *timer;
+ 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;