From: "Paul E. McKenney" <paul...@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 <paul...@linux.vnet.ibm.com>
---
kernel/timer.c | 15 +++++++++++++++
1 file changed, 15 insertions(+)
diff --git a/kernel/timer.c b/kernel/timer.c
index 2245b7374c3d..295837e5e011 100644
--- a/kernel/timer.c
+++ b/kernel/timer.c
@@ -338,6 +338,17 @@ 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->all_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)
{
@@ -1150,6 +1161,10 @@ 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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