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Subject[PATCH RT 30/31] timers: Reduce future __run_timers() latency for first add to empty list
3.10.70-rt75-rc1 stable review patch.
If anyone has any objections, please let me know.


From: "Paul E. McKenney" <>

upstream commit: 18d8cb64c9c074cbe2bd677ab10fff8283abdb62

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.
Therefore, just before we add a timer to an empty timer wheel, we should
mark the timer wheel as being up to date. This marking will reduce (and
perhaps eliminate) the jiffy-stepping that a future __run_timers() call
will need to do in response to some future timer posting or migration.
This commit therefore updates ->timer_jiffies for this case.

Signed-off-by: Paul E. McKenney <>
Reviewed-by: Josh Triplett <>
Acked-by: Peter Zijlstra <>
Reviewed-by: Oleg Nesterov <>
Reviewed-by: Steven Rostedt <>
Tested-by: Mike Galbraith <>
Signed-off-by: Steven Rostedt <>
kernel/timer.c | 1 +
1 file changed, 1 insertion(+)

diff --git a/kernel/timer.c b/kernel/timer.c
index 39f5caef6714..06050920aee5 100644
--- a/kernel/timer.c
+++ b/kernel/timer.c
@@ -401,6 +401,7 @@ __internal_add_timer(struct tvec_base *base, struct timer_list *timer)

static void internal_add_timer(struct tvec_base *base, struct timer_list *timer)
+ (void)catchup_timer_jiffies(base);
__internal_add_timer(base, timer);
* Update base->active_timers and base->next_timer

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