Commit 16d937f8 authored Dec 16, 2013 by Paul E. McKenney

timers: Reduce future __run_timers() latency for newly emptied 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.
Therefore, if we just emptied the timer wheel, for example, by deleting
the last timer, 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 catches ->timer_jiffies
for 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>

parent d550e81d

kernel/timer.c

+2 −0

Original line number	Diff line number	Diff line
		@@ -688,6 +688,7 @@ detach_expired_timer(struct timer_list timer, struct tvec_base base)
		if (!tbase_get_deferrable(timer->base))
		base->active_timers--;
		base->all_timers--;
		(void)catchup_timer_jiffies(base);
		}

		static int detach_if_pending(struct timer_list timer, struct tvec_base base,
		@@ -703,6 +704,7 @@ static int detach_if_pending(struct timer_list timer, struct tvec_base base,
		base->next_timer = base->timer_jiffies;
		}
		base->all_timers--;
		(void)catchup_timer_jiffies(base);
		return 1;
		}

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