tree b811a626f38d2b27d57e67e769bdecdc736cfac9
parent 16d937f880312e3f47157d4d6d6ebf7e61523378
author Paul E. McKenney <paulmck@linux.vnet.ibm.com> 1387219310 -0800
committer Paul E. McKenney <paulmck@linux.vnet.ibm.com> 1393360740 -0800

timers: Reduce future __run_timers() latency for first add to 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.
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 <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>