[PATCH v2 tip/core/timers] Crude timer-wheel latency hacks

["Paul E. McKenney" <paulmck@linux.vnet.ibm.com>]

Hello!

The following three patches provide some crude timer-wheel latency
patches.  I understand that a more comprehensive solution is in progress,
but in the meantime, these patches work well in cases where a given
CPU has either zero or one timers pending, which is a common case for
NO_HZ_FULL kernels.  So, on the off-chance that this is helpful to
someone, the individual patches are as follows:

1.	Add ->all_timers field to tbase_vec to count all timers, not
	just the non-deferrable ones.

2.	Avoid jiffy-at-a-time stepping when the timer wheel is empty.

3.	Avoid jiffy-at-a-time stepping when the timer wheel transitions
	to empty.

4.	Avoid jiffy-at-a-time stepping after a timer is added to an
	initially empty timer wheel.

Differences from v1:

o	Fix an embarrassing bug located by Oleg Nesterov where the
	timer wheel could be judged to be empty even if it contained
	deferrable timers.

							Thanx, Paul

------------------------------------------------------------------------

 b/kernel/timer.c |   22 ++++++++++++++++++++++
 1 file changed, 22 insertions(+)