Hello!
The following five 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.
Note that these patches do not help in the case where a given timer wheel
has a pair of widely separated timers, while the more comprehensive
solution is likely to handle more gracefully. 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.
5. Make internal_add_timer() update ->next_timer if ->active_timers == 0,
courtesy of Oleg Nesterov.
Differences from v2:
o Add patch #5 from Oleg.
o Move the check for adding to an empty timer wheel from mod_timer()
to internal_add_timer(), as suggested by Oleg Nesterov.
o Addressed review comments from Oleg, Steven Rostedt, Josh Triplett,
and Fengguang Wu.
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 | 30 ++++++++++++++++++++++++++++--
1 file changed, 28 insertions(+), 2 deletions(-)
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