Re: [PATCH v3 tip/core/timers 0/5] Crude timer-wheel latency hacks

[Steven Rostedt <rostedt@goodmis.org>]

On Wed, 15 Jan 2014 20:02:03 -0800
"Paul E. McKenney" <paulmck@linux.vnet.ibm.com> wrote:

> 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.
> 

Although I think the "(void)" is ugly and uncalled for (there's lots of
functions that return a value in the kernel that don't have that). But,
it's not up to me to argue this.

For all 5 patches,

Reviewed-by: Steven Rostedt <rostedt@goodmis.org>

-- Steve