Re: [RFC][PATCH] cache __next_timer_interrupt result

[Martin Schwidefsky <schwidefsky@de.ibm.com>]

On Wed, 22 Jul 2009 16:38:18 +0200 (CEST)
Thomas Gleixner <tglx@linutronix.de> wrote:

> On Tue, 21 Jul 2009, Martin Schwidefsky wrote:
> 
> > From: Martin Schwidefsky <schwidefsky@de.ibm.com>
> > 
> > Each time a cpu goes to sleep on a NOHZ=y system the timer wheel is
> > searched for the next timer interrupt. It can take quite a few cycles
> > to find the next pending timer. This patch adds a field to tvec_base
> > that caches the result of __next_timer_interrupt. The hit ratio is
> > around 80% on my thinkpad under normal use, on a server I've seen
> 
> Nice, I like it.

Thanks :-)
 
> > hit ratios from 5% to 95% dependent on the workload.
> 
> Which workloads result in lower hit ratios ? Heavy networking ?

5% ping-pong packet over loopback between two cpus. So yes, networking.

-- 
blue skies,
   Martin.

"Reality continues to ruin my life." - Calvin.