Date: Wed, 22 Jul 2009 18:02:48 +0200
From: Martin Schwidefsky <schwidefsky@de.ibm.com>
To: Thomas Gleixner <tglx@linutronix.de>
Cc: linux-kernel@vger.kernel.org, Ingo Molnar <mingo@elte.hu>,
       john stultz <johnstul@us.ibm.com>,
       Venki Pallipadi <venkatesh.pallipadi@intel.com>
Subject: Re: [RFC][PATCH] cache __next_timer_interrupt result
Message-ID: <20090722180248.57e31f20@skybase>
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	<alpine.LFD.2.00.0907221632090.2813@localhost.localdomain>
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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.

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