linux-kernel - Re: [patch 0/2] NOHZ vs. profile/oprofile v2

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Date:	Mon, 22 Jun 2009 17:18:34 +0200
From:	Martin Schwidefsky <schwidefsky@...ibm.com>
To:	Ingo Molnar <mingo@...e.hu>
Cc:	Thomas Gleixner <tglx@...utronix.de>, linux-kernel@...r.kernel.org,
	Rob van der Heij <rvdheij@...il.com>,
	Heiko Carstens <heiko.carstens@...ibm.com>,
	john stultz <johnstul@...ibm.com>,
	Andi Kleen <andi@...stfloor.org>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>
Subject: Re: [patch 0/2] NOHZ vs. profile/oprofile v2

On Mon, 22 Jun 2009 17:05:53 +0200
Ingo Molnar <mingo@...e.hu> wrote:

> 
> * Martin Schwidefsky <schwidefsky@...ibm.com> wrote:
> 
> > On Mon, 22 Jun 2009 16:41:10 +0200
> > Ingo Molnar <mingo@...e.hu> wrote:
> > 
> > > Hm, this is rather ugly. Why not use hrtimers like 'perf' does when 
> > > it fallback-samples based on the timer tick?
> > > 
> > > That method has three advantages:
> > > 
> > >  - no weird hookery needed
> > >  - resolution can go far beyond HZ
> > >  - it is evidently dynticks-safe
> > 
> > Hmm, if we replace the HZ based oprofile tick with an hrtimer we 
> > should add an interface to configure the sample interval as well, 
> > no? Otherwise we just replace one timer event (HZ) with another 
> > (hrtimer).
> 
> Even if the hrtimer is set with a 1/HZ period it's a better 
> solution, as it's dynticks safe without invasive changes.

Ok, but the patch will be quite big. All the profile_tick() calls from
the architecture files will have to be removed. And if we really want
to keep things separate there will be two sets of per-cpu hrtimer,
one for the old style profiler and one for oprofile. Any preference
for the user space interface to set the sample rate? A sysctl?

-- 
blue skies,
   Martin.

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

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