Date: Mon, 22 Jun 2009 17:05:53 +0200
From: Ingo Molnar <mingo@elte.hu>
To: Martin Schwidefsky <schwidefsky@de.ibm.com>
Cc: Thomas Gleixner <tglx@linutronix.de>, linux-kernel@vger.kernel.org,
       Rob van der Heij <rvdheij@gmail.com>,
       Heiko Carstens <heiko.carstens@de.ibm.com>,
       john stultz <johnstul@us.ibm.com>, Andi Kleen <andi@firstfloor.org>,
       Peter Zijlstra <a.p.zijlstra@chello.nl>
Subject: Re: [patch 0/2] NOHZ vs. profile/oprofile v2
Message-ID: <20090622150553.GA14363@elte.hu>
References: <20090603152223.083010123@de.ibm.com> <alpine.LFD.2.00.0906092252150.3351@localhost.localdomain> <20090622162631.4b4dcee4@skybase> <20090622144110.GA9771@elte.hu> <20090622165936.0bb776e1@skybase>
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* Martin Schwidefsky <schwidefsky@de.ibm.com> wrote:

> On Mon, 22 Jun 2009 16:41:10 +0200
> Ingo Molnar <mingo@elte.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.

	Ingo
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