linux-kernel - Re: [PATCH 2/7] Simple Performance Counters: x86

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Message-ID: <Pine.LNX.4.64.0708011144450.22867@schroedinger.engr.sgi.com>
Date:	Wed, 1 Aug 2007 11:45:39 -0700 (PDT)
From:	Christoph Lameter <clameter@....com>
To:	Andi Kleen <andi@...stfloor.org>
cc:	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/7] Simple Performance Counters: x86_64 support

On Wed, 1 Aug 2007, Andi Kleen wrote:

> > It is certainly interesting to compare alternative ways of handling the 
> > instruction streams by various processors or models of processors.
> 
> Well you have to do a lot more work then to handle instable TSCs then.

I have been using this for 2 years. It works fine for my purposes.

> In particular the frequencies can be different between CPUs, they 
> change (which you can catch with cpufreq notifiers) and during the
> cpufreq change period they're instable (as in you can't tell for
> some time which frequency they're currently running at and they
> might be running immediate frequencies) 

Well then simply make sure that they do not change while you measure.
 
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