Message-ID: <43946ACE.9040405@argo.co.il>
Date: Mon, 05 Dec 2005 18:29:02 +0200
From: Avi Kivity <avi@argo.co.il>
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To: Dave Jones <davej@redhat.com>
CC: Lee Revell <rlrevell@joe-job.com>, Andi Kleen <ak@suse.de>,
       Venkatesh Pallipadi <venkatesh.pallipadi@intel.com>,
       Andrew Morton <akpm@osdl.org>, cpufreq <cpufreq@www.linux.org.uk>,
       linux-kernel <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH] CPU frequency display in /proc/cpuinfo
References: <20051202181927.GD9766@wotan.suse.de> <20051202104320.A5234@unix-os.sc.intel.com> <20051204164335.GB32492@isilmar.linta.de> <20051204183239.GE14247@wotan.suse.de> <1133725767.19768.12.camel@mindpipe> <20051205011611.GA12664@redhat.com>
In-Reply-To: <20051205011611.GA12664@redhat.com>
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Dave Jones wrote:

>I can't think of a single valid reason why a program would want
>to know the MHz rating of a CPU. Given that it's a) approximate,
>b) subject to change due to power management, c) completely nonsensical
>across CPU vendors, and d) only one of many variables regarding CPU
>performance, any program that bases any decision on the values found
>by parsing that field of /proc/cpuinfo is utterly broken beyond belief.
>  
>
Sometimes you need extremely low overhead time measurements, which need 
not be too accurate. One way to do this is to dump rdtsc measurements 
into some array, and later scale it using the cpu frequency.

I've done exactly this. The processes were pinned to their processors, 
and there was no frequency scaling in effect. It worked very well.
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