linux-kernel - Re: PROBLEM: no cpu MHz in /proc/cpuinfo on 2.6.25.4-rt6

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Date:	Wed, 11 Jun 2008 14:28:40 -0700
From:	Arjan van de Ven <arjan@...radead.org>
To:	markh@...pro.net
Cc:	"linux-os (Dick Johnson)" <linux-os@...logic.com>,
	Jan Engelhardt <jengelh@...ozas.de>,
	"Kok, Auke" <auke-jan.h.kok@...el.com>,
	solsTiCe d'Hiver <solstice.dhiver@...il.com>,
	linux-kernel@...r.kernel.org
Subject: Re: PROBLEM: no cpu MHz in /proc/cpuinfo on 2.6.25.4-rt6

On Wed, 11 Jun 2008 17:08:09 -0400
Mark Hounschell <markh@...pro.net> wrote:

> > 
> > btw you also changed the problem from "what is the cpu frequency" to
> > "how usable is rdtsc for time". My entire point was that these
> > weren't related...
> > 
> > 
> 
> If they are not the same how do you know at what rate the tsc is
> counting.

it's not ticking at the cpu frequency as general rule.
For current cpus, your best bet is to calibrate against some external
time source... it'll stay constant after that, unless you go to idle,
then it may or may not stop (or both). For older cpus it'll change with
frequency changes.


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