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

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Message-ID: <4850046C.4070602@compro.net>
Date:	Wed, 11 Jun 2008 12:59:24 -0400
From:	Mark Hounschell <markh@...pro.net>
To:	Arjan van de Ven <arjan@...radead.org>
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

Arjan van de Ven wrote:
> On Wed, 11 Jun 2008 10:14:50 -0400
> "linux-os (Dick Johnson)" <linux-os@...logic.com> wrote:
> 
>> I use CPU frequency to scale the output of rdtsc when timing
>> routines being optimized.
> 
> Ok this is broken in various really bad ways.
> 
> 1) CPU frequency is very fluctuating, it changes in principle every
> millisecond or more

I'm curious. What do you mean by "in principle"? And why will it change?

> 2) the rdtsc "frequency" is conceptually unrelated to cpu frequency. In
> fact, you'll be hard-pressed to buy a system today where this
> relationship works....
> 

And what do you mean by "conceptually unrelated to cpu frequency"?
Is it not the clock freq that is driving the cpu and the freq at which
the tsc is incremented?

> 
>> If CPU frequency goes away, I'll
>> have to add calibration routines to a lot of code. I don't
>> think one should just dispose of something that has been
>> useful for many years because they don't understand its
>> utility.
> 
> clearly you don't understand it either ;-)
> 

Could you explain what we don't understand about this please?

> I'm not arguing for removing it, at all. I'm just arguing that any user
> of it (being human or program) has some problems in how they use the
> data.
> 
> 
> 

Regards
Mark
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