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 10:14:50 -0400
From:	"linux-os (Dick Johnson)" <linux-os@...logic.com>
To:	"Arjan van de Ven" <arjan@...radead.org>
Cc:	"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, Arjan van de Ven wrote:

> On Wed, 11 Jun 2008 15:52:57 +0200 (CEST)
> Jan Engelhardt <jengelh@...ozas.de> wrote:
>
>>
>> On Wednesday 2008-06-11 15:36, Arjan van de Ven wrote:
>>>>>> btw this is scary; the Mhz line in /proc/cpuinfo doesn't have
>>>>>> much meaning really, so applications using it and depending on
>>>>>> it is a rather big disaster ;-(
>>>>>>
>>>>>> Does anyone know why jackd wants to use this?
>>>>
>>>> It would be nice to have a /sys file where the CPU frequency is in,
>>>
>>> may I ask why? What would you do with it?
>>
>> Off the top off the head, just for reporting to the user. Desklets
>> and stuff.
>
> even then it doesn't mean much ;-(
>
>>> CPU frequency is...
>>> 1) not something that is fixed; it changes all the time
>>> 2) not a good indication for performance; remember the 3.4Ghz
>>> pentium4, a 2Ghz Core2Duo outperforms it
>>> 3) something which the cpu itself barely honors (the clock stops
>>> during idle etc etc)
>
>

I use CPU frequency to scale the output of rdtsc when timing
routines being optimized. 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. The fact that __some__ machines dynamically adjust
clock-speeds is not a valid reason to remove something useful
that impacts only boot time. Following this trend, soon there
won't be any floppy-drive code because "nobody" uses them
anymore. Please don't keep throwing good stuff away.

Cheers,
Dick Johnson
Penguin : Linux version 2.6.22.1 on an i686 machine (5588.29 BogoMips).
My book : http://www.AbominableFirebug.com/
_

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