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

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Message-ID: <48503CA3.9060808@compro.net>
Date:	Wed, 11 Jun 2008 16:59:15 -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 16:37:38 -0400
>>> Mark 
>>>
>> Ok, what would one use besides the tsc to take a fast high-res time
>> stamp in a kernel module that could also be used in user land (same
>> time source) to for instance calculate  the the time between an event
>> in the kernel to an event in user land?
>>
>> do_gettimeofday / gettimeofday are not really acceptable.
> 
> 
> why not? both of these (they're teh same) are the best the kernel can
> do. If there was a better way to do it, gettimeofday() would use it.
> It's not even a system call if we can get away with it
> (although system calls are pretty cheap)
> 
> really, think about it. if there was a better way, gettimeofday() would
> use it.
> 
> 

The results of gettimeofday are worse that what you describe about the tsc.
NTP etc... and take considerably longer the a tsc read.

Mark
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