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

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Date:	Tue, 10 Jun 2008 13:42:02 -0700
From:	"Kok, Auke" <auke-jan.h.kok@...el.com>
To:	Arjan van de Ven <arjan@...radead.org>
CC:	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 Tue, 10 Jun 2008 21:52:23 +0200
> solsTiCe d'Hiver <solstice.dhiver@...il.com> wrote:
> 
>> hi,
>>
>> i am running a 2.6.25.5-rt6 kernel.
>> i know there is no such thing as 2.6.25.5-rt6 yet. so i have checked
>> with a 2.6.25.4-rt6 kernel and i have the same issue.
>>
>> when i try to run jackd (0.109.2) i get that strange error:
>> FATAL: cannot locate cpu MHz in /proc/cpuinfo
>>
>> and it appears that /proc/cpuinfo lack the line 
>> cpu MHz:
> 
> 
> 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?

I just poked into Jackd and it seems to be using fallback code to calculate timing
intervals from the cpu MHz value (config/os/gnu-linux/time.c).

the code itself is self-addmittedly a kludge:


122 /*
123  * This is another kludge.  It looks CPU-dependent, but actually it
124  * reflects the lack of standards for the Linux kernel formatting of
125  * /proc/cpuinfo.
126  */
127
128 jack_time_t
129 jack_get_mhz (void)
130 {
131         FILE *f = fopen("/proc/cpuinfo", "r");

one kludge building on another :)


Auke

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