Message-ID: <46B2DD85.2030100@free.fr>
Date: Fri, 03 Aug 2007 09:47:17 +0200
From: John Sigler <linux.kernel@free.fr>
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CC: linux-rt-users@vger.kernel.org, johnstul@us.ibm.com, tglx@linutronix.de,
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Subject: Re: System clock frequency offset changes drastically across reboots
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[ Expanding recipients list to include NTP mailing list ]

> John Sigler wrote:
> 
>> I'm using 2.6.20.7-rt8 on a P3.
> 
> (But some ntpd users have reported the problem with mainline kernels and 
> different versions.)
> 
>> I've noticed that the frequency offset of my system clock (computed 
>> either by ntpd, or by hand) changes drastically across reboots.
>>
>> By drastically, I mean +/- 60 ppm every time I reboot.
>>
>> Apparently this is caused by some imprecision in the frequency 
>> estimation done in calculate_cpu_khz() (arch/i386/kernel/tsc.c)
>>
>> My brutally crude work-around was to skip the computation altogether 
>> and hard-code the "correct" value for cpu_khz.
>>
>> http://linux.kernel.free.fr/cpu_khz.adlink
>>
>> Has this issue been investigated more thoroughly by other users?

Is there, perhaps, more appropriate a forum to discuss such matters?

Regards.

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