Re: System clock frequency offset changes drastically across reboots

John Sigler
2007-08-03T07:48:28Z

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> 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.