System clock frequency offset changes drastically across reboots

John Sigler
2007-07-27T11:57:22Z

Hello everyone,

I'm using 2.6.20.7-rt8 on a P3.

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?

Regards.