Re: constant_tsc and TSC unstable

From: H. Peter Anvin
Date: Thu Nov 29 2007 - 14:04:55 EST


Paul Rolland (ããããããã) wrote:
Hello,

I've a machine with a Core2Duo CPU. /proc/cpuinfo reports the flag
constant_tsc, but at boot time, I have the log :

...
Total of 2 processors activated (6919.15 BogoMIPS).
ENABLING IO-APIC IRQs
..TIMER: vector=0x31 apic1=0 pin1=2 apic2=-1 pin2=-1
checking TSC synchronization [CPU#0 -> CPU#1]:
Measured 3978592228 cycles TSC warp between CPUs, turning off TSC clock.
Marking TSC unstable due to: check_tsc_sync_source failed.
Brought up 2 CPUs
...

This machine is running 2.6.23.1-21.fc7. I know I should report to Fedora,
but I was wondering if this is a bug or a feature ;)


constant_tsc means the TSC doesn't change with CPU core frequency.

The problem you're having is that the TSCs of your two cores are completely different, over a second apart. This is a bug, unrelated to constant_tsc.

-hpa



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