Re: constant_tsc and TSC unstable

[Patrick McHardy <kaber@trash.net>]

H. Peter Anvin wrote:
> Paul Rolland (ポール・ロラン) 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.

On my core2duo I noticed that the TSC of the second core doesn't
start counting until the CPU is activated. Since they're not
synchronized manually anymore this makes the TSC check fail.


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