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    SubjectRe: constant_tsc and TSC unstable
    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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