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    SubjectRe: [PATCH] x86 (64): make calibrate_APIC_clock() SMI-safe (take 2)
    [Martin Wilck - Fri, Jul 25, 2008 at 03:38:47PM +0200]
    > I wrote:
    >
    >> I have to say that my simplified patch failed to do the calibration
    >> correctly on our test system (the original patch worked well). Please
    >> stay tuned, we are investigating this currently.
    >
    > Please forget that. It was observed on an old "enterprise" kernel with
    > which we are currently testing the backported patch with, and it was due
    > to the fact that the initial counter value on that kernel was divided by
    > APIC_DIVISOR (=16). The resulting initial counter value was too low in a
    > "SMI flood" case, the counter could overlap. APIC_DIVISOR is no longer
    > used in the current kernel.
    >
    > Martin
    >
    > --

    Martin, if I understood you right - this means your patch is not
    needed? Actually on 64bit mode APIC_DIVISOR is a bit hidden in
    __setup_APIC_LVTT - you may see it as APIC_TDR_DIV_16 while setting
    up divisor register. I was proposing patch for that but it leaded
    to potetntial overflow (thanks Ingo for catching) so we leave it as
    is. Maybe I miss something?

    - Cyrill -


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