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    SubjectRe: Regression in 2.6.27 caused by commit bfc0f59
    On Tue, 2 Sep 2008, Linus Torvalds wrote:
    > You're definitely right that this could easily be the _real_ problem.
    > Especially as your TSC min value of 2160 is (a) pretty close to the
    > expected time of a microsecond and (b) so stable that I actually do not
    > believe that the PIT itself is at all emulated or the problem.

    On that box, the PIT is probably real hardware or a damned good
    emulation. When you look at the 10 loop values you see that it does
    50% perfectly fine calibration loops. The others are just SMI
    interruptions caused by random unknown crap in the BIOS.

    > Btw - as to caring about the average value: that's pointless. If you only
    > look at the average time the PIT read takes place, then it is going to
    > approximate that "pit_count" thing in the end that I already did.
    > Why? Because the average value should essentially end up being "(end_tsc -
    > start_tsc) / pit_count". And if you just compare that to "min_tsc", then
    > that should always be about a microsecond (on normal machines where the
    > PIT is essentially on the old emulated internal "ISA" bus on the
    > southbridge). So you end up with what I already posted, and you already
    > dismissed.
    > So average TSC is not any more interesting than "pit_count".

    Yeah, you're right. Math is hard :)



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      Last update: 2008-09-02 23:15    [W:0.020 / U:134.192 seconds]
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