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    SubjectRe: Regression in 2.6.27 caused by commit bfc0f59

    On Mon, 1 Sep 2008, Larry Finger wrote:
    > TSC calibrated against PIT
    > Detected 428.823 MHz processor.

    Ok, Thomas, that means that the PIT is reliable (not surprising), and the
    PM_TIMER isn't (again, I'm not horribly surprised). And HPET isn't
    available, of course.

    The old x86-32 code never even bothered with the PM_TIMER for calibration.
    I don't understand why the x86-64 code bothers with it either. Why not
    just drop that whole broken thing, and just depend on the PIT if there is
    no HPET?

    I would also like to point out that the 32-bit code actually had a much
    nicer PIT setup, using the much better documented mach_prepare_counter()
    and mach_countup() helper functions. I'm unhappy to note that the new
    "common" code uses what appears to be the inferior code.

    Also, note that this is _not_ a new issue. See "verify_pmtmr_rate()" in
    drivers/clocksource/acpi_pm.c, along with all the code to check that the
    reads are stable in "init_acpi_pm_clocksource()".

    IOW, the PM_TIMER has been found to be broken before. Depending on it for
    calibration is broken.


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      Last update: 2008-09-01 20:45    [W:0.019 / U:11.012 seconds]
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