* [email protected] <[email protected]> wrote:
> Subject: i386/apic: Rework local apic timer calibration
> From: Thomas Gleixner <[email protected]>
>
> The local apic timer calibration has two problem cases:
>
> 1. The calibration is based on readout of the PIT/HPET timer to detect
> the wrap of the periodic tick. It happens that a box gets stuck in the
> calibration loop due to a PIT with a broken readout function.
>
> 2. CoreDuo boxen show a sporadic PIT runs too slow defect, which results
> in a wrong lapic calibration. The PIT goes back to normal operation once
> the lapic timer is switched to periodic mode.
>
> Rework the code to address both problems:
> - Make the calibration interrupt driven. This removes the wait_timer_tick
> magic hackery from lapic.c and time_hpet.c. The clockevents framework
> allows easy substitution of the global tick event handler for the
> calibration. This is more accurate than monitoring jiffies. At this
> point of the boot process, nothing disturbes the interrupt delivery, so
> the results are very accurate.
>
> - Verify the calibration against the PM timer, when available by using the
> early access function. When the measured calibration period is outside
> of an one percent window, then the lapic timer calibration is adjusted
> to the pm timer result.
>
> - Verify the calibration by running the lapic timer with the calibration
> handler. Disable lapic timer in case of deviation.
>
> This also removes the "synchronization" of the local apic timer to the
> global tick. This synchronization never worked, as there is no way to
> synchronize PIT(HPET) and local APIC timer. The synchronization by waiting
> for the tick just alignes the local APIC timer for the first events, but
> later the events drift away due to the different clocks. Removing the
> "sync" is just randomizing the asynchronous behaviour at setup time.
>
> Signed-off-by: Thomas Gleixner <[email protected]>
> Signed-off-by: Andrew Morton <[email protected]>
i agree with this method.
one question:
> + long tapic = apic_read(APIC_TMCCT);
> + unsigned long pm = acpi_pm_read_early();
is this function call safe if the box has no pm-timer?
otherwise, i have tested this on a couple of boxes, it looks good. This
patch should also solve some apic-calibration hangs reported against
Fedora.
Acked-by: Ingo Molnar <[email protected]>
Ingo
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