Re: [PATCH] i386: trust the PM-Timer calibration of the local APIC timer

Ingo Molnar
2007-03-17T07:23:56Z

* Thomas Gleixner <tglx@linutronix.de> wrote:

> When PM-Timer is available for local APIC timer calibration we can
> skip the verification of the calibrated time value. The resulting
> error is quite small on a bunch of evaluated platforms and is less
> harming than the observed false positives.
>
> We need to keep the verification on systems, which have no PM-Timer to
> avoid bogus local APIC timer calibrations in the range of factor 2-10,
> which can be observed when swicthing off the PM-timer support in the
> kernel configuration.
>
> The wrong calibration values are probably caused by SMM code trying to
> emulate a PS/2 keyboard from a (maybe connected or not) USB keyboard.
> This prohibits the accurate delivery of PIT interrupts, which are used
> to calibrate the local APIC timer. Unfortunately we have no way to
> disable this BIOS misfeature in the early boot process.
>
> Add also the dropped cpu_relax() back to the wait loops.
>
> Signed-off-by: Thomas Gleixner <tglx@linutronix.de>

Acked-by: Ingo Molnar <mingo@elte.hu>

Ingo