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

* Thomas Gleixner <> 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 <>

Acked-by: Ingo Molnar <>

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