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SubjectRe: [PATCH] x86 (64): make calibrate_APIC_clock() smp-safe
Martin Wilck wrote:
> Hi Thomas and Peter, hi everyone,
>
> Asynchrounous events (e.g.SMIs) which occur during the APIC timer
> calibration can cause timer miscalibrations, sometimes by large amounts.
>
> This patch fixes this by two separate measures:
> a) make sure that no significant interruption occurs between APIC and
> TSC reads
> b) make sure that the measurement loop isn't significantly longer
> than originally intended.
>
> I am sorry, due to a misconfiguration of our SMTP server I need to send
> the patch as attachment.
>

The other thing we may want to consider is doing multiple runs of the
calibration loop. I suspect we'd get a more accurate result running,
say, 9 loops of the 1/9 the current duration and looking either for the
best result or the median (NOT the mean.)

-hpa



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