Messages in this thread | | | Date | Thu, 24 Jul 2008 09:31:48 -0400 | From | "H. Peter Anvin" <> | Subject | Re: [PATCH] x86 (64): make calibrate_APIC_clock() smp-safe |
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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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