[ntp:questions] Timekeeping broken on Windows XP with multimedia timer enabled (-M option)

Martin Burnicki martin.burnicki at meinberg.de
Thu Jan 21 13:52:22 UTC 2010

David J Taylor wrote:
> Is:
>   Performance Counter Frequency: 3.580
> a guarantee that the TSC isn't being used?

AFAIK if the TSC is used then the clock frequency reported for QPC matches
the CPU's clock full clock frequency, and IIRC then according to some MS
docs the reported frequency does not even change when the CPU's clock is
decreased for power saving. IMO that also wouldn't make much sense.

>From what I've seen the reported QPC clock frequency depends on which timer
circuit is being used. Some months ago I've already posted what I had

But of course I can not *guarantee* this is always correct ;-)

In that article there are also some hints which Windows versions / service
packs use which timer to implement QPC. I've just reread that article and
found this perfectly matches what Alan has observed, i.e. Windows XP SP3
should use the PM timer even if no /usepmtimer flag has been added in
Windows' boot.ini.

Of course it does not explain the problems Alan is observing.


Martin Burnicki

Meinberg Funkuhren
Bad Pyrmont

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