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

David J Taylor david-taylor at blueyonder.delete-this-bit.and-this-part.co.uk.invalid
Thu Jan 21 15:51:27 UTC 2010

"Martin Burnicki" <martin.burnicki at meinberg.de> wrote in message 
news:mp2m27-dp3.ln1 at gateway.py.meinberg.de...
> 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
> found:
> http://lists.ntp.org/pipermail/questions/2009-March/022159.html
> 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.
> Regards,
> Martin

Thanks, Martin.  I'm beginning to wish I'd never asked, as I have Windows 
XP SP3 here and yet the performance counter is running at 2.4GHz (Intel 
E6600 dual-core).  Or does the PM_Timer only apply to AMD systems?

The AMD Vista and Windows-7 desktop systems show 3.579...MHz, an Intel 
Windows-7 portable 1.757MHz (PIT?), an Intel Vista portable 14.3MHz 
(HPET), and an Intel Windows Vista Desktop 14.3MHz.

All frequencies you listed, and nothing which helps Alan.  Seemed to have 
a peculiar timer resolutions though - I never seen 3.906 ms or 1.953 ms. 
What software is setting those?


More information about the questions mailing list