[ntp:questions] Re: Windows timekeeping - sudden degradation - why?

Martin Burnicki martin.burnicki at meinberg.de
Wed Dec 7 19:51:08 UTC 2005


David J Taylor wrote:
> Thanks for the response.  Yes, there was something about SP2 which fixed
> the problem, and it seems to me that something I did last Friday seems to
> have undone the SP2 fix, and I can't restore whatever has been undone!  I
> suspect that QuickTime is the culprit (with me accepting the updates which
> were available), but I have no hard evidence for that.

Please note, I must say it again, that Quicktime is not basically the
problem, it's just the application which triggers that behaviour by using
existing Windows API calls which have been designed for such applications.

The problem lies in Windows whose timekeeping is deranged if an application
like Quicktime uses those APIs.
> I didn't think that changing version would help, but it seemed both polite
> to the people who suggested it, and a "good thing" to have the latest
> version in any case.
> I have just started the QuickTime player, and I'll see if that makes any
> difference.
> Do you know a way to check if the MM times is enabled?  I could easily
> write a small piece of code do check this and enable them as an
> experiment.  Could you perhaps send me a copy of the patch?

I'm not currently aware of an easy way to find out if any application has
changed the MM timer resolution. 

I've observed that the timer APC callback function which is used by ntpd to
interpolate the system time between the timer ticks, and which is normally
called at regular intervals, is called with a jitter of +/- 1 millisecond
if the MM timer resolution is high. 

I can see if I can send you the patch which lets ntpd modify the MM timer
while it is active when I'm back at the office.
> Your help and suggestions are very much appreciated.


> David

Martin Burnicki

Meinberg Funkuhren
Bad Pyrmont

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