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

Martin Burnicki martin.burnicki at meinberg.de
Wed Dec 7 20:07:25 UTC 2005


David J Taylor wrote:
> I've had a QuickTime video playing but paused now for the last two hours
> or so,

As far as I can tell it's not necessary to play a video, just to have
Quicktime loaded, since it seems that Quicktime modifies the MM timer at
startup and changes back to default MM timer resulution when it exits.
Maybe other MM apps behavve differently, though.

> It's a bit early to say yet, but it looks as if a number of things have
> happened:
> - the drift value is changing from -65 downwards, currently -59.385
> - the offset has shot up to 120ms, but seems to be stable at that value (I
> guess if it goes up much more a step will happen at 128ms).

Maybe you've read in another current thread here that the current ntpd
version may not be very stable under Windows, so I've recently installed
and tested some other ntpd versions from earlier this year to find out
which one should be used preferably instead. Unfortunately I've found that
all of those versions adjust the Windows system clock VERY slowly. The
current version is much better in this regard, but as already said, it may
crash earlier or later.
> - the jitter figures seem much better, around 2 - 3ms.  Of course, that's
> with a high offset value so not strictly comparable.

That's what I've expected. However, I would expect the jitter figure being
constantly higher than without modified MM timer.
> However, it does perhaps suggest that:
> - the poor performance before was from the time switching into and out of
> MM mode.

> - having a permanently "on" MM mode may help this system, and may be a
> useful feature for NTP on some Windows systems.

Right. On the other hand, it might slightly decrease the synchronization
quality on a system which does not run MM apps at all.
> I still have no idea what piece of software started enabling the MM-timer
> mode last Friday, though!  I should keep better records.  I'll report
> again tomorrow.
> David


Martin Burnicki

Meinberg Funkuhren
Bad Pyrmont

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