[ntp:questions] NTP Bug 2328 - Vista/Win7 time keeping inaccurate and erratic

David Taylor david-taylor at blueyonder.co.uk.invalid
Thu Nov 28 08:33:12 UTC 2013


On 27/11/2013 17:48, Martin Burnicki wrote:
> David Taylor wrote:
>> Thanks, Martin, that's most interesting.  I can get nothing like that
>> performance from my Win-7 systems, although they are all connected via
>> Wi-Fi which doesn't help.  I've just changed the order in my MRTG
>> presentation to show XP, versus  Vista, Win-7, and Win-8.  As you'll
>> see, there's nothing like the smooth graph you got from Win-7, although
>> these are offsets reported by NTP rather than measurements against a PCI
>> reference like yours. However, the offset scale is different, as I have
>> a range of +/- 3 milliseconds, and your is +/- 30 milliseconds, so
>> perhaps your noise would be the same as mine once the graph was scaled.
>
> OK, here's another graph from the same data, with +/- 3 ms time offset
> range, but a longer time:
> http://support.ntp.org/people/burnicki/windows/bug2328_workaround_fine.pdf
>
> My setup is using a Linux NTP server on a local LAN, connected via
> cable, so I'd expect this yields a better accuracy than a WiFi connection.
>
> Also, the time offset is not the offset reported by ntpq -p, but the
> offset of the Windows system time (disciplined by ntpd) compared to the
> time from a built-in GPS PCI card.
>
>> Maybe my Win-7 systems are the unaffected ones?
>
> Possibly.
>
> We have also seen setups (under Windows) where time synchronization is
> very smooth versus systems where time synchronization steps back and
> forth by 1 ms or so. My *assumption* is that a possible reason could be
> the sign and/or the absolute mean frequency offset, which may cause
> rounding errors or so in the Windows kernel when converting 1 ms ticks
> to nominal tick adjustment count which is 15.6 ms, or vice versa.
>
>> Did the one you tested have any NTP environment variables set, to
>> enable/disable interpolation etc. etc.?
>
> No, I just used the default installation, and replaced the binaries later.
>
> Martin

Plenty to think about there, Martin!  I will see if I can move a Linux 
server (Raspberry Pi with GPS/PPS) to be next to the Win-7/64 system 
under test (PC Molde) and have it sync to that server.  I did check and 
I have no environment variables set either.  This is an Intel Atom 
system, and I should check the BIOS that no power-saving, frequency 
changing measures are in place.

I wish I could say it was all fixed in Windows-8, but it /is/ better there.
-- 
Cheers,
David
Web: http://www.satsignal.eu



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