"Joseph Gwinn" <[email protected]> wrote in message
news:[email protected]...
In article <[email protected]>,
"David J Taylor" <[email protected]> wrote:
> I have a small network of Windows XP (64 bit) running simulations,
> with
> NTPv4 running on all the boxes and using a GPS-based timeserver on
> the
> company network. The ping time to the server is 2 milliseconds from
> my
> desk, but I'm seeing random time errors of order plus/minus 5 to 10
> milliseconds, based on loopstats data.
>
> This level of timesynch error is OK for the simulation, but still
> that's
> a lot of error. I get far better on big UNIX boxes.
>
> The question is if this level of error is reasonable, given the
> setup.
> I know that timekeeping under Windows is not optimum, but cannot
> change
> the OS, so the question is if I have gotten things as good as they
> can
> be, or should I dig deeper. One thing that comes to mind is to raise
> the priority of the NTP daemon to exceed that of the simulation
> software.
>
> Thanks in advance,
>
> Joe Gwinn
Joe,
This is the performance I see:
http://www.satsignal.eu/mrtg/performance_ntp.php
The XP systems are:
Feenix: GPS-synched
Narvik: LAN-synced to Pixie (FreeBSD with GPS source)
These are all over the place. Both hardware and OS seem to matter, by a
lot.
Hardly "all over the place"! Feenix is well within a milliseconds, and
Narvik just within a millisecond, and programs on that OS can only read
the system time with ~16ms precision.
I can't add a GPS source, and I can't really control temperature.
So you need to keep the polling interval short.
I don't think that iburst is the issue, because the randomness persists
for at least a week, long after the iburst transients will have died
down.
I never said iburst was an issue, just that the systems will need to be on
for several hours before best accuracy is achieved. It's a pity that NTP
doesn't have a faster initial convergence.
My experience is the same. for average behaviour. But for use in
realtime, running the daemon at high realtime priority greatly reduces
the tails of the probability distribution of response times and/or clock
offsets.
Joe Gwinn
Yes, if the CPU loading is heavy I can quite believe that.
Cheers,
David
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