[ntp:questions] Dual-core systems - AMD - Windows Vista

Martin Burnicki martin.burnicki at meinberg.de
Tue Dec 4 16:15:19 UTC 2007


David,

David J Taylor wrote:
> Martin Burnicki wrote:
> []
>> I've just set up a new test under Vista, so let's see.
>>
>> What I can say right now is that the default tick adjustment value is
>> 156001 instead of 156250 which it used to be on earlier Windows
>> versions. Also the granularity of the system clock has changed from
>> 15.625 ms to 1 ms.
>>
>> Maybe the timer tick interpolation code is not quite appropriate for
>> these settings.
>>
>>
>> Martin
> 
> Martin, thanks for that interesting information.  I'd love to know if you
> see similar offsets to me, or if it's just a quirk of the system here.
> It's a test system and not a production one, so if you need anything
> tested just shout.  As you may have seen, I have been trying to get ntpd
> to compile here, but with little joy so far.

I had made a fresh installation of Vista and forgot to disable automatic
sleep mode, so my overnight test failed and I had to run it once more over
the last hours.

The test machine is a Intel Pentium D 3 GHz (dual core) with Windows Vista
x64. Data of the time synchronization performance was collected by the time
adjustment service which comes with the Meinberg driver package for
Windows. That service computes the difference between the Windows system
time and a built-in GPS170PCI card and normally disiplines the system time.
However, in order to test the accuracy of NTP the Meinberg time service was
configured just to collect data and not to apply any correnctions to the
system time.

I have run both the current NTP stable version ntp-4.2.4p4, and the current
ntp-dev version ntp-dev-4.2.5p104, configured to get the time from a GPS
controlled NTP server on the local network, which provides magnitues more
accuracy than we can see here.

Both versions of NTP showed similar dissatisfying results. The offset varies
from about 20 to more than 50 milliseconds, so there's a bias of about 30
to 40 milliseconds. See the following graph:
http://www.meinberg.de/download/ntp/graphs/ntp-dev-4.2.5p104-windows-vista-x64.pdf

In order to show that it's possible to yield better results even on a 64 bit
platform I have disabled the NTP service and enabled our time adjustment
service start to discipline the system time. The results can be seen at the
end of the graph. 

In order to make the results better visible I've also generated another
graph with different scaling of the time offset:
http://www.meinberg.de/download/ntp/graphs/ntp-dev-4.2.5p104-windows-vista-x64-details.pdf

Please note both NTP and our time adjustment service are simple 32 bit apps
compiled with VC6, so as a conclusion we can say that there is neither a
general problem with the 64 bit OS nor with the 64 bit hardware
architecture.

As already mentioned earlier I _assume_ there is a glitch in the NTP code
which doesn't convert or interpolate the Windows time stamps properly under
Vista.

I'll try to find out more.

Martin
-- 
Martin Burnicki

Meinberg Funkuhren
Bad Pyrmont
Germany




More information about the questions mailing list