[ntp:questions] NTP Performance on WINNT
david at ex.djwhome.demon.co.uk.invalid
Sat Jul 25 16:58:30 UTC 2009
> Hi David, I am wondering is there any other means to profile NTP
> performance, like some kind of hardware setup to measure time offset
> of two machine?
You need access to the source code of the clock interrupt service
routine and the ability to directly right to something like a parallel
port if you want to measure the true offset (relative to something like
GPS pulse per second). The former, at least, you are not going to get
under a closed source OS, like WINNT.
Also remember that Windows never gives the time to application programs
to better than 1ms, and this can degrade to more like 16ms. Also
Windows offers no guarantees of scheduling latencies between real
external events and when application code runs to service them.
Another option might be to install some sort of clock card that can be
read through a low latency device driver, but then you would be better
using that synchronised clock card, rather than the software clock, for
Although you might be able to drive a real (non-USB) parallel port, from
application code, with fairly low latency the results would only be
meaningful for a very unloaded machine, as, on a loaded machine, you
wouldn't really know where you where in the system tick interval, when
you read the software time.
I'd suggest, therefore, that you will need to write a device driver, for
good accuracy, and be Microsoft or their subcontractor, for full accuracy.
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