[ntp:questions] peers with high offset on Intel Quad Core running Windows 2003

David Woolley david at ex.djwhome.demon.co.uk.invalid
Thu Aug 21 07:36:36 UTC 2008


Richard B. Gilbert wrote:

> Also note that Windows is a difficult environment!  The clock ticks at 
> something like 17 millisecond intervals.  If you really need/want time 

Recent versions of ntpd force multi-media timers on, which reduces the 
interval between ticks, at the cost of an increased risk in lost ticks. 
  Supposedly this was done because of having different measurement 
errors when they were on rather than off, and therefore having timing 
dependent on what application was running, but it also increases the 
accuracy.

The real problem, though, is that Windows does not interpolate between 
ticks in the kernel.  ntpd atttempts to do so in user space, but is 
rather vulnerable to scheduling delays, if the system is loaded, but 
ordinary applications will only see the time changing on a clock tick, 
not at about every microsecond, for older PC based Unix and Linux or 
every TSC tick for recent ones, particularly Linux.

> to the nearest microsecond, Windows is a poor choice of O/S.  There is 
> some way to interpolate between ticks which has been mentioned here from 
> time to time but I don't recall what it is.  I have no need for time to 
> the nearest microsecond on my Windows systems and have not tried to 
> memorize the details!

Yes.  Generally, if you care about timing to an accuracy of more than a 
few tens of milliseconds, you should not be using Windows.  Windows is 
optimised for human interfaces, so the most extreme timing it is 
designed for is probably that associated with playing simple MIDI files.




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