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