[ntp:questions] how to change the runtime priority of NTPD on Windows

David J Taylor david-taylor at blueyonder.co.uk.invalid
Thu Feb 9 06:24:29 UTC 2012

> Hello.  I'm not sure who to address my reply to.  Thanks for the link to 
> the configuration info.  Here are a couple of quotes from it:
> -M
>    Raise scheduler precision to its maximum (1 ms) using
>    timeBeginPeriod. (Windows only)
> -P /priority/
>    To the extent permitted by the operating system, run the ntpd at the
>    specified priority.
> It doesn't appear to me that -M is related to process priority, but to 
> internal scheduler timing.  I tinkered around with the -P parameter a 
> little, but couldn't detect any changes.
> Sincerely,
> Ron


The use of -M enables the Windows MultiMedia timer, which raises the rate 
of one of the internal clocks from a ~15 millisecond interval to a ~ 1 
millisecond interval.  Without -M, on Windows XP at least, the good 
timekeeping of NTP is disturbed by the several millisecond transient which 
happens when another program enables or disables the MM timer (such as the 
Media Player).

Therefore in case you have any programs which use the multimedia timer, 
it's best to set the -M option so that MM timer is permanently running 
while NTP is running, and there are no transients.


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