[ntp:questions] NTPD_USE_INTERP_DANGEROUS was ARRGH!!! I woke up to a 50 SECOND clock error.

Ron Frazier (NTP) timekeepingntplist at c3energy.com
Sun Mar 18 14:17:28 UTC 2012

I'm forking the subject line, which didn't really seem relevant any more.

more below

On 3/18/2012 7:01 AM, David J Taylor wrote:
> "Ron Frazier (NTP)" <timekeepingntplist at c3energy.com> wrote in message 
> news:4F65006D.4090205 at c3energy.com...
> []
>> Come to think of it, my comment about the polling interval not 
>> increasing may only apply to a local refclock, not a local server.
> You may be right - all the servers on this test system are Internet 
> servers.
>> Can you elaborate more about what NTPD_USE_INTERP_DANGEROUS does?
>> Sincerely,
>> Ron
> Overnight results are here:
>  http://www.satsignal.eu/ntp/Win-8+Internet.html
> As you can see, jitter is under a millisecond, with the local 
> (noselect) server showing about half a millisecond of jitter, and the 
> Internet servers between about 3 and just over 6 milliseconds.

 From my point of view, those look pretty good.  Those peerstats graphs 
come in pretty handy.

> NTPD_USE_INTERP_DANGEROUS if set, forces interpolation on Windows.  
> With Windows XP or earlier, Interpolation works well, but not on Vista 
> or later, so under certain conditions, NTP disables interpolation as 
> mentioned here:
>  http://lists.ntp.org/pipermail/questions/2011-November/030904.html
> You can enable interpolation, and you may get better results.  If not, 
> jitters will have a floor of about 0.977 milliseconds.
> Cheers,
> David

What's the dangerous part?  Are we just talking lots of CPU churning?  
If so, can I just shut down NTP and tweak it?




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Ron Frazier
timekeepingdude AT c3energy.com

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