[ntp:questions] Second attempt at GPS-18 based NTP server

David Lord snews at lordynet.org
Thu Feb 2 20:24:44 UTC 2012


unruh wrote:
> On 2012-02-02, David J Taylor <david-taylor at blueyonder.co.uk.invalid> wrote:
>>> On NetBSD-5 with ntpd 4.2.6p5 the default is 64s.
>> I wonder what expertise they have to select polling for reference clocks? 
>> BTW: Paul has FreeBSD.
> 
> The reason for longer polling is a) network load, and b) rate
> optimality.
> If you are running ntp in order that your computer clock be ticking at
> exactly 1s/s, then longer polls are better (longer lever arm) if your
> computer clock does not change rate (eg due to internal temperature
> changes due to use of the computer) If, you want least deviationo of the
> clock from UTC shorter polls are better. Since the primary ntp noise
> source, variable network delays, is not there, and since the primary
> noise source is interrupt servicing delays, shorter is probably better.
> 
>>> I've just added the "minpoll 4 maxpoll 4" back to my ntp.conf
>>> as it could reduce the 30 usec offset blips I get when logs are
>>> rotated.
> 
> Not sure what would cause 30us blips. Are interrupts really being
> switched off by something for those lengths of time?

It's the load from log rotation and cron jobs running at
that time of night.


David Lord



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