[ntp:questions] chrony as a server

Rob nomail at example.com
Thu Feb 19 16:15:45 UTC 2015


Miroslav Lichvar <mlichvar at redhat.com> wrote:
> On Thu, Feb 19, 2015 at 02:42:39PM +0000, Rob wrote:
>> Ok but of course we are using PPS and a 16 second polling interval.
>> (or maybe the PPS refclock polls even faster although it displays 4 as
>> the poll interval indicator)
>
> You may want to try a shorter polling interval and see if the swings
> are still there. If poll 3 doesn't help, you can try even shorter, but
> normal timekeeping when the temperature isn't changing rapidly will
> likely get worse.

Well, as it is now we see no real "swings" as with ntpd, but more like
random spikes in each direction.  It was only my guess that these could
be lessened when chrony knows about clock rate changes beforehand.

The excursions are about ten times less than the swings in ntpd.

> The default PPS refclock driver poll is 0 (1s), this be changed too
> if the PPS signal has a higher rate. Some GPS units seems to have this
> configurable (e.g. ublox NEO-6T).

The PPS really is 1 PPS, but I am not sure if chrony is evaluating each
pulse separately or is averaging 16 pulse measurements into one clock
adjustment group.  (as it says poll 4)



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