Re: [chrony-users] Clock selection algorithm

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On Thu, Mar 03, 2022 at 07:23:30PM +0100, chrony-users@xxxxxxxxx wrote:
> But sometimes, probably due to interrupt latency, the offset of the PPS refclock has
> some spikes (e.g. spiking to 1 millisecond) and in this situation the PPS clock
> is sometimes marked as an outlier (x) because all the NTP refclocks are closer to the
> system time than this PPS sample is.  Chrony selects an NTP refclock and increases
> the stratum.  It spends some time (like 5-10 minutes) tracking the NTP servers before
> it reselects the PPS source.  This then alerts our monitoring system.

1 millisecond is a lot for an interrupt delay. If you enable the
refclocks log, how many subsequent samples do you see impacted? If
it's not too many, you could simply increase the polling interval and
let the median filter take care of the outliers.

If that doesn't work and you want to force chronyd to keep the PPS
refclock selected, you can set a larger delay for the refclock (e.g.
delay 0.005) to make it overlap with the other sources and avoid the
falseticker status.

Miroslav Lichvar

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