Re: [chrony-users] Clock selection algorithm

[chrony-users@xxxxxxxxx]

I have changed the logging config like this:

 # tunable parameters
 driftfile      /var/lib/chrony/ntp.drift
 logdir         /var/log/ntpstats
-log            statistics measurements tracking tempcomp
+log            refclocks

i.e. I was logging some other things but I wasn't really using that.
After restarting chrony (I tried this on two different systems) I have not
yet seen the problem re-occur.  Looking in the refclocks logs I only see
some offsets of the e-03 order during the first minutes after startup,
not thereafter.
I will monitor the situation further to see if there it happens again.

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On 3/7/22 10:33, Miroslav Lichvar wrote:
> 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.
>


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