RE: [chrony-users] chrony not observing maxpoll - bug?

["Charlie Laub" <charleslaub@xxxxxxxxxxxxx>]

I am still experiencing this problem and I am at a loss as to why. Perhaps I am not understanding what “update interval” means? I assume that if I have maxpoll = minpoll = N the update interval will be the poll interval times the filter length, and should not change? Is that correct?

 

Below is another example of output that I generated by printing out a selection of data from chronyc tracking. You can see the update interval increases from 32 seconds (expected value) to 182. I am polling a single server using these directives:

server 192.168.1.254 minpoll 2 maxpoll 2 filter 8 xleave

 

Update interval : 32.5 seconds Last offset : +0.003051660 seconds Frequency : 9.270 ppm fast

Update interval : 32.5 seconds Last offset : +0.000082686 seconds Frequency : 21.085 ppm fast
Update interval : 32.4 seconds Last offset : -0.000444030 seconds Frequency : 6.399 ppm fast
Update interval : 32.5 seconds Last offset : +0.000194910 seconds Frequency : 3.351 ppm fast
Update interval : 32.3 seconds Last offset : +0.000217533 seconds Frequency : 3.894 ppm fast
Update interval : 36.5 seconds Last offset : -0.002731794 seconds Frequency : 4.726 ppm fast
Update interval : 32.5 seconds Last offset : +0.000301728 seconds Frequency : 1045 ppm fast
Update interval : 32.4 seconds Last offset : +0.000134872 seconds Frequency : 3.236 ppm fast
Update interval : 32.5 seconds Last offset : +0.000149569 seconds Frequency : 4.055 ppm fast
Update interval : 32.4 seconds Last offset : -0.001271996 seconds Frequency : 0.241 ppm fast
Update interval : 36.5 seconds Last offset : +0.000269099 seconds Frequency : 6.121 ppm fast
Update interval : 36.5 seconds Last offset : +0.000269099 seconds Frequency : 6.121 ppm fast
Update interval : 121.6 seconds Last offset : -0.000647312 seconds Frequency : 5.888 ppm fast
Update interval : 121.6 seconds Last offset : -0.000647312 seconds Frequency : 5.888 ppm fast
Update interval : 121.6 seconds Last offset : -0.000647312 seconds Frequency : 5.888 ppm fast
Update interval : 178.6 seconds Last offset : -0.000680431 seconds Frequency : 5.881 ppm fast
Update interval : 178.6 seconds Last offset : -0.000680431 seconds Frequency : 5.881 ppm fast
Update interval : 178.6 seconds Last offset : -0.000680431 seconds Frequency : 5.881 ppm fast
Update interval : 182.6 seconds Last offset : +0.000140453 seconds Frequency : 6.125 ppm fast
Update interval : 182.6 seconds Last offset : +0.000140453 seconds Frequency : 6.125 ppm fast
Update interval : 182.6 seconds Last offset : +0.000140453 seconds Frequency : 6.125 ppm fast
Update interval : 174.6 seconds Last offset : -0.000026348 seconds Frequency : 6.119 ppm fast
Update interval : 174.6 seconds Last offset : -0.000026348 seconds Frequency : 6.119 ppm fast

 

 

From: Charles Laub <charleslaub@xxxxxxxxxxxxx>
Sent: Friday, February 5, 2021 2:42 PM
To: chrony-users@xxxxxxxxxxxxxxxxxxxx
Subject: [chrony-users] chrony not observing maxpoll - bug?

 

Background: I need to keep several machines well synchronized to my local NTP reference. This is for audio work, where playback needs to be tightly synchronized between multiple computers. I previously used NTP for many years for this, but have recently switched to chrony to take advantage of its time smoothing and filtering capabilities. I have a local "server" in my basement where the temp remains constant. It's a stable reference for other computers in my home. My machines only poll only this one sever.

 

On various Linux clients, I am experiencing the following issue:

 

Chrony works as expected. Synchronization is achieved to high precision, e.g. tens to few hundred microseconds.

I use a fixed polling interval by setting minpoll and maxpoll to e.g. 2

To keep track of what is going on I print out the last offset every 60 seconds in an ssh terminal session

I have noticed sometimes that this value gets "stuck". Here is some example output:

Last offset     : +0.001239868 seconds
Last offset     : -0.001022636 seconds
Last offset     : +0.000342921 seconds
Last offset     : -0.000313532 seconds
Last offset     : -0.001234458 seconds
Last offset     : -0.001234458 seconds
Last offset     : -0.000906603 seconds
Last offset     : -0.000906603 seconds
Last offset     : -0.000036374 seconds
Last offset     : -0.000354126 seconds
Last offset     : -0.000354126 seconds
Last offset     : -0.000010771 seconds
Last offset     : -0.000010771 seconds
Last offset     : -0.000010771 seconds
Last offset     : -0.000010771 seconds
Last offset     : -0.000411757 seconds
Last offset     : -0.000411757 seconds
Last offset     : -0.000411757 seconds

 

It dawned on me later that this should not be happening, and when I looked at the chronyc output I found this:

pi@SPKR-left:~ $ chronyc tracking
Reference ID    : C0A801FE (192.168.1.254)
Stratum         : 4
Ref time (UTC)  : Fri Feb 05 18:50:42 2021
System time     : 0.000003940 seconds fast of NTP time
Last offset     : +0.000011845 seconds
RMS offset      : 0.000603218 seconds
Frequency       : 6.857 ppm fast
Residual freq   : +0.000 ppm
Skew            : 0.059 ppm
Root delay      : 0.039830066 seconds
Root dispersion : 0.003487853 seconds
Update interval : 535.4 seconds
Leap status     : Normal

Notice the reported update interval of 535 seconds. But my server line includes the directives:

minpoll 2 maxpoll 2 iburst filter 8

The poll interval should remain at 2, and with filter=8 the poll should be reported every 32 seconds. 535 is certainly not the same as 32, so I suspect a bug.

 

This machine (Pi 4) is running chrony version 3.4, and another (an Intel box) is running 35. Both show an increase in the poll interval above 32 seconds in chronyc. When this happens, the synchroncity becomes relatively poor so I would like to find a way to fix this problem if possible.

 

Let me know if there is some other info I can post that might be useful.

 

Thanks,

 

-Charlie