Hi,
I have tested different versions and setup of chrony the last few weeks. My goal is to get the most accurate and stable time possible from UTC using ntp and a gps timeserver.
My setup is pretty simple, linux boxes, one switch between everything. For my tests I am also using a third-party software as monitoring, connected via PTP and PPS on my timeservers, which does ntp polling (with hw timestamping) every second on the different clients and graph the offsets.
I started first with older versions of chrony (1.30) and got pretty good results, then tried to play with client side hardware timestamping and tested version 3.
The results with hwtimestamps were pretty good, especialy with a source that use hw timestamps as well, showing a very steady line on my monitoring system with a slight constant offset (+5us).. maybe due to an asymmetry somewhere ?
However I then noticed than all my chrony 3+ clients with hardware timestamping not enabled report suddenly an innacurate time with a constant offset to utc (approximativly -20 to -25 usec to utc) on my monitoring system. If i switch back to chrony 1.30, with the same configuration, the time offset is good again.
I first thought that there was a problem on the server side of chrony, but if I sync a 1.30 client on a 3+ client, it will report the same offset too.
Another behaviour i noticed on version 3+ with kernel timestamping is that for some server i can have very long poll time (60 seconds) even if i configured minpoll and maxpoll to shorter interval (0 & 1)
I tried version 2.4.1 and there are no such problem, so I assume it starts with version 3.0. I just tested the chrony 3.2-pre2 and the problem is still there.
Any idea where this could come from ?
Happy to provide more infos/data if needed