[ntp:questions] NTP 4.2.2p4 loopstats

TomD Thomas.Donovan at gmail.com
Sun Nov 12 18:21:59 UTC 2006

Wandering back to jg's original question...

It appears that the jitter field which gets written to loopstats
changed considerably between 4.2.0 and 4.2.2.

The new value, in the global variable clock_jitter, is calculated from
(last offset - current offset) rather than from the current offset as
in 4.2.0.
This new value is displayed by ntpq rv as "noise".

The old value is still around in the global sys_jitter.     ntpq still
displays this value as "jitter" in 4.2.2.
The sys_jitter value still gets updated, but not by ntp_loopfilter
anymore - which only updates clock_jitter.

This is significant to anyone who post-processes loopstats, as the new
values are typically smaller in magnitude.
I can't find anything about it in the bugs, docs, or mailing list.
Maybe I'm just not finding it.

A quick fix (...well, a quick ugly hack actually...), for anyone who's
loopstats post-processing has been disrupted with 4.2.2, is to change
the calls in ntpd/ntp_loopfilter.c to pass  sys_jitter  instead of
clock_jitter  to the 'record_loop_stats'  function.

Note that you probably don't want to change *anything* else in
ntp_loopfilter -  just the number which gets written to loopstats, lest
you disrupt the calculation of poll interval, etc.


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