And I thought I was asking such a simple question... :) Many thanks to all who took the time to enlighten me.
For the record, TomD's patch works well. As to whether sys_jitter or clock_jitter is a better indicator of performance, I am certainly not going to presume to differ with those far more qualified than I. jg David L. Mills wrote: > TomD, > > There are several jitter statistics now, including per-association > jitter and system jitter. These statistics are averages of first-oder > time differences. It became apparent that frequency differences are a > valuable indicator of equipment malfunction, A/C failure and so on. I > could have simply tacked on an additional field, but there would be many > more guys than just you out for my scalp. The old statistic wasn't very > useful anyway. Take it from me and my own monitoring stash that you > really want the frequency differences, properly interpreted as wander or > maybe noise, but not jitter in the normal techical interpretation. > > The intended interpretation of loopstats is, as the name suggests, > watching the discipline loop time, time differences, frequency, > frequency differences and time constant (poll interval). From long > experience, these xstatistics are really what you need to know. Watch > the ;noise over a day or two; see how exquisitly sensitive it is. > > Dave > > TomD wrote: >> 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. >> >> -tom- >> _______________________________________________ questions mailing list [email protected] https://lists.ntp.isc.org/mailman/listinfo/questions
