Today I changed the configuration file of two of my NTP servers to enable the kernel timekeeping discipline, and have put plots of the effect of the change at http://www.febo.com/time-freq/ntp/stats/kernel_discipline/index.html.
The data is derived from the offset and dispersion fields of the peerstats file. When using kernel discipline, the offset and jitter shown by the ntp stats are essentially 0, which makes sense since both the reference and the unknown time come from the same source; they should track each other closely. When not using kernel discipline, there is a wander of several hundred microseconds in one case, and several milliseconds in the other, and significantly more jitter in both cases. My question is about that wander -- is it showing the (in)stability of the crystal on the motherboard, *or* is it simply showing that NTP by itself doesn't steer the system time as tightly as the kernel discipline? Put another way, can I make any observations about the quality of the motherboard crystal from this data, or am I looking at NTP's PLL performance? Bottom line, I'm trying to explain what these plots tell me, other than the fact that I need an external reference to evaluate the performance of the NTP/PPS system. Thanks, John _______________________________________________ questions mailing list [email protected] https://lists.ntp.isc.org/mailman/listinfo/questions
