David L. Mills wrote: > Roman, and others, > > You should tae a closer look at the code in ntp_loopfilter.c. It throws > nothing away. The main tool for adaptation to unstable clock oscillators > is to vary the time constant according to measured stability. You will > note the response to observed frequency transients is to reduce the poll > interval and increase it when the transient subsides.
I am not concerned about response to unstable oscillators, but response to sudden offset changes, due to causes external to ntpd. for example, one of my servers that missed the leap second: 53736 12.250 -0.000257957 27.539499 0.001335174 0.001348 6 53736 915.986 0.000000000 -500.000000 0.027077495 553.713302 4 53736 1205.339 0.116974652 -499.553777 0.155550337 479.529838 6 53736 2168.334 0.000000000 -95.763792 0.227084448 461.761017 4 53736 2423.070 0.000000000 -95.763792 0.196824591 399.896771 6 53736 3069.263 0.000000000 185.642644 0.042492463 373.812074 4 ... 53736 4429.382 -0.127968047 180.096602 0.026710882 28.070739 6 53736 5453.172 0.000000000 40.199238 0.030830475 74.052636 4 with the associated time steppings: 1 Jan 01:03:27 ntpd[326]: synchronized to GENERIC(0), stratum=0 1 Jan 01:15:15 ntpd[326]: time reset -1.000113 s 1 Jan 01:15:15 ntpd[326]: frequency error -1080 PPM exceeds tolerance 500 PPM 1 Jan 01:36:08 ntpd[326]: time reset +0.426068 s 1 Jan 01:51:09 ntpd[326]: time reset +0.259175 s 1 Jan 02:30:53 ntpd[326]: time reset -0.181635 s (time is MET) so it looks like ntpd stumbles when it suddenly notices a large offset it cannot explain: it assumes that the frequency changed by a horrible amount. or when it starts up: 53723 26953.191 0.000160889 4.994171 0.000002000 0.009279 6 ..reboot.. 53723 30097.210 -0.015328167 -40.855911 0.000137179 22.803956 4 53723 30161.197 -0.005654889 -41.046219 0.004743029 19.749034 6 even with ntpdate before ntpd or so it is rather difficult to ensure a near-zero offset at boot time. In the example here the offset after bootup was only 15ms, but ntpd yanked to long-term frequency of 4.99 to -40 and it took it about 6 hours to slowly crawl back to the long-term value. Roman _______________________________________________ questions mailing list [email protected] https://lists.ntp.isc.org/mailman/listinfo/questions
