David Woolley <[EMAIL PROTECTED]> writes: >David L. Mills wrote: >> >> The NTP discipline is basically a type-II feedback control system. Your >> training should recall exactly how such a loop works and how it responds >> to a 50-ms step. Eleven seconds after NTP comes up the mitigation
>You both have problems here. >Dave Mills: your problem is that you haven't explained why one should >continue to use a long time constant linear feedback system when a human >observer can easily tell you how to get within 10 microseconds of the >correct time after no more than about 3 samples. >Bill Unruh: you haven't explained what real world situation this test >is simulating; it is a standard doctrine that ntpd is not a substitute >for good hardware and system software (e.g. you shouldn't use ntpd to >get round lost clock interrupts). The real world situation that the test is run on (not simulating) is having a computer on a lan with another computer running ntp from a Garmin PPS acting as the server. It is a "best case" scenario, I will completely agee. I still get round trip times of msec rather than 150usec at times, the oscillators on the machines have glitches in which teh clock rate changes by 1-2PPS suddenly ( over less than 1/2 hr) and then long periods of quiescense. I have NOT tested the two in situations where there are longer paths, through many routers. I have not tested it on the road to Mandalay, or Indonesia. I have been looking at the real world response in a working system but where the network delays are minimal. Is my testing complete? Heavens no. It is one data point. Do I expect chrony to fall over on the road to Mandalay? Looking at its design, no, but experiments are the answer. >> algorithms present that transient to the loop and what happens >> afterwards conforms to the equations of control theory. Discussion about >> what happens at any time after that is a matter of mathematics and ntpd >> does conform to the mathematics as confirmed by observation and simulation. >That's an indication that the equations are inappropriate in that context. _______________________________________________ questions mailing list questions@lists.ntp.org https://lists.ntp.org/mailman/listinfo/questions