[ntp:questions] NTP vs chrony comparison (Was: oscillations in ntp clock synchronization)
david at ex.djwhome.demon.co.uk.invalid
Thu Jan 24 23:46:56 UTC 2008
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).
> 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.
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