[ntp:questions] Extracting ntpq like information programmatically

Mischanko, Edward T Edward.Mischanko at arcelormittal.com
Sat Mar 30 05:23:05 UTC 2013

What can be done with ntpd's code to address the lack of speed in ramping
down the time constant as needed to keep up with changes in the local clock?

> You are observing on a time scale much shorter than the loop time
> constant.  ntpd has an adaptive time constant, and once it has gained
> initial lock, that becomes quite long, as it assumes that offsets are
> due to measurement errors, e.g. due to differential delays out and
> return.  Also, in your case, you may actually have been using the same
> best sample for the whole 15 minutes.
> This strategy will generally give the best solution if the temperatures
> of the oscillators are stable.  Where ntpd can have problems is in not
> ramping down the time constant fast enough if the temperature changes
> and the local clock frequency changes.
> I'm not sure of the exact oversampling rate, but even after the
> approximately 1 out of 8 sampling for the best of the last 8, I believe
> it is still oversampling in relation to the loop time constant.
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