[ntp:questions] Choice of local reference clock seems to affect synchronization on a leaf node

Dave Hart hart at ntp.org
Mon Nov 7 22:41:50 UTC 2011

On Mon, Nov 7, 2011 at 21:58, unruh <unruh at invalid.ca> wrote:
> Actually, that is not the way that ntpd works. It has no concept of
> "frequency error".

Sure does, the frequency error is the frequency= value reported by
ntpq, internally in ntpd stored in drift_comp, and persisted between
runs in the driftfile.  Perhaps you were thinking of short-term
frequency error due to temperature changes?

> All it knows is the offset. It then changes the
> frequency in order to correct the offset. It does not correct the offset
> directly.

The offset is corrected directly when it exceeds the step threshold,
128 msec by default.

> It never figures out what the frequency error is.

Sure it does, when started without a driftfile.

> All it does
> is "If offset is positive, speed up the clock, if negative slow it down"
> ( where I am defining the offset at "'true' time- system clock time").
>  (There is lots that goes into ntp's best estimate of the 'true' time,
> which is irrelevant to this discussion)

Irrelevant if you want to paper over the minimum delay clock filter,
which you love to disparage and I view as a key error reduction step.

Dave Hart

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