[ntp:questions] strange behaviour of ntp peerstats entries.

David L. Mills mills at udel.edu
Sun Feb 3 20:56:50 UTC 2008


Not quite. There must always be a selection in every run of eight 
samples, so there can be no more than seven unselected samples in a row. 
To gain more insight, run ntpd with -d to produce a trace. Note in the 
clock_filter trace the age value, which is the interval from the last 
selected minimum sample to the current time.

In passing, the clock_filter statistics in that trace refer to the 
minimum sample, not the current sample. That should probably be changed.


Bill Unruh wrote:

> David Woolley <david at ex.djwhome.demon.co.uk.invalid> writes:
>>Unruh wrote:
>>>Under ... is the line
>>Apologies, I missed that detail.  I guess dst has changed its meaning 
>>over time.  (It doesn't really look right to me though, as there is a 
>>sudden discontinuity as you cross the Allan Intercept.)
>>However, that doesn't change the fact that the sample used is ord[0], 
>>i.e. the sample with the lowest dst value, subject to it also being 
>>newer than the last one used.  That is not necessarily the most recent.
> It looks like you are right that it does not only select it if it is the
> latest. Comparing the peerstats output ( augmented by the most recent
> p_offset and p_del) and the loopstats, there is a loop output whenever the
> min changes, not only if it is the latest as well. I must have misread the
> code. Sorry. But that still can result in 8 measurements without any being
> used. 

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