| Re: [chrony-users] Possible bug in PPS support |
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- To: chrony-users@xxxxxxxxxxxxxxxxxxxx
- Subject: Re: [chrony-users] Possible bug in PPS support
- From: Miroslav Lichvar <mlichvar@xxxxxxxxxx>
- Date: Mon, 23 Oct 2017 19:05:44 +0200
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On Mon, Oct 23, 2017 at 07:01:30PM +0200, Rob Janssen wrote:
> Miroslav Lichvar wrote:
> >
> > The last skew was 14 ppb, so it would take about 8 days to accumulate
> > 10 milliseconds worth of dispersion.
>
> Can you explain where the 10ms comes from? I know it is displayed in the "sources" output,
> but how is it calculated? It is way above the StdDev indicated in the "sourcestats".
> And of course it is also way above our usual accuracy.
It includes the root delay and distance. Check "chronyc ntpdata". Most
of that is probably the round-trip time to the server.
One point I forgot to make is that even if chronyd reselected
immediately after the reach value of the PPS refclock got to 0, like
ntpd does, checking stratum or selected source wouldn't be a reliable
way to monitor the accuracy, because the reselection wouldn't happen
if the NTP source was down too.
--
Miroslav Lichvar
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