Re: [chrony-dev] refclock prefer and log

[Miroslav Lichvar <mlichvar@xxxxxxxxxx>]

On Sat, Nov 28, 2009 at 08:28:17AM +0100, Håkan Johansson wrote:
> I'm testing chrony (current git) with two GPS reference clocks, but
> am suffering from chrony moving between the two equally good sources
> as reference clock.
> 
> It would be nice with an option akin to the ntpd 'prefer' to force
> one of the two (when it is an eligible source, i.e. OK for sync).

The delay option can be used to help chrony select the "better"
source.

When I have configured the same PPS signal as a LinuxPPS refclock and
as a SHM refclock via gpsd, there is a ~24us offset between them and
they both have very low jitter so they don't overlap and cause the
"no majority" error message.

Specifying a higher delay for the SHM refclock fixes the problem.

refclock SHM 1 delay 2e-4
refclock PPS /dev/pps0

Adding support for prefer keyword shouldn't be very hard, but I think
there will need to be a special refclock handling in the source
selection routine to address the overlapping problem, now refclocks
are treated exactly the same as NTP sources.

> ntpd also has a keyword 'noselect' which prevents a server from
> being used as reference clock.  I've found that quite useful to let
> a good ntpd instance do monitoring of other machines, without the
> risk of them being used as reference.

That would be useful.

> As far as I could see, refclock measurements in chronyd are not
> logged to any file?  It could be nice with a
> /var/log/chrony/refclock.log or something such, updated on each
> successful dpoll.

Good idea.

Thanks for the suggestions.

-- 
Miroslav Lichvar

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