| Re: [chrony-dev] PPS reference clock rejected because of high dispersion |
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On Tue, May 20, 2014 at 11:41:39AM +0200, Hattink, Tjalling [FINT] wrote:
> When the offset between the PPS and SHM clocks is bigger than 0.5 / rate
> the PPS samples are rejected. So if both refclocks disagree only the SHM
> will actually publish samples. This shouldn't mark the SHM refclock as
> falseticker right?
Not sure where exactly is this coming from, but with your patch I'm
seeing this:
sources.c:711:(SRC_SelectSource)[20-10:58:03] Can't synchronise: no majority
sources.c:913:(SRC_SelectSource)[20-10:58:35] Selected source PPS1
sources.c:711:(SRC_SelectSource)[20-11:21:50] Can't synchronise: no majority
sources.c:913:(SRC_SelectSource)[20-11:22:06] Selected source PPS1
sources.c:711:(SRC_SelectSource)[20-11:39:12] Can't synchronise: no majority
sources.c:913:(SRC_SelectSource)[20-11:39:44] Selected source PPS1
sources.c:711:(SRC_SelectSource)[20-11:41:37] Can't synchronise: no majority
sources.c:913:(SRC_SelectSource)[20-11:41:53] Selected source PPS1
> > Hm, maybe it would make more sense to introduce a new maxdispersion
> > refclock option to ignore filtered samples and not update the variance
> > statistic when the dispersion is too large? For the PPS refclock it
> > could be by default 0.1 or so to prevent the original problem with
> > chronyd ignoring the raw samples completely.
>
> I'm not sure exactly where you want to do this check. The dispersion
> calculated at the beginning of RCL_AddSample and RCL_AddPulse is
> actually based on the average dispersion from the filter. I don't see
> how rejecting samples when the filter result is too big will help making
> the average dispersion lower, as you will get in the same deadlock
> situation again. Rejected samples do not update the filter, so the
> average dispersion will never get lower anymore.
If you do it in filter_get_sample() before the variance stat is
updated, it should never be larger and it shouldn't stuck.
--
Miroslav Lichvar
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