| Re: [chrony-users] Sources marked as falseticker which shouldn't be |
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- To: chrony-users@xxxxxxxxxxxxxxxxxxxx
- Subject: Re: [chrony-users] Sources marked as falseticker which shouldn't be
- From: Miroslav Lichvar <mlichvar@xxxxxxxxxx>
- Date: Tue, 7 Jan 2025 10:09:53 +0100
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On Mon, Jan 06, 2025 at 06:12:53PM +0800, Yuezhen LUAN wrote:
> But some of the chrony clients also mark B as falseticker, some marked B as
> combined, some marked B as selectable but not combined, and all chrony
> clients select C as current time source.
>
> Offset between B and C are small enough(currently 200us~300us). According
> to selection algorithm, I think B shouldn't be falseticker? 'chronyc
> selectdata -a -v' shows like this:
>
> [image: chronyc_selectdata.png]
That output shows that the sources A and B don't have any overlap in
their intervals and both overlap with C. This is a corner case in the
chrony selection algorithm that IIRC is handled differently than in
ntpd.
That overlap between A and C is only about 30 microseconds. A small
difference in the network delay, timestamping, etc could cause that
overlap to disappear, which would make make B lose the falseticker
status. That will also happen if A drifts further away from B and C.
--
Miroslav Lichvar
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