Re: [chrony-users] Sources marked as falseticker which shouldn't be

2025-01-07 Thread Yuezhen LUAN
Thanks Miroslav, that explains the behavior, I'll try explain this to our SA.

We can solve this by increase the three server's dispersion to 10ms or larger


Miroslav Lichvar  于2025年1月7日周二 17:10写道:
>
> 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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Re: [chrony-users] Sources marked as falseticker which shouldn't be

2025-01-07 Thread Miroslav Lichvar
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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