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- To: chrony-users@xxxxxxxxxxxxxxxxxxxx
- Subject: Re: [chrony-users] Relationship Between Chrony and NIC Clocks
- From: Miroslav Lichvar <mlichvar@xxxxxxxxxx>
- Date: Thu, 22 Oct 2020 09:47:15 +0200
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On Wed, Oct 21, 2020 at 11:27:54PM -0500, Scott Stephens wrote:
> Thanks, that's very helpful. It sounds like it could cause problems if
> something outside of chrony is synchronizing a NIC clock used by chrony for
> hardware timestamping, even if it's synchronizing it to the system clock.
> Am I understanding that correctly?
Yes, that could certainly cause issues. It might work, but the
adjustments would have to be very slow to not disturb the chronyd's
loop, e.g. phc2sys using small PI constants. Synchronization with
ptp4l to a stable external PTP source would work better.
> It would be nice for my application to
> be able to synchronize the NIC clock as well as the system clock. It's
> network capture related, so the most important timestamps are being done
> with NIC hardware timestamping.
If all your NTP sources are on the same interface, you could try this
patch I mentioned before:
https://www.mail-archive.com/chrony-users@xxxxxxxxxxxxxxxxxxxx/msg01881.html
You could use one chronyd instance to synchronize the PHC and another
chronyd or phc2sys instance to synchronize the system clock to the
PHC.
--
Miroslav Lichvar
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