Re: [chrony-users] Re: Question about large gap of offset on phc2sys with chrony

[Miroslav Lichvar <mlichvar@xxxxxxxxxx>]

On Fri, Aug 5, 2022 at 11:14 AM 심준영 <joonyoung.shim@xxxxxxxx> wrote:
> My problem is to cause too large gap between system clock and PTP hardware
> clock
> for a short while, whenever chrony synchronizes time from external NTP
> server
> (Poll is 6, so about 64 seconds) and then will affect to PTP hardware
> clock and
> system clock of the ptp4l slave machine.
>
> Are there any ideas to keep stable small gap even though using NTP like
> chrony
> to update system clock?

You can slow down the corrections of the system clock made by chronyd
by increasing the corrtimeratio (e.g. to 100 or 1000) and/or slow down
the corrections of the PHC made by phc2sys by setting smaller PI
constants (e.g. -P 0.04 -I 0.00024).

The latter will not make the offset reported by the server phc2sys
smaller, but it will make the clock easier for the clients to follow,
i.e. keep the offset between the clients smaller, which I assume is
what you are primarily interested in.

-- 
Miroslav Lichvar


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