Re: [chrony-users] Bug report: `maxslewrate` violation by chrony

Thank you, this indeed appears to be our issue.

On Tue, Dec 6, 2022, 00:47 Miroslav Lichvar <mlichvar@xxxxxxxxxx> wrote:

On Mon, Dec 05, 2022 at 05:14:10PM -0800, Adam Snaider wrote:
> Hi folks,
>
> I wanted to report a bug. We use chrony for time synchronization and we
> have a strict requirement that forces us to limit the slew rate to no more
> than 250ppm. We noticed that in some conditions, chrony exceeds this limit
> by >10x. I've collected an strace that shows chrony is indeed the culprit
> as it is calling the clock_adjtime syscall with the tick and frequency set
> to 9980 and -140765 which corresponds to roughly -2002ppm.

The values passed to clock_adjtime() correct both the estimated
frequency error (drift) and phase error (slew). What frequency do you
see reported in the tracking log when this happens?

If I understand your test correctly, you are simulating an unstable
clock, which could be measured as a large frequency offset.

If you need to limit the sum of the two, you will need to set also
the maxdrift option.

--
Miroslav Lichvar

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