Re: [chrony-dev] [RFC] Transparent fallback from NTP reference clock to RTC

[Ahmad Fatoum <a.fatoum@xxxxxxxxxxxxxx>]

Hello Miroslav,

Thanks for your feedback.

On 3/25/25 14:46, Miroslav Lichvar wrote:
> On Mon, Mar 24, 2025 at 04:26:31PM +0100, Ahmad Fatoum wrote:

[snip]

>>   - rtcsync when the RTC is a selected reference clock should be a no-op
>>
>>   - rtcsync when the RTC is _not_ the selected reference clock should
>>     periodically program the time into the RTC like the kernel usually
>>     does, once the drift exceeds a threshold
> 
> This looks like a significant complication. I prefer to keeps things
> simple if possible, avoiding fallbacks and switching between different
> modes of operation.

I am open to less complicated ways to achieve this that don't require us
to restart chrony with different configs.

> Have you considered using the local option for the RTC refclock?

I was not aware for it and will try it out.

> I.e. use it only for stabilization of the system clock, not as a time
> source. That would work even when it's synchronizing to NTP servers.
> When NTP is not reachable, it would activate the local reference as
> configured by the local directive. I guess something would be needed
> for the case when it's started without NTP.

Do you have a suggestion how to go about it? I also think that even if
local works for us, we still need to address the synchronization of the
RTC to system time when the system is NTP-synchronized.

Currently, chrony disallows rtc reference clock to co-exist with
rtcsync, but maybe we should allow it and enable the rtcsync only when
NTP is reachable and the RTC is local and not activated?

Thanks,
Ahmad

-- 
Pengutronix e.K.                  |                             |
Steuerwalder Str. 21              | http://www.pengutronix.de/  |
31137 Hildesheim, Germany         | Phone: +49-5121-206917-0    |
Amtsgericht Hildesheim, HRA 2686  | Fax:   +49-5121-206917-5555 |


-- 
To unsubscribe email chrony-dev-request@xxxxxxxxxxxxxxxxxxxx with "unsubscribe" in the subject.
For help email chrony-dev-request@xxxxxxxxxxxxxxxxxxxx with "help" in the subject.
Trouble?  Email listmaster@xxxxxxxxxxxxxxxxxxxx.