Re: [chrony-dev] Question / Feature suggestion - trimrtc on start?

[Ed W <lists@xxxxxxxxxxxxxx>]

Hi, a good repost, but...

> Thus calling trinrtc at anytime while running should not
> make a difference. But doing it on bootup seems not a good idea. The system
> time is not good then.

I'm not seeing why it makes a difference what the system time is at this
point? In fact by definition the system time at this point will simply
be the RTC time + estimated offset?

Essentially, the goal at boot would be to step the RTC by the estimated
offset and maintain the current estimated drift params. Much later we
will learn that the step wasn't correct, but hopefully it's better than
nothing.

(Case in point is that my clock has drifted by 20 seconds over some
period of not running trimrtc. The bootscripts all see a time of some 20
seconds slow until chrony starts, then they see a 20 second jump and a
few things get upset? I outlined a few ways to fix this, but trimrtc on
every boot reduces the scale of the problem somewhat for my requirements)

> You should wait until the system time has settled down.

This would only appear to be useful from the point of view of improving
the estimate of drift? (arguably we get an update on the size of error
between real time and RTC, but my question was how often we can sensibly
use that to update the RTC without upsetting our current drift measurements?

> Note that I believe hwclock now also estimates the rtc drift rate as
> well, so chrony's rtc stuff is of less use now.

I wasn't aware that it now did an automatic estimate?  The version I
have doesn't seem to do that, and in any case it would seem to rely on
the box being correctly shutdown for it to update it's drift rate
estimate?  Chrony appears to give a realtime update of estimate

> The other problem is that the drift rate is highly temperature
> dependent. 

Sure - remember it's a router that isn't permanently connected to the
internet.  We can do the best we can, but clearly it will be imperfect.
 Adjusting for clock drift appears *likely* to be beneficial to accuracy
despite the change in drift between on/off (I get that there exist
situations where this wouldn't be true and likewise I haven't measured
my situation either)


> There is an argument for
> not having the rtc stuff in chrony anymore.

I guess I will measure and try to estimate the effect

I would say that there is more of a case for ditching hwclock from init
scripts though?

Cheers

Ed W

---
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.