Re: Understand why system clock is bad even though chrony offsets look fine

On Fri, Apr 19, 2024 at 02:44:21AM +0530, Abhijith Sethuraj wrote:
> Hello,
> 
> I'm noticing issues with my system clock being inaccurate by almost 50us,
> even though "System time" in `chronyc tracking` shows offsets in the order
> of ns. This was noticed by an application that tried to get current time by
> calling `gettimeofday()`.

How did you measure that 50us error? Can you use that source of time
for synchronization?

> Root delay      : 0.000073557 seconds
> 
> Root dispersion : 0.000997235 seconds

Root distance (half of root delay + root dispersion) is over 1
millisecond here. That's an estimate of maximum clock error due to
asymmetries and clock instability.

> almost similar to "root dispersion"? Also, what recommendations do you have
> for monitoring chrony, so that I can catch this before it affects my app?
> Also, are there any config tweaks that I can try out here to help me?

You need a better server, one that has a smaller root dispersion and
hardware timestamping on both the server and client to get the maximum
error below 50 microseconds.

-- 
Miroslav Lichvar


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