Re: [chrony-users] Accurately measuring clock drift

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On Mon, Jun 19, 2023 at 03:11:44PM -0700, Thangalin wrote:
> I'm wondering, in no particular order:
>    - Do the *esterror* values from calling *adjtimex()* yield an
>    apples-to-apples comparison between chrony and NTP?

The values are estimated differently. Not an apples-to-apples

>    - Do we need to combine PPS1 with the NTP server?
>       - If so, how?

Your configuration looks good to me.

>    - What else would we need to do to achieve sub-30 μs clock drift (or
>    sub-10 μs)?

That depends on the hardware. There might be a better way to timestamp
the PPS that doesn't involve interrupts. Is it an x86_64 machine?
See these two examples:

>    - How can we verify that the clock isn't drifting more than 30 μs,
>    programatically (i.e., what API calls return the recent clock drift
>    adjustment value)?

I don't think that is possible without a more accurate time source.

>    - What API call returns the most recent clock drift adjustment value in
>    nanoseconds?

This information is not available in the kernel (adjtimex). You would
need to use chronyc sources.

Miroslav Lichvar

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