Re: [chrony-users] Root delay and Root dispersion values in `chronyc ntpdata'

[Chris Perl <cperl@xxxxxxxxxxxxxx>]

On Mon, Jun 26, 2017 at 9:28 AM, Chris Perl <cperl@xxxxxxxxxxxxxx> wrote:
>> The reason why they are always 15 microseconds is that the fields have
>> a 32-bit fixed-point format with ~15 microsecond resolution and
>> chronyd as a server rounds them up. So, if it calculates its delay and
>> dispersion as 1 microsecond, they will still be rounded to 15
>> microseconds. It's a limitation of the NTPv4 protocol. I'd like to
>> improve this in NTPv5 when the NTP WG starts working on a new version.
>>
>> If you wanted to get a more accurate root distance on the client, you
>> could set the delay of the SHM refclock on the server to 0 and add
>> half of the delay to the precision instead. I think it might have a
>> small effect on the timekeeping performance though.
>
> That is very helpful.  Thanks!

Are there any similar tricks to be able to get a more accurate root
dispersion on clients?  In the setup I've been testing, chrony on the
server generally reports a root dispersion of about 1us.  But, this is
getting rounded up to 15us due to the aforementioned fixed-point
format.

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