| Re: [chrony-users] Chrony offset and stability adjustments? (fwd) |
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On Tue, Jan 08, 2019 at 08:46:20AM +1300, Bryan Christianson wrote:
> My home LAN has an rpi3 + uptronics GPS hat providing NTP service.
> A linux host on the LAN runs 2 VirtualBox VMs - all 3 (host + VMs) using the rpi as their NTP server.
> All the machines are using chrony
>
> From the stats below you can see that root dispersion is < 100usecs on all the machines and that system time offset is better than 10usecs
In the estimate of the maximum error, it's important to include also
half of the root delay, so in your examples it would be about 250
microseconds.
Raspberry PIs have ethernet on USB, which adds some latency, and IIRC
the default interrupt coalescing is very large. You might want to try
setting a smaller rx-usecs value with ethtool -C, which should reduce
the root delay and give the clients a better estimate of the maximum
error.
Other small computers might be better suited for an NTP server. I have
a good experience with an Orange PI PC. The NIC is not on USB and the
driver supports SW timestamping. The only issue is with the GPU, for
which there is no open source driver, but that doesn't matter for a
server.
--
Miroslav Lichvar
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