[chrony-dev] SW/HW timestamping on Linux

[Miroslav Lichvar <mlichvar@xxxxxxxxxx>]

The latest code in git now support SW and HW timestamping on Linux. It
should work with kernel 3.19 and newer. The new hwtimestamp directive
enables HW timestamping on the specified interface. If no interface is
specified, it will try to use SW timestamping. If the server or peer
is running chronyd with SW or HW timestamping, it's recommended to
enable the interleaved mode. A minimal config file for testing could
look like this:

server foo minpoll 2 maxpoll 2 xleave
hwtimestamp eth0
logdir /var/log/chrony
log measurements tracking statistics

You can see if it's actually working in the measurements log. With SW
timestamping the last two fields should be K K, with HW timestamping
they should be H H.

I've tested it with 82579LM, I210 and BCM5720 cards. I think the
results are pretty good, but there is still room for improvements.
It's a lot of new code, so please report if you see anything
suspicious. If you test the performance, I'm very interested in stddev
numbers comparing recent code (which can correct for asymmetric
jitter, but has no support for SW/HW timestamping) and the new code.

-- 
Miroslav Lichvar

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