On Thu, Nov 10, 2016 at 01:35:22PM -0800, Denny Page wrote:
> Here is the test setup: 3 identical hardware NTP units. Two accessible via 
> switch on igb0. One accessible vi igb3 as a directly connected IP point to 
> point. Here are test results:

Thanks for running the tests, much appreciated. Currently, it's not
(easily) possible to fully enable SW and HW timestamping at the same
time, so results of tests 2, 6, and 7 are as expected. I'm planning to
ask the kernel developers for some options that would allow that.

The mixed results in tests 3, 4 and 8 are not as expected, however.
Can you please try running one of those tests with 'acquisitionport
10000' in chrony.conf and post the debug output (after ./configure
--enable-debug) showing few exchanges?

I suspect it might be a bug in the kernel driver, occasionally not
getting or sending any transmit timestamp. I've seen some odd things
with the igb driver. But I think it could also be that your servers
respond so quickly that their response is received before the transmit
timestamp of the request. I'm not sure if by design that is allowed to
happen. If it is, that could complicate things quite a bit. It would
be interesting to see if it happens also with RX interrupt coalescing
enabled.

> test 3
> - hw stamps on for igb3
> - all ntp servers enabled
> - result: D K for servers attached via igb0, mixed D H and H H for server 
> attached via igb3
> 
> test 4
> - hw stamps on for both igb0 and igb3
> - all ntp servers enabled
> - result: H H for one server attached via igb0, mixed H H and D H for other 
> server attached via igb0, mixed H H and D H for server attached via igb3

> test 8
> - hw stamps on for igb3
> - ntp servers attached via igb0 disabled, server attached via igb3 enabled
> - result: mixed D H and H H

-- 
Miroslav Lichvar

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