On 2016-09-22 12:44:00 [+0000], Koehrer Mathias (ETAS/ESW5) wrote:

I run the cyclictest with the following options:
# cyclictest -a -i 100 -d 10 -m -n -t -p 80

there is -S. And then 100 might be a little tight.

Of course the 2 minutes run-time of cyclictest is only a rough first estimate.

and with no load…

Once I configure one of the i350 ports
# ifconfig eth2 up 192.168.100.100
the cyclictest shows directly and reproducibly significant larger max latency values (40 microseconds, using the same conditions).


I did the very same test with kernel version 3.18.27-rt27.
With that version I did not see anything like that.

Also, only the igb driver seems to cause the trouble. I have also an e1000e based NIC in this PC and 
the usage of this driver does not add any significant latency.

Any idea on this?

Does this also happen if you have the NIC up and you plug in / out the
cable? There are two things that come to mind:
  https://lkml.kernel.org/r/1445465268-10347-1-git-send-email-jonathan.david@ni.com
  https://lkml.kernel.org/r/1445886895-3692-1-git-send-email-joshc@ni.com

Thanks for any feedback

Best regards

Mathias

Sebastian