I have a 12 CPU server with 3 4-port 82576 network cards (12 ports
total using igb driver).  It's running Debian 7 (3.2 kernel with the
realtime patches).

I have a process on that system that is reading from a virtual tap
interface every 20ms (using boost::asio) and writing udp packets out
one of the igb ports.  If I bring down or configure one of the other
interfaces not related to that process, that process goes to sleep for
a little over 200ms (fairly consistent, 205-220ms) and misses 10 of
its timeslots.

If I bring down the e1000 82574L interface on the motherboard, I don't
see this problem.

I tried running ftrace on my process, but it didn't tell me much.  It
seems that while I was bringing the interface down, the process
switched CPUs, but there was a 200ms delay (closer to 300ms with
ftrace running) between when it stopped on one CPU and when it started
on another.

I tried it with the stock 3.2 igb driver and also with the igb 5.1.2
driver, same problem.

Any suggestions on how to troubleshoot?

Thanks,
Aaron

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