Horrid balance-rr bonding udp throughput

I'm digging into some bug reports covering performance issues with 
balance-rr, and discovered something even worse than the reporter. My 
test setup has a pair of NICs, one e1000e, one e1000 (but dual e1000e 
seems the same). When I do a test run in LNST with bonding mode 
balance-rr and either miimon or arpmon, the throughput of the UDP_STREAM 
netperf test is absolutely horrible:

TCP: 941.19 +-0.88 mbits/sec
UDP: 45.42 +-4.59 mbits/sec

I figured I'd try LNST's packet capture mode, so exact same test, add 
the -p flag and I get:

TCP: 941.21 +-0.82 mbits/sec
UDP: 961.54 +-0.01 mbits/sec

Uh. What? So yeah. I can't capture the traffic in the bad case, but I 
guess that gives some potential insight into what's not happening 
correctly in either the bonding driver or the NIC drivers... More 
digging forthcoming, but first I have a flooded basement to deal with, 
so if in the interim, anyone has some insight, I'd be happy to hear it. :)

-- 
Jarod Wilson
jarod@redhat.com