On Wednesday 06 October 2010 19:14:42 Krishna Kumar2 wrote: > Arnd Bergmann <arnd@xxxxxxxx> wrote on 10/06/2010 05:49:00 PM: > > > > I don't see any reasons mentioned above. However, for higher > > > number of netperf sessions, I see a big increase in retransmissions: > > > _______________________________________ > > > #netperf ORG NEW > > > BW (#retr) BW (#retr) > > > _______________________________________ > > > 1 70244 (0) 64102 (0) > > > 4 21421 (0) 36570 (416) > > > 8 21746 (0) 38604 (148) > > > 16 21783 (0) 40632 (464) > > > 32 22677 (0) 37163 (1053) > > > 64 23648 (4) 36449 (2197) > > > 128 23251 (2) 31676 (3185) > > > _______________________________________ > > > > > > This smells like it could be related to a problem that Ben Greear found > > recently (see "macvlan: Enable qdisc backoff logic"). When the hardware > > is busy, used to just drop the packet. With Ben's patch, we return > -EAGAIN > > to qemu (or vhost-net) to trigger a resend. > > > > I suppose what we really should do is feed that condition back to the > > guest network stack and implement the backoff in there. > > Thanks for the pointer. I will take a look at this as I hadn't seen > this patch earlier. Is there any way to figure out if this is the > issue? I think a good indication would be if this changes with/without the patch, and if you see -EAGAIN in qemu with the patch applied. Arnd -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
