On Wednesday 06 October 2010 19:14:42 Krishna Kumar2 wrote:
> Arnd Bergmann <a...@arndb.de> 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
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