Re: [v2 RFC PATCH 0/4] Implement multiqueue virtio-net

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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?

Thanks,

- KK

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