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RE: [Xen-devel] vif interface dropping 80% packets

  • To: "Reese Faucette" <reese@xxxxxxxx>, <xen-devel@xxxxxxxxxxxxxxxxxxx>
  • From: "Ian Pratt" <m+Ian.Pratt@xxxxxxxxxxxx>
  • Date: Tue, 6 Feb 2007 23:59:19 -0000
  • Delivery-date: Tue, 06 Feb 2007 15:59:27 -0800
  • List-id: Xen developer discussion <xen-devel.lists.xensource.com>
  • Thread-index: AcdKR7U3m2Zq3uiQQHK/fHhAcjCz4gAAcP9g
  • Thread-topic: [Xen-devel] vif interface dropping 80% packets

> > I've seen rather better figures than this with another 10G card.
> > Does your NIC/driver support TSO and LRO?
> yes to both, and have tried with LRO both enabled and disabled.
again, the
> dom0 performance is fine, it's just to domU that is slower.  I have
> bridging set up on this interface, i.e. peth2, eth2, xenbr2, etc. - is
> not the way I should be doing it?

I presume this is a box with >1 core? Try running dom0 and the domU with
one VCPU to keep things simple. The scheduler should put them on
different physical CPUs.

The packets are getting dropped being passed from the bridge into the
domU, because the domU isn't keeping up and creating slots in the ring
buffer. For a TCP connection, this is surprising as you'd have to have a
big socket buffer to saturate the ring buffers. Switching to 3.0.4 or
unstable will certainly help. 

You could try putting netback.queue_length=256 on the module or dom0
kernel command line, but a better fix would be to increase the ring
buffer size.

> >> 2) if yes, Will the patch "fedora-36252.patch" work on the 2.6.16
> >> kernel included with 3.0.4, or have conflicts crept in?
> >
> > No idea. What does the patch do?
> This was the mythical patch to make 2.6.18 into a Xen-aware kernel.
> me
> forever to track it down - is there a more obvious place to look?
Sorry to
> just refer to the file by name, after googling forever i decided i was
> only person in the Xen world not intimately familiar with this patch.

3.0.4 and xen-unstable currently come with a patched linux kernel src
for convenience (though the intention is to move this out of tree right
after 3.0.5 is released).


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