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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 13:43:09 -0000
  • Delivery-date: Tue, 06 Feb 2007 05:43:23 -0800
  • List-id: Xen developer discussion <xen-devel.lists.xensource.com>
  • Thread-index: AcdJhkiDHtoPengTRcuS+RXt1NBGFQAbVvrg
  • Thread-topic: [Xen-devel] vif interface dropping 80% packets

> I'm trying to characterize the performance of 10G ethernet to a user
> domain.
> The machine has 2 configured ethernet cards, eth0 is a 1G card, and
eth2 is
> a 10G card.  (eth1 is another 1G card and eth3 is another 10G, but
> are not configured)
> I have network bridge set up on eth2 with defaults, nothing special,
>    /etc/xen/scripts/network-bridge start vifnum=2
> I have a user domain that attaches eth1 to this vif, and when I try
> tests, I get tons of packet loss in the vif interface.
> As can be seen above, vif3.1 drops about 80% of the packets it should
> transmit.  Is this expected due to something in the dom0 -> domU
> just not being able to keep up, or is there something I can do about
> It almost looks like the dom0->domU link is throttled at about 1Gb/s.
> say this because the 10G link is running about 50-60% capacity when
> drop rate is 80%.

First off, try switching to 3.0.4 and use the included 2.6.16-xen

How are you measuring the bandwidth? It's much more realistic to use TCP
as open-loop UDP blasts aren't used by any real protocols. 

> Everything has MTU 1500, btw - I noticed that Xen is pretty unhappy
with an
> MTU of 9000.

In what way?  I'd expect larger MTUs to work OK, though I haven't tested
them myself.

Does the larger MTU work in dom0, but not through to other domU's?

You may need to set the MTU on the bridge and all vif's.


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