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RE: [Xen-devel] etherbridge bottleneck

To: "David Becker" <becker@xxxxxxxxxxx>, <xen-devel@xxxxxxxxxxxxxxxxxxxxx>
Subject: RE: [Xen-devel] etherbridge bottleneck
From: "Ian Pratt" <m+Ian.Pratt@xxxxxxxxxxxx>
Date: Sun, 14 Nov 2004 19:53:01 -0000
Delivery-date: Sun, 14 Nov 2004 20:23:19 +0000
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Thread-index: AcTHb2GDT9tvqMQxR5SDVCbganRLzgDDGotw
Thread-topic: [Xen-devel] etherbridge bottleneck
 > I ran some iperf tests today and it looks like the 
> etherbridge is the limiting factor on throughput.  In the 
> beforetime, I saw great
> throughput to the VMs; over 800 Mbps.   With the bridge, the numbers
> are in the 400s somewhere.
> Is this the speed I can expect from the bridge?

We've had no particular problem with the bridge code causing a
performance bottleneck -- although there appears to be a lot of code in
the forwarding path, it mostly doesn't get executed. 

However, since its easy not to have the bridge involved in your tests it
should be fairly easy to eliminate -- just don't connect the vif to the

xenU -> xenU performance isn't something we've particularly optimised,
and going via the bridge is going to be far from ideal. It would be much
better to set up a direct netfront->netback path between the two
domains.  Xend probably isn't geared up to do this right now, but it
should be possible to add. It'll probably be quite easy to add to x2d2
(new in the unstable tree) which is what we use for prototyping.

> My iperf numbers:
>  940 Mbps  stock linux -> stock linux
>  470 Mbps  stock linux -> xenU
>  533 Mbps  xenU -> stock linux 

We have no problem getting 900Mb/s in/out of xenU's and the wire on our
2.4GHz Xeon systems (regardless of whether using uniprocessor, SMP or

What do you get between the wire and domain 0? You should be getting
940Mb/s as per your stock-stock comparison. If not, sounds like there
may be an interrupt problem with Xen on your system.


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