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Re: [Xen-users] Wireless device in Xen Guest

To: James Harper <james.harper@xxxxxxxxxxxxxxxx>
Subject: Re: [Xen-users] Wireless device in Xen Guest
From: "Jui-Ting (Jerry) Weng" <jtweng@xxxxxxxxx>
Date: Tue, 25 Jan 2011 22:41:19 -0800
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I disable all offload from DomU and Dom0. To be more specific, I disable all offload on Dom0 bridge, Dom0 virtual interface, Dom0 physical interface, and DomU virtual interface. The wireless bandwidth on Xen guest is still not compariable to Xen host.

The bandwidth is tested by setting iperf client on a Xen host, and connect to the server on another laptop's Xen host or Xen guest.  When I disable all the offload, the bandwidth slightly increase on Xen host (2.2Mbps -> 2.5Mbps). However, the Xen guest still have the bandwidth at the scale of 100k bps.

Right now I'm trying to understand how long the packet stay at each interface and see where the congestion happens. But I'm curious is it a common case on Xen or I didn't setup my wireless correctly.


On Mon, Jan 24, 2011 at 7:16 PM, James Harper <james.harper@xxxxxxxxxxxxxxxx> wrote:
> I'll double check the NAT configurations.
> Right now I can use wireless in DomU. it is just incredibly slow.
> I perform the following test through Iperf.
> laptop A. Setup an Iperf server at Dom0
> (1)
> laptop B. Setup an Iperf client at Dom0, connect to laptop A.
Throughput is
> 2.2Mbps
> (2)
> laptop B. Setup an Iperf client at DomU, connect to laptop A.
Throughput is
> 90Kbps
> DomU throughput degrade to 1/20 of the Dom0. Since this only happen on
> wireless card, I was wondering if my configuration is wrong.

One thing to try is to use ethtool to disable all forms of offload in
DomU and Dom0 on the bridge, physical, and virtual interfaces. That
should at least confirm that offload is not the cause.

A simple tcpdump might show you some checksum issues (assuming you use
-s0 to grab the whole frame) but it's often hard to tell as packets can
have no checksum while on the bridge.


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