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[Xen-users] network performance under Xen 3.3

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Subject: [Xen-users] network performance under Xen 3.3
From: "James Harper" <james.harper@xxxxxxxxxxxxxxxx>
Date: Fri, 26 Dec 2008 23:32:01 +1100
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Thread-topic: network performance under Xen 3.3
With my GPLPV drivers I was able to get a tx performance from HVM DomU
-> Dom0 of around 1-2GBits/second. That was under Xen 3.2.1 (Debian
packages). Since upgrading to Xen 3.3.0, and the latest hg as of a few
weeks ago, I can't get more than 250-300MBits/second.

Has anyone else using the GPLPV drivers observed this?

A tcpdump in Dom0 during an iperf test shows packets received from DomU
starting out at 1500 bytes, going up to about 40 kbytes (tcp large send
offload), then dropping to about 8 kbytes and staying there for the
remainder of the test. No packets are dropped, so I'm a bit puzzled as
to why this would happen. Given that Windows is doing the sending, I
assume it must be Windows making the decision on the packet size, but I
don't understand why it would be different between xen versions...


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