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[Xen-users] Slow network performance between HVM guests

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Subject: [Xen-users] Slow network performance between HVM guests
From: Martin Goldstone <m.j.goldstone@xxxxxxxxxxxxxxx>
Date: Wed, 23 May 2007 16:05:16 +0100
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Hi all,

We're running Xen 3.1 on Centos 5 here (x86_64, kernel 2.6.18), and we're seeing some odd networking issues with our Windows HVM guests. Perhaps someone here has some ideas they can offer.

Briefly, the specs of the host are: Dual Xeon 3 GHz (Dual Core + HT), 4GB RAM, 73 GB HDD. Network is e1000.

The Windows HVM guests are Windows Server 2003 R2 Standard x86-64, with 2 VCPUs, 1GB RAM, 16GB HDD (in a file), rtl8139 network.

Basically, file transfer speeds between guests (both on the same bridge) on the same host are approximately 10% (if not less) of the speed of file transfers from a HVM guest to another system (virtualised or not) away from that host. Any ideas, or is this normal behaviour? This is affecting us with Xen 3.03 and as well, so it's not just a 3.1 thing. I've disabled iptables on dom0 to see if that makes a difference (it doesn't). We've tried the 32 bit version of Windows, and we've reduced the number of VCPUs to 1, and increased to 4, all without success. We originally thought it might have something to do with another issue we were experiencing (ping times reported in Windows were very strange, show latency of several thousand ms, and showing negative latency times as well) but that issue disappeared after setting the number of VCPUs to 1 (apparently there is a bug in the Windows Multiprocessor ACPI HAL (incidentally, does anyone know if this bug affects anything other than the displayed latency times?)).

We haven't had any success tracking this down so far.  Any ideas?

Thanks in advance for any help,


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