[Xen-users] Slow network performance between HVM guests

[Martin Goldstone <m.j.goldstone@xxxxxxxxxxxxxxx>]

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 3.0.4.1 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,

Martin

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