bad KVM network performance with 10GB

[John McCabe-Dansted]

On Mon, Jul 5, 2010 at 7:12 PM, Scholte van Mast, Rene
<r.scholtevanmast at iq-optimize.de> wrote:
> Hello,
> I have trouble with the network performance inside my virtual machines.

As I understand this mailing list is for development discussion, and
people wanting support are generally invited to report the problem to
one of the support channels listed here:

http://www.ubuntu.com/support/community

Before you do that, a few things I'd check are: (VMs often have
trouble with SMP)

1) Does the problem occur when you only use a single connection on
both host and client?
2) How much CPU is used on the client? (what does top say?)
3) How many CPUs are reported in /proc/cpuinfo
3a) Does increasing the number of CPUs assigned to the client help?
3b) Alternatively, does assigning only a single CPU to the client help?

Also there is a related discussion on tuning for performance on 10GB
links with KVM
http://linux-iscsi.org/index.php/KVM-LIO-Target

Finally it is known the TX mitigation can cause problems with KVM
performance. I am not sure if this is your problem, but I'd look at
look at:
https://bugzilla.redhat.com/show_bug.cgi?id=504647
and see if disabiling TX mitigation helps.

-- 
John C. McCabe-Dansted