[libvirt] qemu-kvm networking speed

Bryan_Coleman at dart.biz Bryan_Coleman at dart.biz
Fri Mar 13 18:02:15 UTC 2009

Thanks for all of the suggestions.  I am using Fedora 10 on both the host 
and guests.

One thing of note: I was previously using a realtek setup.  When I would 
do something network intensive ( nessus scan, iperf ), the network on the 
guest would just stop working.  Switching to the virtio setup everything 
works just fine.

Thanks again,


"Daniel P. Berrange" <berrange at redhat.com> 
Sent by: libvir-list-bounces at redhat.com
03/13/2009 06:13 AM
Please respond to
"Daniel P. Berrange" <berrange at redhat.com>

Bryan_Coleman at dart.biz
libvir-list at redhat.com
Re: [libvirt] qemu-kvm networking speed

On Thu, Mar 12, 2009 at 04:18:27PM -0400, Bryan_Coleman at dart.biz wrote:
> Thank you for the suggestion.  Switching to virtio and/or e1000 helped 
> still was not able to exceed 450Mb/s.  It took me awhile to figure out 
> had to either restart or reload libvirtd for the changes to take effect. 

> Is there anything else I could check/change to approach 1000Mb/s or 
> higher?

I think it really comes down to tuning of the host & guest OS at that 
and making sure you have the absolute latest KVM host side, and absolute
latest guest kernel. Early VirtIO guest drivers were not hugely optimized.
There has been alot of optimization work in .27, .28, .29 kernels getting
better all the time. Also make sure things like checksum/segmentation
offload are enabled (ethtool settings). Also things like iptables can have
impact - so worth checking how that's setup in host - eg, turn off
net.bridge.bridge-nf-call-{iptables,arptables,ip6tables} sysctl settings
to avoid having bridged traffic in host pushed up through iptables.
This isn't really my area of expertize, so you'll probably get more help
asking on the kvm development mailing list

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