Re: [libvirt-users] How can a bridge be optimized?
On Mon, Jun 11, 2012 at 07:22:48PM +0300, Henrik Ahlgren wrote:
On 06/11/2012 06:34 PM, Whit Blauvelt wrote:
> Looking into background info on these, it looks like SR-IOV capability is
> specific to certain NICs and not documented for KVM/libvirt in any obvious
> place. Maybe I just didn't find it.
I think SR-IOV is more for high-end 10 GigE networks; with 1 GigE NICs
and fairly modern hardware you should get decent performance (almost
wire-speed) with just simple virtio + bridge setup.
Also, make sure you have the vhost_net module loaded (or kernel compiled
with CONFIG_VHOST_NET=y), recent (0.9.0 and newer I believe?) libvirt
versions should detect it and enable vhost=on with QEMU/KVM
automatically. That should give you some further performance boost.
I agree that there is some room for improvement in libvirt documentation
regarding the network configuration.
Thanks. Not sure if I have the invocation or prerequisites right. If I do
<interface type='bridge'>
<mac address='00:16:36:89:65:2e'/>
<source bridge='br0'/>
<address type='pci' domain='0x0000' bus='0x00'
slot='0x03' function='0x0'/>
<model type='virtio'/>
</interface>
I get around 150Mb, (on a Gb interface). But then its still showing as
"-device rtl8139" on the host. Should that be? What are the minimum versions
of stuff for virtio to work for this? Virtio's getting passed through for
memballoon (from XML in the form "<memballoon model='virtio'>") so
it's
there.
If I take out that "address type" line throughput drops to around 100Mb. I
do have vhost_net loaded now on the host (didn't before). Another VM on the
same host with no virtio line tests even slower.
So far in our instance slow hasn't been bad. The VMs haven't needed more for
their purposes. But now we're wanting to run a few where IO requirements are
higher, thus my interest in tuning this.
Whit