On Thu, Dec 17, 2009 at 07:28:00AM -0600, Anthony Liguori wrote:
Daniel P. Berrange wrote:
The more interesting invocation of vhost-net though is one where the vhost-net device backs directly to a physical network card. In this mode, vhost should get considerably better performance than the current implementation. I don't know the syntax yet, but I think it's reasonable to assume that it will look something like -net tap,dev=eth0. The effect will be that eth0 is dedicated to the guest.
Ok, so in this model you have to create a dedicated ethXX device for every guest, no sharing ?
Yup. You may be sharing a physical network device via SR-IOV, but from libvirt's perspective, we're dedicating a physical device to a guest virtual nic.
I think there are a few ways libvirt could support vhost-net in this second mode. The simplest would be to introduce a new tag similar to <source network='br0'>. In fact, if you probed the device type for the network parameter, you could probably do something like <source network='eth0'> and have it Just Work.
Another model would be to have libvirt see an SR-IOV adapter as a network pool whereas it handled all of the VF management. Considering how inflexible SR-IOV is today, I'm not sure whether this is the best model.
Agreed, given the hardware limitations I don't see that it is worth the bother.
This new mode is not really what we'd call 'bridging' in libvirt network XML format, so I think we'll want to define a new type of network config for it in libvirt. Perhaps
<network type='physical'> <source dev='eth0'/> </network>
Opps, when i write <network> here I actually mean <interface>
Or type='passthru'
That certainly simplifies the problem.
I don't know whether SR-IOV requires additional setup though wrt programming the VF's mac address. It may make sense for libvirt to at least do that.
Oh sure, that's easy enough - if there's no MAC in the XML we autogenerate one anyway, so we always have a mac for every interface & do whatever is needed with that. Daniel -- |: Red Hat, Engineering, London -o- http://people.redhat.com/berrange/ :| |: http://libvirt.org -o- http://virt-manager.org -o- http://ovirt.org :| |: http://autobuild.org -o- http://search.cpan.org/~danberr/ :| |: GnuPG: 7D3B9505 -o- F3C9 553F A1DA 4AC2 5648 23C1 B3DF F742 7D3B 9505 :|