Re: [libvirt] [Qemu-devel] [RFC 0/7] Live Migration with Pass-through Devices proposal

On Wed, Apr 22, 2015 at 06:01:56PM +0100, Dr. David Alan Gilbert wrote: > * Daniel P. Berrange (berrange(a)redhat.com) wrote: > > On Fri, Apr 17, 2015 at 04:53:02PM +0800, Chen Fan wrote: > > > backgrond: > > > Live migration is one of the most important features of virtualization technology. > > > With regard to recent virtualization techniques, performance of network I/O is critical. > > > Current network I/O virtualization (e.g. Para-virtualized I/O, VMDq) has a significant > > > performance gap with native network I/O. Pass-through network devices have near > > > native performance, however, they have thus far prevented live migration. No existing > > > methods solve the problem of live migration with pass-through devices perfectly. > > > > > > There was an idea to solve the problem in website: > > > https://www.kernel.org/doc/ols/2008/ols2008v2-pages-261-267.pdf > > > Please refer to above document for detailed information. > > > > > > So I think this problem maybe could be solved by using the combination of existing > > > technology. and the following steps are we considering to implement: > > > > > > - before boot VM, we anticipate to specify two NICs for creating bonding device > > > (one plugged and one virtual NIC) in XML. here we can specify the NIC's mac addresses > > > in XML, which could facilitate qemu-guest-agent to find the network interfaces in guest. > > > > > > - when qemu-guest-agent startup in guest it would send a notification to libvirt, > > > then libvirt will call the previous registered initialize callbacks. so through > > > the callback functions, we can create the bonding device according to the XML > > > configuration. and here we use netcf tool which can facilitate to create bonding device > > > easily. > > > > I'm not really clear on why libvirt/guest agent needs to be involved in this. > > I think configuration of networking is really something that must be left to > > the guest OS admin to control. I don't think the guest agent should be trying > > to reconfigure guest networking itself, as that is inevitably going to conflict > > with configuration attempted by things in the guest like NetworkManager or > > systemd-networkd. > > > > IOW, if you want to do this setup where the guest is given multiple NICs connected > > to the same host LAN, then I think we should just let the gues admin configure > > bonding in whatever manner they decide is best for their OS install. > > I disagree; there should be a way for the admin not to have to do this manually; > however it should interact well with existing management stuff. > > At the simplest, something that marks the two NICs in a discoverable way > so that they can be seen that they're part of a set; with just that ID system > then an installer or setup tool can notice them and offer to put them into > a bond automatically; I'd assume it would be possible to add a rule somewhere > that said anything with the same ID would automatically be added to the bond. I didn't mean the admin would literally configure stuff manually. I really just meant that the guest OS itself should decide how it is done, whether NetworkManager magically does the right thing, or the person building the cloud disk image provides a magic udev rule, or $something else. I just don't think that the QEMU guest agent should be involved, as that will definitely trample all over other things that manage networking in the guest.

I could see this being solved in the cloud disk images by using cloud-init metadata to mark the NICs as being in a set, or perhaps there is some magic you could define in SMBIOS tables, or something else again. A cloud-init based solution wouldn't need any QEMU work, but an SMBIOS solution might.

Regards, Daniel -- |: http://berrange.com -o- http://www.flickr.com/photos/dberrange/ :| |: http://libvirt.org -o- http://virt-manager.org :| |: http://autobuild.org -o- http://search.cpan.org/~danberr/ :| |: http://entangle-photo.org -o- http://live.gnome.org/gtk-vnc :|