* Daniel P. Berrange (berra...@redhat.com) wrote: > On Wed, Apr 22, 2015 at 06:12:25PM +0100, Dr. David Alan Gilbert wrote: > > * Daniel P. Berrange (berra...@redhat.com) wrote: > > > On Wed, Apr 22, 2015 at 06:01:56PM +0100, Dr. David Alan Gilbert wrote: > > > > * Daniel P. Berrange (berra...@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. > > > > OK, good, that's about the same level I was at. > > > > > 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. > > > > Would either of these work with hotplug though? I guess as the VM starts > > off with the pair of NICs, then when you remove one and add it back after > > migration then you don't need any more information added; so yes > > cloud-init or SMBIOS would do it. (I was thinking SMBIOS stuff > > in the way that you get device/slot numbering that NIC naming is sometimes > > based > > off). > > > > What about if we hot-add a new NIC later on (not during migration); > > a normal hot-add of a NIC now turns into a hot-add of two new NICs; how > > do we pass the information at hot-add time to provide that? > > Hmm, yes, actually hotplug would be a problem with that. > > A even simpler idea would be to just keep things real dumb and simply > use the same MAC address for both NICs. Once you put them in a bond > device, the kernel will be copying the MAC address of the first NIC > into the second NIC anyway, so unless I'm missing something, we might > as well just use the same MAC address for both right away. That makes > it easy for guest to discover NICs in the same set and works with > hotplug trivially.
I bet you need to distinguish the two NICs though; you'd want the bond to send all the traffic through the real NIC during normal use; and how does the guest know when it sees the hotplug of the 1st NIC in the pair that this is a special NIC that it's about to see it's sibbling arrive. Dave > > 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 :| -- Dr. David Alan Gilbert / dgilb...@redhat.com / Manchester, UK
