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

* 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.