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

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.

- during migration, unplug the passthroughed NIC. then do native migration. - on destination side, check whether need to hotplug new NIC according to specified XML. usually, we use migrate "--xml" command option to specify the destination host NIC mac address to hotplug a new NIC, because source side passthrough NIC mac address is different, then hotplug the deivce according to the destination XML configuration.