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.
However, I agree that you might be able to avoid having to do anything in the
guest agent.
Dave
--
Dr. David Alan Gilbert / dgilbert(a)redhat.com / Manchester, UK