From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:45230) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1Yuj33-0002AU-EZ for qemu-devel@nongnu.org; Tue, 19 May 2015 11:03:16 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1Yuj2z-00034u-Pl for qemu-devel@nongnu.org; Tue, 19 May 2015 11:03:13 -0400 Received: from mx1.redhat.com ([209.132.183.28]:33840) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1Yuj2z-00034p-JB for qemu-devel@nongnu.org; Tue, 19 May 2015 11:03:09 -0400 Received: from int-mx09.intmail.prod.int.phx2.redhat.com (int-mx09.intmail.prod.int.phx2.redhat.com [10.5.11.22]) by mx1.redhat.com (Postfix) with ESMTPS id 151608EB18 for ; Tue, 19 May 2015 15:03:09 +0000 (UTC) Date: Tue, 19 May 2015 16:03:04 +0100 From: "Dr. David Alan Gilbert" Message-ID: <20150519150304.GD2127@work-vm> References: <20150422092304.GE32086@redhat.com> <20150519110454-mutt-send-email-mst@redhat.com> <555B4575.1040709@redhat.com> <20150519142149.GB8535@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20150519142149.GB8535@redhat.com> Subject: Re: [Qemu-devel] [libvirt] [RFC 0/7] Live Migration with Pass-through Devices proposal List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: "Daniel P. Berrange" Cc: libvir-list@redhat.com, qemu-devel@nongnu.org, Laine Stump , "Michael S. Tsirkin" * Daniel P. Berrange (berrange@redhat.com) wrote: > On Tue, May 19, 2015 at 10:15:17AM -0400, Laine Stump wrote: > > On 05/19/2015 05:07 AM, Michael S. Tsirkin wrote: > > > On Wed, Apr 22, 2015 at 10:23:04AM +0100, Daniel P. Berrange 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. > > > There should not be a conflict. > > > guest agent should just give NM the information, and have NM do > > > the right thing. > > > > That assumes the guest will have NM running. Unless you want to severely > > limit the scope of usefulness, you also need to handle systems that have > > NM disabled, and among those the different styles of system network > > config. It gets messy very fast. > > Also OpenStack already has a way to pass guest information about the > required network setup, via cloud-init, so it would not be interested > in any thing that used the QEMU guest agent to configure network > manager. Which is really just another example of why this does not > belong anywhere in libvirt or lower. The decision to use NM is a > policy decision that will always be wrong for a non-negligble set > of use cases and as such does not belong in libvirt or QEMU. It is > the job of higher level apps to make that kind of policy decision. This is exactly my worry though; why should every higher level management system have it's own way of communicating network config for hotpluggable devices. You shoudln't need to reconfigure a VM to move it between them. This just makes it hard to move it between management layers; there needs to be some standardisation (or abstraction) of this; if libvirt isn't the place to do it, then what is? Dave > > > Users are actually asking for this functionality. > > > > > > Configuring everything manually is possible but error > > > prone. > > > > Yes, but attempting to do it automatically is also error prone (due to > > the myriad of different guest network config systems, even just within > > the seemingly narrow category of "Linux guests"). Pick your poison :-) > > Also note I'm not debating the usefulness of the overall concept > or the need for automation. It simply doesn't belong in libvirt or > lower - it is a job for the higher level management applications to > define a policy for that fits in with the way they are managing the > virtual machines and the networking. > > 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 / dgilbert@redhat.com / Manchester, UK