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Tsirkin" Subject: Re: VFIO Migration Message-ID: <20201105141725.GK3186@work-vm> References: <20201103121709.GD3566@work-vm> <20201103152752.GC253848@stefanha-x1.localdomain> <20201103184951.GM3566@work-vm> <20201104073636.GB390503@stefanha-x1.localdomain> <20201104101423.GB3896@work-vm> <20201104164744.GC425016@stefanha-x1.localdomain> <20201104173202.GG3896@work-vm> <20201105114037.GC462479@stefanha-x1.localdomain> <20201105121324.GH3186@work-vm> <20201105074428-mutt-send-email-mst@kernel.org> MIME-Version: 1.0 In-Reply-To: <20201105074428-mutt-send-email-mst@kernel.org> User-Agent: Mutt/1.14.6 (2020-07-11) X-Scanned-By: MIMEDefang 2.79 on 10.5.11.12 Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=dgilbert@redhat.com X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Received-SPF: pass client-ip=63.128.21.124; envelope-from=dgilbert@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-detected-operating-system: by eggs.gnu.org: First seen = 2020/11/04 22:46:30 X-ACL-Warn: Detected OS = Linux 2.2.x-3.x [generic] [fuzzy] X-Spam_score_int: -20 X-Spam_score: -2.1 X-Spam_bar: -- X-Spam_report: (-2.1 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.001, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_NONE=-0.0001, RCVD_IN_MSPIKE_H5=0.001, RCVD_IN_MSPIKE_WL=0.001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: John G Johnson , Daniel =?iso-8859-1?Q?P=2E_Berrang=E9?= , quintela@redhat.com, Jason Wang , Felipe Franciosi , Kirti Wankhede , qemu-devel@nongnu.org, Alex Williamson , Stefan Hajnoczi , Thanos Makatos , Paolo Bonzini Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" * Michael S. Tsirkin (mst@redhat.com) wrote: > On Thu, Nov 05, 2020 at 12:13:24PM +0000, Dr. David Alan Gilbert wrote: > > * Stefan Hajnoczi (stefanha@redhat.com) wrote: > > > On Wed, Nov 04, 2020 at 05:32:02PM +0000, Dr. David Alan Gilbert wrote: > > > > * Stefan Hajnoczi (stefanha@redhat.com) wrote: > > > > > Michael replied in another sub-thread wondering if versions are really > > > > > necessary since tools do the migration checks. Let's try dropping > > > > > versions to simplify things. We can bring them back if needed later. > > > > > > > > What does a user facing tool do? If I say I want one of these NICs > > > > and I'm on the latest QEMU machine type, who sets all these parameters? > > > > > > The machine type is orthogonal since QEMU doesn't know about every > > > possible VFIO device. The device is like a PCI adapter that is added to > > > a physical machine aftermarket, it's not part of the base machine's > > > specs. > > > > OK, but ignoring migration, I think the same problem holds; if I'm a > > tool creating one of these VMs, and I plug this device in, what do I do > > with all it's configuration parameters? I'd assume most of the time > > that they don't know about or dont care about most of the parameters, > > they just want the sane defaults unless told otherwise. > > I think that if you ignore migration then you can ignore parameters. So if I ingore parameters, do I get the latest, greatest config from the device implementation I have? > > > The migration tool queries the parameters from the source device. > > > VFIO/mdev will provide sysfs attrs. For vfio-user I'm not sure whether > > > to print the parameters during device instantiation, require a > > > VFIO-compatible FUSE directory, or to use a query-migration-params RPC > > > command. > > > > But on VM creation we have to answer the question of what config do we > > want; so for example lets say I'm creating a new VM in my cluster, > > but I want to be sure that later I can migrate it. I can read the > > config off one of the other machines; can I just use that even if my > > new machine has a later device implementation? > > > > Dave > > I don't think so - we need a tool that can query a set of machines and then > produce a safe configuration. That's why I liked the 'version' idea; you just have to find the lowest version in your set. Dave > The same problem exists with vhost as well it will just > explode exponentially with lots more devices and backends ... > Talked about it a bit in my kvm forum preso ... > > > > Let's discuss this more when the next revision of the document is sent > > > out, because it modifies the approach so that migration parameters are > > > logically separate from device configuration parameters. That changes > > > things a bit. > > > > > > Stefan > > > > > > -- > > Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK > -- Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK