> From: Neo Jia [mailto:c...@nvidia.com] > Sent: Tuesday, February 16, 2016 3:13 PM > > On Tue, Feb 16, 2016 at 06:49:30AM +0000, Tian, Kevin wrote: > > > From: Alex Williamson [mailto:alex.william...@redhat.com] > > > Sent: Thursday, February 04, 2016 3:33 AM > > > > > > On Wed, 2016-02-03 at 09:28 +0100, Gerd Hoffmann wrote: > > > > Hi, > > > > > > > > > Actually I have a long puzzle in this area. Definitely libvirt will > > > > > use UUID to > > > > > mark a VM. And obviously UUID is not recorded within KVM. Then how > > > > > does > > > > > libvirt talk to KVM based on UUID? It could be a good reference to > > > > > this design. > > > > > > > > libvirt keeps track which qemu instance belongs to which vm. > > > > qemu also gets started with "-uuid ...", so one can query qemu via > > > > monitor ("info uuid") to figure what the uuid is. It is also in the > > > > smbios tables so the guest can see it in the system information table. > > > > > > > > The uuid is not visible to the kernel though, the kvm kernel driver > > > > doesn't know what the uuid is (and neither does vfio). qemu uses file > > > > handles to talk to both kvm and vfio. qemu notifies both kvm and vfio > > > > about anything relevant events (guest address space changes etc) and > > > > connects file descriptors (eventfd -> irqfd). > > > > > > I think the original link to using a VM UUID for the vGPU comes from > > > NVIDIA having a userspace component which might get launched from a udev > > > event as the vGPU is created or the set of vGPUs within that UUID is > > > started. Using the VM UUID then gives them a way to associate that > > > userspace process with a VM instance. Maybe it could register with > > > libvirt for some sort of service provided for the VM, I don't know. > > > > Intel doesn't have this requirement. It should be enough as long as > > libvirt maintains which sysfs vgpu node is associated to a VM UUID. > > > > > > > > > qemu needs a sysfs node as handle to the vfio device, something > > > > like /sys/devices/virtual/vgpu/<name>. <name> can be a uuid if you want > > > > have it that way, but it could be pretty much anything. The sysfs node > > > > will probably show up as-is in the libvirt xml when assign a vgpu to a > > > > vm. So the name should be something stable (i.e. when using a uuid as > > > > name you should better not generate a new one on each boot). > > > > > > Actually I don't think there's really a persistent naming issue, that's > > > probably where we diverge from the SR-IOV model. SR-IOV cannot > > > dynamically add a new VF, it needs to reset the number of VFs to zero, > > > then re-allocate all of them up to the new desired count. That has some > > > obvious implications. I think with both vendors here, we can > > > dynamically allocate new vGPUs, so I would expect that libvirt would > > > create each vGPU instance as it's needed. None would be created by > > > default without user interaction. > > > > > > Personally I think using a UUID makes sense, but it needs to be > > > userspace policy whether that UUID has any implicit meaning like > > > matching the VM UUID. Having an index within a UUID bothers me a bit, > > > but it doesn't seem like too much of a concession to enable the use case > > > that NVIDIA is trying to achieve. Thanks, > > > > > > > I would prefer to making UUID an optional parameter, while not tieing > > sysfs vgpu naming to UUID. This would be more flexible to different > > scenarios where UUID might not be required. > > Hi Kevin, > > Happy Chinese New Year! > > I think having UUID as the vgpu device name will allow us to have an gpu > vendor > agnostic solution for the upper layer software stack such as QEMU, who is > supposed to open the device. >
Qemu can use whatever sysfs path provided to open the device, regardless of whether there is an UUID within the path... Thanks Kevin
