From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:43023) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1aVaBq-0008Gb-Ok for qemu-devel@nongnu.org; Tue, 16 Feb 2016 02:36:55 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1aVaBm-0006kt-Mo for qemu-devel@nongnu.org; Tue, 16 Feb 2016 02:36:54 -0500 Received: from hqemgate16.nvidia.com ([216.228.121.65]:4420) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1aVaBm-0006kn-ER for qemu-devel@nongnu.org; Tue, 16 Feb 2016 02:36:50 -0500 Date: Mon, 15 Feb 2016 23:36:47 -0800 From: Neo Jia Message-ID: <20160216073647.GB6867@nvidia.com> References: <20160202081312.GA9895@nvidia.com> <20160202083114.GB9895@nvidia.com> <1454433079.30910.3.camel@redhat.com> <1454488111.4967.39.camel@redhat.com> <1454527963.18969.8.camel@redhat.com> <20160216071304.GA6867@nvidia.com> MIME-Version: 1.0 Content-Type: text/plain; charset="iso-8859-1" Content-Disposition: inline Content-Transfer-Encoding: quoted-printable In-Reply-To: Subject: Re: [Qemu-devel] [RFC PATCH v1 1/1] vGPU core driver : to provide common interface for vGPU. List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: "Tian, Kevin" Cc: "Ruan, Shuai" , "Song, Jike" , "kvm@vger.kernel.org" , Kirti Wankhede , qemu-devel , Alex Williamson , Gerd Hoffmann , Paolo Bonzini , "Lv, Zhiyuan" On Tue, Feb 16, 2016 at 07:27:09AM +0000, Tian, Kevin wrote: > > From: Neo Jia [mailto:cjia@nvidia.com] > > Sent: Tuesday, February 16, 2016 3:13 PM > >=20 > > On Tue, Feb 16, 2016 at 06:49:30AM +0000, Tian, Kevin wrote: > > > > From: Alex Williamson [mailto:alex.williamson@redhat.com] > > > > Sent: Thursday, February 04, 2016 3:33 AM > > > > > > > > On Wed, 2016-02-03 at 09:28 +0100, Gerd Hoffmann wrote: > > > > > =A0 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 vi= a > > > > > monitor ("info uuid") to figure what the uuid is.=A0=A0It is also= in the > > > > > smbios tables so the guest can see it in the system information t= able. > > > > > > > > > > The uuid is not visible to the kernel though, the kvm kernel driv= er > > > > > doesn't know what the uuid is (and neither does vfio).=A0=A0qemu = uses file > > > > > handles to talk to both kvm and vfio.=A0=A0qemu 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 fro= m > > > > 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 i= s > > > > started.=A0=A0Using the VM UUID then gives them a way to associate = that > > > > userspace process with a VM instance.=A0=A0Maybe 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/.=A0=A0 can be a uuid = if you want > > > > > have it that way, but it could be pretty much anything.=A0=A0The = sysfs node > > > > > will probably show up as-is in the libvirt xml when assign a vgpu= to a > > > > > vm.=A0=A0So 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, th= at's > > > > probably where we diverge from the SR-IOV model.=A0=A0SR-IOV cannot > > > > dynamically add a new VF, it needs to reset the number of VFs to ze= ro, > > > > then re-allocate all of them up to the new desired count.=A0=A0That= has some > > > > obvious implications.=A0=A0I think with both vendors here, we can > > > > dynamically allocate new vGPUs, so I would expect that libvirt woul= d > > > > create each vGPU instance as it's needed.=A0=A0None would be create= d 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.=A0=A0Having 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.=A0=A0Thanks, > > > > > > > > > > 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. > >=20 > > Hi Kevin, > >=20 > > Happy Chinese New Year! > >=20 > > I think having UUID as the vgpu device name will allow us to have an gp= u vendor > > agnostic solution for the upper layer software stack such as QEMU, who = is > > supposed to open the device. > >=20 >=20 > Qemu can use whatever sysfs path provided to open the device, regardless > of whether there is an UUID within the path... >=20 Hi Kevin, Then it will provide even more benefit of using UUID as libvirt can be implemented as gpu vendor agnostic, right? :-) The UUID can be VM UUID or vGPU group object UUID which really depends on t= he high level software stack, again the benefit is gpu vendor agnostic. Thanks, Neo > Thanks > Kevin