Re: [libvirt] [RFC v2] libvirt vGPU QEMU integration

On Thu, Sep 22, 2016 at 03:26:38PM +0100, Daniel P. Berrange wrote: > On Thu, Sep 22, 2016 at 08:19:21AM -0600, Alex Williamson wrote: > > On Thu, 22 Sep 2016 09:41:20 +0530 > > Kirti Wankhede <kwankhede(a)nvidia.com&gt; wrote: > > > > > >>>>> My concern is that a type id seems arbitrary but we're specifying that > > > >>>>> it be unique. We already have something unique, the name. So why try > > > >>>>> to make the type id unique as well? A vendor can accidentally create > > > >>>>> their vendor driver so that a given name means something very > > > >>>>> specific. On the other hand they need to be extremely deliberate to > > > >>>>> coordinate that a type id means a unique thing across all their product > > > >>>>> lines. > > > >>>>> > > > >>>> > > > >>>> Let me clarify, type id should be unique in the list of > > > >>>> mdev_supported_types. You can't have 2 directories in with same name. > > > >>> > > > >>> Of course, but does that mean it's only unique to the machine I'm > > > >>> currently running on? Let's say I have a Tesla P100 on my system and > > > >>> type-id 11 is named "GRID-M60-0B". At some point in the future I > > > >>> replace the Tesla P100 with a Q1000 (made up). Is type-id 11 on that > > > >>> new card still going to be a "GRID-M60-0B"? If not then we've based > > > >>> our XML on the wrong attribute. If the new device does not support > > > >>> "GRID-M60-0B" then we should generate an error, not simply initialize > > > >>> whatever type-id 11 happens to be on this new card. > > > >>> > > > >> > > > >> If there are 2 M60 in the system then you would find '11' type directory > > > >> in mdev_supported_types of both M60. If you have P100, '11' type would > > > >> not be there in its mdev_supported_types, it will have different types. > > > >> > > > >> For example, if you replace M60 with P100, but XML is not updated. XML > > > >> have type '11'. When libvirt would try to create mdev device, libvirt > > > >> would have to find 'create' file in sysfs in following directory format: > > > >> > > > >> --- mdev_supported_types > > > >> |-- 11 > > > >> | |-- create > > > >> > > > >> but now for P100, '11' directory is not there, so libvirt should throw > > > >> error on not able to find '11' directory. > > > > > > > > This really seems like an accident waiting to happen. What happens > > > > when the user replaces their M60 with an Intel XYZ device that happens > > > > to expose a type 11 mdev class gpu device? How is libvirt supposed to > > > > know that the XML used to refer to a GRID-M60-0B and now it's an > > > > INTEL-IGD-XYZ? Doesn't basing the XML entry on the name and removing > > > > yet another arbitrary requirement that we have some sort of globally > > > > unique type-id database make a lot of sense? The same issue applies > > > > for simple debug-ability, if I'm reviewing the XML for a domain and the > > > > name is the primary index for the mdev device, I know what it is. > > > > Seeing type-id='11' is meaningless. > > > > > > > > > > Let me clarify again, type '11' is a string that vendor driver would > > > define (see my previous reply below) it could be "11" or "GRID-M60-0B". > > > If 2 vendors used same string we can't control that. right? > > > > > > > > > >>>> Lets remove 'id' from type id in XML if that is the concern. Supported > > > >>>> types is going to be defined by vendor driver, so let vendor driver > > > >>>> decide what to use for directory name and same should be used in device > > > >>>> xml file, it could be '11' or "GRID M60-0B": > > > >>>> > > > >>>> <device> > > > >>>> <name>my-vgpu</name> > > > >>>> <parent>pci_0000_86_00_0</parent> > > > >>>> <capability type='mdev'> > > > >>>> <type='11'/> > > > >>>> ... > > > >>>> </capability> > > > >>>> </device> > > > > Then let's get rid of the 'name' attribute and let the sysfs directory > > simply be the name. Then we can get rid of 'type' altogether so we > > don't have this '11' vs 'GRID-M60-0B' issue. Thanks, > > That sounds nice to me - we don't need two unique identifiers if > one will do. Hi Alex and Daniel, I just had some internal discussions here within NVIDIA and found out that actually the name/label potentially might not be unique and the "id" will be. So I think we still would like to keep both so the id is the programmatic id and the name/label is a human readable string for it, which might get changed to be non-unique by outside of engineering.