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

>>>>> 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>