Re: [Qemu-devel] [RFC v2] libvirt vGPU QEMU integration

[Alex Williamson]

On Wed, 21 Sep 2016 04:10:53 +0000
"Tian, Kevin" <address@hidden> wrote:

> > From: Kirti Wankhede [mailto:address@hidden
> > Sent: Wednesday, September 21, 2016 12:23 AM
> > 
> > 
> > On 9/20/2016 8:13 PM, Alex Williamson wrote:  
> > > On Tue, 20 Sep 2016 19:51:58 +0530
> > > Kirti Wankhede <address@hidden> wrote:
> > >  
> > >> On 9/20/2016 3:06 AM, Alex Williamson wrote:  
> > >>> On Tue, 20 Sep 2016 02:05:52 +0530
> > >>> Kirti Wankhede <address@hidden> wrote:
> > >>>  
> > >>>> Hi libvirt experts,
> > >>>>
> > >>>>
> > >>>> 'create':
> > >>>>     Write-only file. Mandatory.
> > >>>>     Accepts string to create mediated device.
> > >>>>
> > >>>> 'name':
> > >>>>     Read-Only file. Mandatory.
> > >>>>     Returns string, the name of that type id.
> > >>>>
> > >>>> 'fb_length':
> > >>>>     Read-only file. Mandatory.
> > >>>>     Returns <number>{K,M,G}, size of framebuffer.  
> > >>>
> > >>> This can't be mandatory, it's only relevant to vGPU devices, vGPUs are
> > >>> just one user of mediated devices.
> > >>>  
> > >>
> > >> As per our discussion in BOF, we would define class and its attributes.
> > >> As I mentioned above these are attributes of "display" class.  
> > >
> > > Just as I didn't know here, how does libvirt know the class of a given
> > > type id?
> > >  
> > 
> > Yes, we need some way to identify the class as Daniel mentioned in his
> > suggestion. Add a file 'class' in mdev_supported_types that would return
> > the class.
> > 
> >   
> 
> 'display' class or 'gpu' class? display represents only part of GPU 
> functionalities. I assume you want to provide an unique class ID
> for each type, instead of allowing multiple classes each identifying
> a subset of controllable GPU resources (e.g. 'display', 'render', etc.)...

Not sure where you're going with this, we're not creating a programming
interface for the device, that exists through the vfio API.  I believe
the intention here is simply a user level classification for the
purpose of being able to interpret the attributes provided in a logical
way.

> for unique class ID, I once considered whether it could be directly
> inherited from class of parent device, since typically a vendor driver
> creates mdev devices using the same type as physical device. But later
> I realized one potential value of keep a class field for mdev types,
> e.g. if we want to extend mdev to FPGA which could be programmed
> as different classes of functionalities. :-)

And how do we generically determine the class of a parent device?  We
cannot assume the parent device is PCI.  Thanks,

Alex