Re: [libvirt] [RFC v2] libvirt vGPU QEMU integration
From: Alex Williamson [mailto:alex.williamson@redhat.com]
Sent: Wednesday, September 21, 2016 12:43 PM
On Wed, 21 Sep 2016 04:10:53 +0000
"Tian, Kevin" <kevin.tian(a)intel.com> wrote:
> > From: Kirti Wankhede [mailto:kwankhede@nvidia.com]
> > 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 <kwankhede(a)nvidia.com> wrote:
> > >
> > >> On 9/20/2016 3:06 AM, Alex Williamson wrote:
> > >>> On Tue, 20 Sep 2016 02:05:52 +0530
> > >>> Kirti Wankhede <kwankhede(a)nvidia.com> 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.
I'm not against that purpose.
My main intention is that 'display' is not an accurate classification here.
If we allow classification in 'display' level, it implies more finer-grained
classifications may be further defined upon which vendor specific GPU
resources is allowed to be configured, which might be an overkill. Here
we just need a general classification like 'gpu' to cover all possible
vendor-agnostic attributes beyond display.
> 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,
Yes, this is also a good point.
Thanks
Kevin