Re: [libvirt] [RFC PATCH 0/2] Add new mdev type for aggregated resources

[Alex Williamson <alex.williamson@redhat.com>]

On Thu, 21 Jun 2018 19:57:38 +0530
Kirti Wankhede <kwankhede@nvidia.com> wrote:

> On 6/20/2018 1:10 PM, Zhenyu Wang wrote:
> > Current mdev device create interface depends on fixed mdev type, which get uuid
> > from user to create instance of mdev device. If user wants to use customized
> > number of resource for mdev device, then only can create new mdev type for that
> > which may not be flexible.
> > 
> > To allow to create user defined resources for mdev, this RFC trys
> > to extend mdev create interface by adding new "instances=xxx" parameter
> > following uuid, for target mdev type if aggregation is supported, it can
> > create new mdev device which contains resources combined by number of
> > instances, e.g
> > 
> >     echo "<uuid>,instances=10" > create  
> 
> This seems orthogonal to the way mdev types are meant to be used. Vendor
> driver can provide the possible types to provide flexibility to the users.

I think the goal here is to define how we create a type that supports
arbitrary combinations of resources where the total number of those
resources my be sufficiently large that the parent driver enumerating
them all is not feasible.

> Secondly, not always all resources defined for a particular mdev type
> can be multiplied, for example, a mdev type for vGPU that supports 2
> heads, that can't be multiplied to use with 20 heads.

Not all types need to define themselves this way, aiui this is an
optional extension.  Userspace can determine if this feature is
available with the new attribute and if they're not aware of the new
attribute, we operate in a backwards compatible mode where 'echo $UUID >
create' consumes one instance of that type.  Mdev, like vfio, is device
agnostic, so while a vGPU example may have scaling issues that need to
be ironed out to implement this, those don't immediately negate the
value of this proposal.  Thanks,

Alex

> > VM manager e.g libvirt can check mdev type with "aggregation" attribute
> > which can support this setting. And new sysfs attribute "instances" is
> > created for each mdev device to show allocated number. Default number
> > of 1 or no "instances" file can be used for compatibility check.
> > 
> > This RFC trys to create new KVMGT type with minimal vGPU resources which
> > can be combined with "instances=x" setting to allocate for user wanted resources.
> > 
> > Zhenyu Wang (2):
> >   vfio/mdev: Add new instances parameters for mdev create
> >   drm/i915/gvt: Add new aggregation type
> > 
> >  drivers/gpu/drm/i915/gvt/gvt.c   | 26 ++++++++++++---
> >  drivers/gpu/drm/i915/gvt/gvt.h   | 14 +++++---
> >  drivers/gpu/drm/i915/gvt/kvmgt.c |  9 +++--
> >  drivers/gpu/drm/i915/gvt/vgpu.c  | 56 ++++++++++++++++++++++++++++----
> >  drivers/s390/cio/vfio_ccw_ops.c  |  3 +-
> >  drivers/vfio/mdev/mdev_core.c    | 11 ++++---
> >  drivers/vfio/mdev/mdev_private.h |  6 +++-
> >  drivers/vfio/mdev/mdev_sysfs.c   | 42 ++++++++++++++++++++----
> >  include/linux/mdev.h             |  3 +-
> >  samples/vfio-mdev/mbochs.c       |  3 +-
> >  samples/vfio-mdev/mdpy.c         |  3 +-
> >  samples/vfio-mdev/mtty.c         |  3 +-
> >  12 files changed, 141 insertions(+), 38 deletions(-)
> >