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

[Zhenyu Wang]

On 2018.06.21 09:00:28 -0600, Alex Williamson wrote:
> On Thu, 21 Jun 2018 19:57:38 +0530
> Kirti Wankhede <kwankhede at 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.

yeah, for vGPU we actually can have flexible config for memory size but
currently fixed by type definition. Although like for display config, we
are just sticking with 1 head config even for aggregate type.

> 
> 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,
> 

yep, backward compatible is always ensured by this, so for no
aggregation attrib type, still keep current behavior, driver should
refuse "instances=" if set by user. One thing I'm concern is that
looks currently without changing mdev create ops interface, can't
carry that option for driver, or should we do with more general parameter?

thanks

> 
> > > 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(-)
> > >   
> 

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