RE: [PATCH v6 00/20] Add VFIO mediated device support and DEV-MSI support for the idxd driver

[Tian, Kevin]

> From: Jason Gunthorpe <jgg@xxxxxxxxxx>
> Sent: Thursday, June 3, 2021 7:18 AM
> 
> On Wed, Jun 02, 2021 at 08:40:51AM -0700, Dave Jiang wrote:
> >
> > On 5/23/2021 4:22 PM, Jason Gunthorpe wrote:
> > > On Fri, May 21, 2021 at 05:19:05PM -0700, Dave Jiang wrote:
> > > > Introducing mdev types “1dwq-v1” type. This mdev type allows
> > > > allocation of a single dedicated wq from available dedicated wqs. After
> > > > a workqueue (wq) is enabled, the user will generate an uuid. On mdev
> > > > creation, the mdev driver code will find a dwq depending on the mdev
> > > > type. When the create operation is successful, the user generated uuid
> > > > can be passed to qemu. When the guest boots up, it should discover a
> > > > DSA device when doing PCI discovery.
> > > >
> > > > For example of “1dwq-v1” type:
> > > > 1. Enable wq with “mdev” wq type
> > > > 2. A user generated uuid.
> > > > 3. The uuid is written to the mdev class sysfs path:
> > > > echo $UUID >
> /sys/class/mdev_bus/0000\:00\:0a.0/mdev_supported_types/idxd-1dwq-
> v1/create
> > > > 4. Pass the following parameter to qemu:
> > > > "-device vfio-pci,sysfsdev=/sys/bus/pci/devices/0000:00:0a.0/$UUID"
> > > So the idxd core driver knows to create a "vfio" wq with its own much
> > > machinery but you still want to involve the horrible mdev guid stuff?
> > >
> > > Why??
> >
> > Are you referring to calling mdev_device_create() directly in the mdev
> > idxd_driver probe?
> 
> No, just call vfio_register_group_dev and forget about mdev.
> 
> > I think this would work with our dedicated wq where a single mdev
> > can be assigned to a wq.
> 
> Ok, sounds great
> 
> > However, later on when we need to support shared wq where we can
> > create multiple mdev per wq, we'll need an entry point to do so. In
> > the name of making things consistent from user perspective, going
> > through sysfs seems the way to do it.
> 
> Why not use your already very complicated idxd sysfs to do this?
> 

Jason, can you clarify your attitude on mdev guid stuff? Are you 
completely against it or case-by-case? If the former, this is a big
decision thus it's better to have consensus with Alex/Kirti. If the
latter, would like to hear your criteria for when it can be used
and when not...

Thanks
Kevin