[openstack-dev] vGPUs support for Nova - Implementation

Sahid Orentino Ferdjaoui sferdjao at redhat.com
Mon Oct 2 14:35:26 UTC 2017

On Fri, Sep 29, 2017 at 04:51:10PM +0000, Bob Ball wrote:
> Hi Sahid,
> > > a second device emulator along-side QEMU.  There is no mdev 
> > > integration.  I'm concerned about how much mdev-specific functionality 
> > > would have to be faked up in the XenServer-specific driver for vGPU to 
> > > be used in this way.
> >
> > What you are refering with your DEMU it's what QEMU/KVM have with its vfio-pci. XenServer is
> > reading through MDEV since the vendors provide drivers on *Linux* using the MDEV framework.
> > MDEV is a kernel layer, used to expose hardwares, it's not hypervisor specific.
> It is possible that the vendor's userspace libraries use mdev,
> however DEMU has no concept of mdev at all.  If the vendor's
> userspace libraries do use mdev then this is entirely abstracted
> from XenServer's integration.  While I don't have access to the
> vendors source for the userspace libraries or the kernel module my
> understanding was that the kernel module in XenServer's integration
> is for the userspace libraries to talk to the kernel module and for
> IOCTLS.  My reading of mdev implies that /sys/class/mdev_bus should
> exist for it to be used?  It does not exist in XenServer, which to
> me implies that the vendor's driver for XenServer do not use mdev?

I shared our discussion to Alex Williamson, it's response:

> Hi Sahid,
> XenServer does not use mdev for vGPU support.  The mdev/vfio
> infrastructure was developed in response to DEMU used on XenServer,
> which we felt was not an upstream acceptable solution.  There has
> been cursory interest in porting vfio to Xen, so it's possible that
> they might use the same mechanism some day, but for now they are
> different solutions, the vifo/mdev solution being the only one
> accepted upstream so far. Thanks,
> Alex

It's my mistake. It seems clear now that XenSever can't take the
benefice of that mdev support I have added in /pci module. The support
of vGPUs for Xen will have to wait for the generic device management I

> Bob
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