[openstack-dev] vGPUs support for Nova - Implementation

Sahid Orentino Ferdjaoui sferdjao at redhat.com
Fri Sep 29 15:41:15 UTC 2017

On Fri, Sep 29, 2017 at 12:26:07PM +0000, Bob Ball wrote:
> Hi Sahid,
> > Please consider the support of MDEV for the /pci framework which provides support for vGPUs [0].

> From my understanding, this MDEV implementation for vGPU would be
> entirely specific to libvirt, is that correct?

No, but Linux specific yes. Windows is supporting SR-IOV.

> XenServer's implementation for vGPU is based on a pooled device
> model (as described in
> http://lists.openstack.org/pipermail/openstack-dev/2017-September/122702.html)

This topic is referring something which I guess everyone understand
now - It's basically why I do have added support of MDEV in /pci to
make it working whatever how the virtual devices are exposed, SR-IOV
or MDEV.

> 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

> I'm not familiar with mdev, but it looks Linux specific, so would not be usable by Hyper-V?
> I've also not been able to find suggestions that VMWare can make use of mdev, although I don't know the architecture of VMWare's integration.
> The concepts of PCI and SR-IOV are, of course, generic, but I think out of principal we should avoid a hypervisor-specific integration for vGPU (indeed Citrix has been clear from the beginning that the vGPU integration we are proposing is intentionally hypervisor agnostic)
> I also think there is value in exposing vGPU in a generic way, irrespective of the underlying implementation (whether it is DEMU, mdev, SR-IOV or whatever approach Hyper-V/VMWare use).
> It's quite difficult for me to see how this will work for other
> hypervisors.  Do you also have a draft alternate spec where more
> details can be discussed?

I would expect that XenServer provides the MDEV UUID, then it's easy
to ask sysfs if you need to get the NUMA node of the physical device
or the mdev_type.

> Bob
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