[openstack-dev] [nova][pci-passthrough] definitely specify VFIO driver as the host PCI driver for passthrough

Daniel P. Berrange berrange at redhat.com
Fri Jun 24 08:20:53 UTC 2016

On Fri, Jun 24, 2016 at 12:27:57PM +0800, Chen Fan wrote:
> hi all,
>      in openstack, we can use the pci passthrough feature now, refer to
>      https://wiki.openstack.org/wiki/Pci_passthrough
>      but we can't definitely specify the host pci driver is LEGACY_KVM or
> newer VFIO,
>      new VFIO driver is more safer, and higher-performance user-space driver
>      than legacy kvm driver (pci-stub), the benefit relative to kvm
> assignment driver
>      could refer to http://lwn.net/Articles/474088/.
>      In additional, VFIO driver provides the GPU passthrough as primary card
> support.
>      I think it is more useful for further GPU passthrough support in
> openstack.
>      Openstack relies on the libvirt nodedev device configuration to do pci
> passthrough,
>      with managed mode, the configured device is automatically detached and
> re-attached
>      with KVM or VFIO driver that depended on the host driver modules
> configuration,
>      so now we can't specify the driver in openstack to VFIO mode, I think
> we should need
>      to add this feature support in openstack to get pci passhthrough more
> scalability.
>      a simply idea is to add a option in nova.conf HOST_PCI_MODEL = VFIO
> /KVM to specify
>      the pci passthrough device driver is using VFIO driver.
>      any comments are welcome. :)

I don't see any reason to add a configuration option. If the host is
capable of doing VFIO, libvirt will always aim to use VFIO in preference
to the legacy system.

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