Open Stack

On Fri, Jun 24, 2016 at 04:52:31PM +0800, Chen Fan wrote:
> 
> 
> On 2016年06月24日 16:20, Daniel P. Berrange wrote:
> > 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.
> Hi Daniel,
> 
>     sorry, I directly reference the implementation of nodedev in libvirt, in
> function
> virHostdevPreparePCIDevices :
>  257         if (pcisrc->backend == VIR_DOMAIN_HOSTDEV_PCI_BACKEND_VFIO)
>  258             virPCIDeviceSetStubDriver(pci, VIR_PCI_STUB_DRIVER_VFIO);
>  259         else if (pcisrc->backend == VIR_DOMAIN_HOSTDEV_PCI_BACKEND_XEN)
>  260             virPCIDeviceSetStubDriver(pci, VIR_PCI_STUB_DRIVER_XEN);
>  261         else
>  262             virPCIDeviceSetStubDriver(pci, VIR_PCI_STUB_DRIVER_KVM);
> 
> IIUC, the stub driver should be "legacy KVM", do we need to change the stub
> drvier
> to VIR_PCI_STUB_DRIVER_VFIO by default.

If libvirt uses VFIO, then it'll use the VFIO stub driver, which is fine.

Regards,
Daniel
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