Using ports vnic_type=’vdpa’

Added in version 23.0.0: (Wallaby)

Introduced support for vDPA.

Added in version 26.0.0: (Zed)

Added support for all instance move operations, and the interface attach/detach, and suspend/resume operations.

Important

The functionality described below is only supported by the libvirt/KVM virt driver.

The kernel vDPA (virtio Data Path Acceleration) framework provides a vendor independent framework for offloading data-plane processing to software or hardware virtio device backends. While the kernel vDPA framework supports many types of vDPA devices, at this time nova only support virtio-net devices using the vhost-vdpa front-end driver. Support for virtio-blk or virtio-gpu may be added in the future but is not currently planned for any specific release.

vDPA device tracking

When implementing support for vDPA based neutron ports one of the first decisions nova had to make was how to model the availability of vDPA devices and the capability to virtualize vDPA devices. As the initial use-case for this technology was to offload networking to hardware offload OVS via neutron ports the decision was made to extend the existing PCI tracker that is used for SR-IOV and pci-passthrough to support vDPA devices. As a result a simplification was made to assume that the parent device of a vDPA device is an SR-IOV Virtual Function (VF). As a result software only vDPA device such as those created by the kernel vdpa-sim sample module are not supported.

To make vDPA device available to be scheduled to guests the operator should include the device using the PCI address or vendor ID and product ID of the parent VF in the PCI device_spec. See: pci-passthrough for details.

Nova will not create the VFs or vDPA devices automatically. It is expected that the operator will allocate them before starting the nova-compute agent. While no specific mechanisms is prescribed to do this udev rules or systemd service files are generally the recommended approach to ensure the devices are created consistently across reboots.

Note

As vDPA is an offload only for the data plane and not the control plane a vDPA control plane is required to properly support vDPA device passthrough. At the time of writing only hardware offloaded OVS is supported when using vDPA with nova. Because of this vDPA devices cannot be requested using the PCI alias. While nova could allow vDPA devices to be requested by the flavor using a PCI alias we would not be able to correctly configure the device as there would be no suitable control plane. For this reason vDPA devices are currently only consumable via neutron ports.

Virt driver support

Supporting neutron ports with vnic_type=vdpa depends on the capability of the virt driver. At this time only the libvirt virt driver with KVM is fully supported. QEMU may also work but is untested.

vDPA support depends on kernel 5.7+, Libvirt 6.9.0+ and QEMU 5.1+.

vDPA lifecycle operations

To boot a VM with vDPA ports they must first be created in neutron. To do this the normal SR-IOV workflow is used where by the port is first created in neutron and passed into nova as part of the server create request.

openstack port create --network <my network> --vnic-type vdpa vdpa-port
openstack server create --flavor <my-flavor> --image <my-image> --port <vdpa-port uuid> vdpa-vm

vDPA live migration

At this time QEMU and the vhost-vdpa kernel module do not support transparent live migration of vm with vdpa ports. To enable live migration of VMs with vDPA interfaces the existing SR-IOV hotplug live migration procedure has been extended to include vnic_type='vdpa' interfaces.