Using ports vnic_type=’vdpa’
23.0.0 (Wallaby)
Introduced support for vDPA.
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 <admin/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-vmvDPA 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.