Enable SR-IOV NIC offload feature discovery


Today, most networking hardware vendors implement some of the TCP/IP stack, traditionally done by the host operating system, in the NIC. Offloading some of these functions to dedicated hardware frees up CPU cycles for applications running on the system.

libvirt implemented the SR-IOV NIC offload feature discovery in version 1.2.14 [1].

Problem description

NIC features, in particular features around various hardware offload, are useful for network-intensive applications. Unfortunately, Nova doesn’t yet retrieve physical NIC information from the system, which means the scheduler cannot filter out compute hosts that do not contain certain NIC features.

If a virtual machine, during the booting step, discovers a NIC offload feature, Nova Scheduler can select those hosts that have PCI devices with that feature.

The aim of this spec is to fill this gap by proposing a method to read this information, store it, use it during the scheduling process and provide a way to share this information with Neutron.

Use Cases

  • An NFV MANO/VNFM system needs to ensure that a particular network I/O intensive workload is launched on a compute host with SR-IOV NIC hardware that has some specific hardware offload features (e.g. TSO and checksumming).

Proposed change

This spec proposes to implement the following changes in Nova:

  • A method to read the NIC feature information.

  • A method to store this information in the Nova DB.

  • How Nova Scheduler PCI filter will match this new information.

Also in this spec will be described how a Neutron port must be defined to include these NIC features. This information will be added to the OpenStack manuals and devref.

NIC feature information

The libvirt API currently provides the feature list of a NIC device. Using the command line utility we can retrieve the following information

$ virsh nodedev-dumpxml net_ens785_68_05_ca_34_83_60
  <capability type='net'>
    <link state='down'/>
    <feature name='rx'/>   <-- example of NIC feature
    <feature name='tx'/>
    <feature name='sg'/>
    <feature name='tso'/>
    <feature name='gso'/>
    <feature name='gro'/>
    <feature name='rxvlan'/>
    <feature name='txvlan'/>
    <feature name='rxhash'/>
    <feature name='rdma'/>
    <feature name='txudptnl'/>
    <capability type='80203'/>

The parent of a NIC device is always a unique PCI device and the only child of this PCI devide is the NIC device. This spec proposes to add a new member to nova.virt.libvirt.config.LibvirtConfigNodeDevicePciCap class, called ‘net_features’. This member will be a list of strings, e.g., ‘HW_NIC_OFFLOAD_RX’, ‘HW_NIC_OFFLOAD_TSO’ or ‘HW_NIC_OFFLOAD_RSHASH’. This list is empty by default. If a PCI device is not a NIC interface or doesn’t have any feature, the list will remain empty.

Store the NIC features information

No changes are needed in the database. The NIC information per PCI device will be stored in pci_devices.extra_info under a dictionary labeled capabilities. This dictionary will contain all discovered PCI capabilities, grouped in types. In this case, because the features are related with networking capabilities, these will be contained in a list called network

extra_info: {'capabilities':
                {'network': ['HW_NIC_OFFLOAD_RX', 'HW_NIC_OFFLOAD_SG',
                             'HW_NIC_OFFLOAD_TSO', 'HW_NIC_OFFLOAD_TX']}

As seen in the example above, the strings representing network capabilities are traits belonging to os-traits project. Those traits are located under os_traits.hw.nic directory [2]. Any other string not found in os-traits will be discarded from capabilities:network list and a warning message will be logged, but no exception will be risen.

Neutron port binding:profile

The Neutron data model and API is already defined. No modifications in Neutron project are needed.

E.g., how to define a Neutron port and request some specific NIC features, defined in the binding profile

$ openstack port create --binding-profile
    '{"capabilities": ["HW_NIC_OFFLOAD_RX", "HW_NIC_OFFLOAD_TSO"]}'
    --network private port1

Nova Scheduler filter PciPassthroughFilter

As it works now, the PCI request information during the boot of a virtual machine will come both from the PCI alias information provided in the flavor and the Neutron port definition passed in the boot command. With this feature, the Neutron port would be able to contain a list of NIC features.

To add this new parameter to the filter, PciDeviceStats PCI device pools will contain a new tag key (‘capabilities.network’). Because every virtual function in the pool belongs to the same PCI device, all of them have the same NIC features.

If the PCI request spec from a Neutron port has a capabilities_network parameter, the filter will try to match this value with the one stored in the PCI device pools.

capabilities_network parameter in both the request spec and the PCI device stats are lists. Currently the PCI passthrough filter only matches string parameters [3]. This spec proposes to change this matching function to accept both strings and lists:

  • If a string is passed, the function will pass if both strings are equal.

  • If a list is passed, the function will pass if all elements in the request spec list are contained in the PCI device pool list.


  • To create a new member in Neutron port, containing the feature information as a list of strings. However, this change doesn’t add any value because currently there is a place, binding:profile, to define and store this information.

Data model impact


REST API impact


Security impact


Notifications impact


Other end user impact


Performance Impact

The Nova Scheduler PciPassthroughFilter needs to include the ‘NIC features’ parameter into the checking loop, adding an extra time per host checked. In return, the list of passed hosts could be shorter because of the new restrictions.

Other deployer impact

libvirt implemented the SR-IOV NIC offload feature discovery on version 1.2.14 [1].

Developer impact




Primary assignees:

Rodolfo Alonso <rodolfo.alonso.hernandez@intel.com> Sean K Mooney <sean.k.mooney@intel.com>

Work Items

  1. Implement a method to read the NIC feature information.

  2. Implement a method to store this information in the Nova DB.

  3. Design how Nova Scheduler PCI filter will match this new information.

  4. Add documentation illustrating how to correctly use filter and sort params when listing servers.

  5. Add enough documentation to NFV MANO manuals and devref.

  6. When Resource Provider project is fully implemented, migrate this feature and add all NIC features to os-traits.




Few unittest needs to be adjusted to work correctly. All the unittest and functional should be passed after the change.

Once the third-party CI with specific hardware is added to Jenkins, new tests will be added.

Documentation Impact

The devref needs to describe:

  • Which new information is added to pci_devices and where is obtained.

  • How to define the new parameters in the Nova Flavor extra specs fields.

  • How to define a new Neutron port with these new parameters.

Neutron docs SR-IOV section must also contain this information.




Release Name