libvirt supports composing cyborg owned vGPU into domain XML

This blueprint proposes to enable vGPU accelerator in nova and cyborg interaction.

Problem description

In order to allow operators to use cyborg to manage the lifecycle of vGPU, cyborg needs to discover the vGPUs, reports them to placement, and instruct nova to allocate a specific vgpu mdev to the instance. Cyborg managed vGPUs will not replace nova’s native vGPU capabilities [1] and will provide an alternative management mechanism in parallel to the existing nova feature.

In the current cyborg-nova interaction [2], there is still a small gap in allocating a cyborg owned vGPU to an instance. This spec proposes to support composing cyborg owned vGPU into domain XML in nova libvirt driver.

For more information about cyborg side lifecycle management (discover, data modeling etc.) of vGPU please refer to [3].

Use Cases

As an operator, I want to use Cyborg to manage the lifecycle of vGPUs.

Proposed change

  1. Define the data model in arq to track a cyborg owned vGPU.

    This data model should provide attach_handle_type to distinguish from a PCI device accelerator, and attach_handle_uuid as the mdev UUID which is used to create a mdev device in the /sys/class/mdev_bus/…, as well as the asked vgpu type of this device. The format will be like:

        'attach_handle_type': 'MDEV',
        'attach_handle_uuid': '91ac1606-427e-44bb-8233-f4ff4bf3d241',
  2. Nova virt driver merge the mdev info from arq into the XML of an instance.

    This will need to get mdevs form arq list and pass it to generate guest xml in nova/virt/libvirt/ [4]. Please be aware that the following is just the pseudocode to show the whole function and process.

    # Get mdevs accelerators from ARQ list.
    mdev_arq_list = [arq for arq in acc_info if arq['attach_handle_type'] == 'MDEV']
    xml = self._get_guest_xml(context, instance, network_info,
                              block_disk_info, image_meta,
    mdev_arq_list = [arq for arq in acc_info if arq['attach_handle_type'] == 'MDEV']
    self._guest_add_accel_mdev_devices(guest, mdev_arq_list)
    def _guest_add_accel_mdev_devices(self, guest, acc_info):
        """Adding mdev accelerators from ARQ list.
        for arq in acc_info:
            self._guest_add_mdevs(guest, arq['attach_handle_uuid'])
  3. Cyborg creates mdev device in the sys path

    In theory, if nova and cyborg both can support vGPU management, nova or cyborg should support create mdev in its own respective. Therefore, in the cyborg lifecycle management of vGPU, cyborg should creates mdev beforehead, nova virt driver uses it as an existed resousrce.

    • spawn instance interaction(arq interaction part):

      • nova-conductor requests cyborg to create and bind arq:

        • cyborg-api the cyborg-agent to create a new mdev

        • cyborg-agent sucessfully created mdev and returns result

        • cyborg start bind arq

        • cyborg arq successfully bound and notify nova that ARQ bindings are resolved for a given instance

      • nova-compute receives bound notification and GET resolved arq

      • nova-compute calls virt driver to spawn an instance

    • reboot instance interaction: when nova-compute calls cyborg GET arq API, cyborg does the db lookup and returns the expected arq.

    • host reboot: cyborg-owned vGPU will be missing from the sys path after host reboot. The cyborg agent should create the mdevs for all bound arqs on start up. Ideally it would set the binding state to “provisioning” on start up also. And we would have anohter state “unknown” that cyborg-api would report if the cyborg agent misses its heart beat. So on start up, when nova compute tries to get accel_info and reboot all the instances, it would see 1 of 3 states, “bound” if the cyborg agent started first and already completed bininding, “unknown” if the cyborg agent has not heartbeat to the cyborg conductor yet, and “provisioning” if the agent is in the process of creating the mdev. Cyborg will send the same binding complete event notification when it change the status form “provisioning” to “bound” as it does during normal arq binding.

  4. Avoid conflicts when cyborg vGPU management co-exists with nova vGPU management.

    • Use owner (nova, cyborg) trait in Placement when inventory is reported.

      • This will need to add a new namespace in os-traits: OWNER_*. Then nova/cyborg report owner trait OWNER_NOVA/OWNER_CYBORG as one of the trait when inventory is reported.

        • In the cyborg driver, it will report two traits for vGPU accelerator using the format below. For more details, pls refer to the driver spec [3].

          trait1: OWNER_CYBORG.
          trait2: CUSTOM_<VENDOR_NAME>_<PRODUCT_ID>_<Virtual_GPU_Type>.
        • In the nova side, it will need to report a new trait OWNER_NOVA for vGPU resources during inventory report.

      • When the end user makes a vGPU request, for a nova owned vGPU request, one can specify resources##:VGPU=1 in flavor. For a cyborg owned vGPU, one need specify in pre-defined device profile, then add it to flavor.

    • In libvirt driver, use a mdev_tag to identify which vGPU is the current operation request(eg. spawn, reboot) going to land. If it is cyborg vGPU, tag will be ‘ACCELERATOR’, otherwise it is ‘COMPUTE’.

      • This will need to add a new fuction _get_mdev_tag to identify this according to the given accel_info, and return a tag mdev_tag:’COMPUTE’ or ‘ACCELERATOR’ to indicate this.

      def _get_mdev_tag(self, accel_info):
          """Identify which vGPU is the current request going to land.
             parameter: accel_info
             return: mdev_tag('COMPUTE' or 'ACCELERATOR')
          if not accel_info:
              tag = 'COMPUTE'
              # here is just to show the logic specification
              if any arq in accel_info contains
                  {arq['attach_handle_type'] == 'MDEV',
                   and arq['attach_handle_info']['asked_type']}:
                      tag = 'ACCELERATOR'
                  tag = 'COMPUTE'
          return tag
      • And accordingly, we will also need new change in mdev_tag’s consumer side, the nova operations side, such as hard_reboot and spawn.



Data model impact


REST API impact


Security impact


Notifications impact


Other end user impact


Performance Impact


Other deployer impact

Deployer should make sure the device in one pci address is not configured in both Nova and Cyborg. If it is configured in both Cyborg and Nova should be able to raise this as an conflict exception. If the deployer configure same device in both Cyborg and Nova, they may report same data to Placement at the same time, we can raise conflict exception at Placement side, and return to Cyborg or Nova, and warn the deployer about the conflict device.

Developer impact


Upgrade impact

For those who want to upgrade from nova-owned vGPU to cyborg-owned vGPU, one can resize directly from a flavor with a nova managed gpu (resouces:vgpu=1 in the flavor) to a flavor with a cyborg managed vgpu (accel:device-profile=cyborg-vgpu-device-profile-name).



Primary assignee:

Wenping Song <>

Other contributors:


Feature Liaison

Feature liaison:

Brin Zhang <>

Work Items

  • Schedule vGPU resources by device profile

  • Create vGPU mdev when spawn guest

  • Unit test and function test to be added




  • New unit test should be added

Documentation Impact

  • Document need to be changed to describe this feature




Release Name