zun/specs/pci-device-model.rst

PCI passthrough device modeling

Related Launchpad Blueprint: https://blueprints.launchpad.net/zun/+spec/container-pci-device-modeling

PCI passthrough enables full access and direct control of a physical PCI device in a Zun container. With PCI passthrough, the full physical device is assigned to only one container and cannot be shared. This mechanism is generic for any kind of PCI devices. For example, it runs with a Network Interface Card (NIC), Graphics Processing Unit (GPU), or any other devices that can be attached to a PCI bus. To properly use the devices, containers are required to install the correct driver of the device.

Some PCI devices provide Single Root I/O Virtualization and Sharing (SR-IOV) capabilities to share the PCI device among different VMs or containers. When SR-IOV is used, a physical device is virtualized and appears as multiple PCI devices. Virtual PCI devices are assigned to the same or different containers.

Since release Ocata, Openstack Nova enables flavor-based PCI-passthough device management. This design will not depend on the Nova's implementation of PCI-passthough work. However the design and implementation in Zun will refer to the existing of Nova work and try to be consistent with Nova's implementation.

Problem description

Currently, Zun scheduler can only schedule work loads with requests of regular compute resources, such as CPUs, RAMs. There are some emerging use cases requiring containers to access resources such as GPUs, NICs and so on. PCI passthrough and SR-IOV are the common technology to enable such use cases. To support the new use cases, the new resources will be added to Zun compute resource model, and allow Zun scheduler to place the work load according to the availability of the resources.

Proposed change

1. Introduce a new configuration to abstract the PCI devices at Zun Compute. A new PCI passthrough whitelist configuration will allow cloud administrators to explicitly define a list PCI devices to be available for Zun Compute services. The whitelist of PCI devices should be common for both network PCI devices and other compute or storage PCI devices. The PCI whitelist can be implemented exactly as Nova[1]: In zun.conf, whitelist entries are defined as the following:

pci_passthrough_whitelist = {<entry>}
Each whitelist entry is defined in the format:
   ["vendor_id": "<id>",]
   ["product_id": "<id>",]
   ["address": "[[[[<domain>]:]<bus>]:][<slot>][.[<function>]]" |
    "devname": "PCI Device Name",]
   ["tag":"<tag_value>",]

The valid key values are:
  "vendor_id": Vendor ID of the device in hexadecimal.
  "product_id": Product ID of the device in hexadecimal.
  "address": PCI address of the device.
  "devname": Device name of the device (for e.g. interface name). Not all
          PCI devices have a name.
  "<tag>": Additional <tag> and <tag_value> used for matching PCI devices.
        Supported <tag>: "physical_network". The pre-defined tag
        "physical_network" is used to define the physical network, that
        the SR-IOV NIC devices are attached to.

2. Introduce a new configuration pci alias to allow zun to specify the PCI device without needing to repeat all the PCI property requirement. For example,

alias = {
    "name": "QuickAssist",
    "product_id": "0443",
    "vendor_id": "8086",
    "device_type": "type-PCI"
}

defines an alias for the Intel QuickAssist card. Valid key values are
"name": Name of the PCI alias.
"product_id": Product ID of the device in hexadecimal.
"vendor_id": Vendor ID of the device in hexadecimal.
"device_type": Type of PCI device. Valid values are: "type-PCI",
               "type-PF" and "type-VF".

The typical workflow will be as following:

1. A cloud admin configures PCI-PASSTHROUGH alias at /etc/zun.conf on the openstack controller nodes.

[default]
pci_alias = {
    "name": "QuickAssist",
    "product_id": "0443",
    "vendor_id": "8086",
    "device_type": "type-PCI"
}

2. Cloud admin enables the PCI-PASSTHROUGH filter to /etc/zun.conf at openstack controller nodes.

scheduler_available_filters=zun.scheduler.filters.all_filters
scheduler_default_filters= ..., PciPassthroughFilter

3. Cloud admin restarts the Zun-API service to make the configuration effective;
4. Cloud admin adds available PCI Passthrough devices to the whitelist of /etc/zun.conf at Zun compute nodes. An example can be the following:

[default]
pci_passthrough_whitelist = {
    "product_id": "0443",
    "vendor_id": "8086",
    "device_type": "type-PCI",
    "address": ":0a:00."
}
All PCI devices matching the vendor_id and product_id are added to the pool
of PCI devices available for passthrough to Zun containers.

5. Cloud admin restarts Zun Compute service to make the configuration effective.

6. Each Zun Compute service updates the PCI-Passthough devices' availability to Zun Scheduler perioadially.

7. Cloud user creates a new container with request of a PCI-Passthrough device. For example, the following command will create a test_QuickAssist container with two PCI devices named "QuickAssist" attached. The design and implementation details of creating a workload with PCI_Passthrough devices are out of the scope of this design spec. Please refer to the other blueprints (TBD) for more details.

   $ zun create --pci_passthrough QuickAssist:1 test_QuickAssist

Alternatives

It is a more desirable way to define workloads using flavors. PCI-Passthough configurations, in particularly pci_alias can be included in the flavor configuration [2][3]. Thus users will use the flavor to specify the PCI device to be used for container. Integration with OpenStack Cyborg is another mid to long term alternative[4]. Cyborg as a service for managing accelerators of any kind needs to cooperate with Zun on two planes: first, Cyborg should inform Zun about the resources through placement API[5], so that scheduler can leverage user request for particular functionality into assignment of specific resource using resource provider which possess an accelerator; second, Cyborg should be able to provide information how Zun compute can attach particular resource to containers.

Data model impact

• Introduce a new object list pci-alias, which is a list of alias object:

fields = {
    "name" : fields.StringField(nullable=False),
    "vendor_id": fields.StringField(nullable=False),
    "product_id": fields.StringField(nullable=False),
    "device_type": fields.StringField(nullable=False)
}

• Introduce a new field in the container object called 'pci-alias-usage',

  for example:

  "pci_alias_name": fields.StringField(nullable=False), "count": fields.IntField(nullable=True)

• Add pci-devices to the compute_node object. Each pci-device should have the following fields as an example:

{
    "vendor_id": fields.StringField(nullable=False),
    "product_id": fields.StringField(nullable=False),
    "address": fields.StringField(nullable=True),
    "devname": fields.StringField(nullable=True),
    "physical_network": fields.StringField(nullable=True),
}

REST API impact

None

Security impact

None

Notifications impact

None

Other end user impact

None

Performance Impact

None

Other deployer impact

None

Developer impact

None

Implementation

Assignee(s)

Primary assignee:

Other contributors:

Work Items

1. Implement codes to read and validate pci_alias configuration;
2. Implement codes to read and validate pci_whitelist configuration;
3. Implement new pci-alias model and the verify if a pci_alias match a given pci_whitelist entry upon a new zun compute service available;
4. Implement unit/integration test.

Dependencies

The full function of enable Pci passthrough will depend on other component in Zun or outside of Zun such as Neutron and Kuryr; Support GPU PCI-PASSTHROUGH will require the support of NVIDIA docker run-time; Support SR-IOV NIC PCI-PASSTHROUGH will require SR-IOV port binding from Kuryr.

Testing

Each patch will have unit tests, and Tempest functional tests covered.

Documentation Impact

A set of documentation for this new feature will be required.

References

[1] https://docs.openstack.org/nova/latest/admin/pci-passthrough.html

[2] PCI flavor-based device assignment https://docs.google.com/

document/d/1vadqmurlnlvZ5bv3BlUbFeXRS_wh-dsgi5plSjimWjU

[3] https://wiki.openstack.org/wiki/PCI_passthrough_SRIOV_support

[4] https://review.openstack.org/#/c/448228/

[5] https://docs.openstack.org/nova/latest/user/placement.html