taikun.cloud

Taikun OCP Guide

Table of Contents

Attaching virtual GPU devices to guests

Important

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

The virtual GPU feature in Nova allows a deployment to provide
specific GPU types for instances using physical GPUs that can provide
virtual devices.

For example, a single Intel GVT-g
or a NVIDIA
GRID vGPU
physical Graphics Processing Unit (pGPU) can be
virtualized as multiple virtual Graphics Processing Units (vGPUs) if the
hypervisor supports the hardware driver and has the capability to create
guests using those virtual devices.

This feature is highly dependent on the version of libvirt and the
physical devices present on the host. In addition, the vendor’s vGPU
driver software must be installed and configured on the host at the same
time.

Caveats are mentioned in the Caveats
section.

To enable virtual GPUs, follow the steps below:

  1. Enable GPU types
    (Compute)
  2. Configure a flavor
    (Controller)

Enable GPU types (Compute)

  1. Specify which specific GPU type(s) the instances would get.

    Edit devices.enabled_mdev_types:

    [devices]
    enabled_mdev_types = nvidia-35

    If you want to support more than a single GPU type, you need to
    provide a separate configuration section for each device. For
    example:

    [devices]
    enabled_mdev_types = nvidia-35, nvidia-36
    
    [mdev_nvidia-35]
    device_addresses = 0000:84:00.0,0000:85:00.0
    
    [mdev_nvidia-36]
    device_addresses = 0000:86:00.0

    where you have to define which physical GPUs are supported per GPU
    type.

    If the same PCI address is provided for two different types,
    nova-compute will refuse to start and issue a specific error in the
    logs.

    To know which specific type(s) to mention, please refer to How to discover a GPU type.

    21.0.0

    Supporting multiple GPU types is only supported by the Ussuri release
    and later versions.

  2. Restart the nova-compute service.

    Warning

    Changing the type is possible but since existing physical GPUs can’t
    address multiple guests having different types, that will make Nova
    return you a NoValidHost if existing instances with the original type
    still exist. Accordingly, it’s highly recommended to instead deploy the
    new type to new compute nodes that don’t already have workloads and
    rebuild instances on the nodes that need to change types.

Configure a flavor
(Controller)

Configure a flavor to request one virtual GPU:

$ openstack flavor set vgpu_1 --property "resources:VGPU=1"

Note

As of the Queens release, all hypervisors that support virtual GPUs
only accept a single virtual GPU per instance.

The enabled vGPU types on the compute hosts are not exposed to API
users. Flavors configured for vGPU support can be tied to host
aggregates as a means to properly schedule those flavors onto the
compute hosts that support them. See /admin/aggregates for more information.

Create instances with
virtual GPU devices

The nova-scheduler selects a destination host that has
vGPU devices available by calling the Placement API for a specific VGPU
resource class provided by compute nodes.

$ openstack server create --flavor vgpu_1 --image cirros-0.3.5-x86_64-uec --wait test-vgpu

How to discover a GPU type

Virtual GPUs are seen as mediated devices. Physical PCI devices (the
graphic card here) supporting virtual GPUs propose mediated device
(mdev) types. Since mediated devices are supported by the Linux kernel
through sysfs files after installing the vendor’s virtual GPUs driver
software, you can see the required properties as follows:

$ ls /sys/class/mdev_bus/*/mdev_supported_types
/sys/class/mdev_bus/0000:84:00.0/mdev_supported_types:
nvidia-35  nvidia-36  nvidia-37  nvidia-38  nvidia-39  nvidia-40  nvidia-41  nvidia-42  nvidia-43  nvidia-44  nvidia-45

/sys/class/mdev_bus/0000:85:00.0/mdev_supported_types:
nvidia-35  nvidia-36  nvidia-37  nvidia-38  nvidia-39  nvidia-40  nvidia-41  nvidia-42  nvidia-43  nvidia-44  nvidia-45

/sys/class/mdev_bus/0000:86:00.0/mdev_supported_types:
nvidia-35  nvidia-36  nvidia-37  nvidia-38  nvidia-39  nvidia-40  nvidia-41  nvidia-42  nvidia-43  nvidia-44  nvidia-45

/sys/class/mdev_bus/0000:87:00.0/mdev_supported_types:
nvidia-35  nvidia-36  nvidia-37  nvidia-38  nvidia-39  nvidia-40  nvidia-41  nvidia-42  nvidia-43  nvidia-44  nvidia-45

Checking
allocations and inventories for virtual GPUs

Note

The information below is only valid from the 19.0.0 Stein release.
Before this release, inventories and allocations related to a
VGPU resource class are still on the root resource provider
related to the compute node. If upgrading from Rocky and using the
libvirt driver, VGPU inventory and allocations are moved to
child resource providers that represent actual physical GPUs.

The examples you will see are using the osc-placement
plugin
for OpenStackClient. For details on specific commands, see
its documentation.

  1. Get the list of resource providers
    $ openstack resource provider list
    +--------------------------------------+---------------------------------------------------------+------------+
    | uuid                                 | name                                                    | generation |
    +--------------------------------------+---------------------------------------------------------+------------+
    | 5958a366-3cad-416a-a2c9-cfbb5a472287 | virtlab606.xxxxxxxxxxxxxxxxxxxxxxxxxxx                  |          7 |
    | fc9b9287-ef5e-4408-aced-d5577560160c | virtlab606.xxxxxxxxxxxxxxxxxxxxxxxxxxx_pci_0000_86_00_0 |          2 |
    | e2f8607b-0683-4141-a8af-f5e20682e28c | virtlab606.xxxxxxxxxxxxxxxxxxxxxxxxxxx_pci_0000_85_00_0 |          3 |
    | 85dd4837-76f9-41f2-9f19-df386017d8a0 | virtlab606.xxxxxxxxxxxxxxxxxxxxxxxxxxx_pci_0000_87_00_0 |          2 |
    | 7033d860-8d8a-4963-8555-0aa902a08653 | virtlab606.xxxxxxxxxxxxxxxxxxxxxxxxxxx_pci_0000_84_00_0 |          2 |
    +--------------------------------------+---------------------------------------------------------+------------+

    In this example, we see the root resource provider
    5958a366-3cad-416a-a2c9-cfbb5a472287 with four other
    resource providers that are its children and where each of them
    corresponds to a single physical GPU.

  2. Check the inventory of each resource provider to see resource
    classes

    $ openstack resource provider inventory list 5958a366-3cad-416a-a2c9-cfbb5a472287
    +----------------+------------------+----------+----------+-----------+----------+-------+
    | resource_class | allocation_ratio | max_unit | reserved | step_size | min_unit | total |
    +----------------+------------------+----------+----------+-----------+----------+-------+
    | VCPU           |             16.0 |       48 |        0 |         1 |        1 |    48 |
    | MEMORY_MB      |              1.5 |    65442 |      512 |         1 |        1 | 65442 |
    | DISK_GB        |              1.0 |       49 |        0 |         1 |        1 |    49 |
    +----------------+------------------+----------+----------+-----------+----------+-------+
    $ openstack resource provider inventory list e2f8607b-0683-4141-a8af-f5e20682e28c
    +----------------+------------------+----------+----------+-----------+----------+-------+
    | resource_class | allocation_ratio | max_unit | reserved | step_size | min_unit | total |
    +----------------+------------------+----------+----------+-----------+----------+-------+
    | VGPU           |              1.0 |       16 |        0 |         1 |        1 |    16 |
    +----------------+------------------+----------+----------+-----------+----------+-------+

    Here you can see a VGPU inventory on the child resource
    provider while other resource class inventories are still located on the
    root resource provider.

  3. Check allocations for each server that is using virtual GPUs
    $ openstack server list
    +--------------------------------------+-------+--------+---------------------------------------------------------+--------------------------+--------+
    | ID                                   | Name  | Status | Networks                                                | Image                    | Flavor |
    +--------------------------------------+-------+--------+---------------------------------------------------------+--------------------------+--------+
    | 5294f726-33d5-472a-bef1-9e19bb41626d | vgpu2 | ACTIVE | private=10.0.0.14, fd45:cdad:c431:0:f816:3eff:fe78:a748 | cirros-0.4.0-x86_64-disk | vgpu   |
    | a6811fc2-cec8-4f1d-baea-e2c6339a9697 | vgpu1 | ACTIVE | private=10.0.0.34, fd45:cdad:c431:0:f816:3eff:fe54:cc8f | cirros-0.4.0-x86_64-disk | vgpu   |
    +--------------------------------------+-------+--------+---------------------------------------------------------+--------------------------+--------+
    
    $ openstack resource provider allocation show 5294f726-33d5-472a-bef1-9e19bb41626d
    +--------------------------------------+------------+------------------------------------------------+
    | resource_provider                    | generation | resources                                      |
    +--------------------------------------+------------+------------------------------------------------+
    | 5958a366-3cad-416a-a2c9-cfbb5a472287 |          8 | {u'VCPU': 1, u'MEMORY_MB': 512, u'DISK_GB': 1} |
    | 7033d860-8d8a-4963-8555-0aa902a08653 |          3 | {u'VGPU': 1}                                   |
    +--------------------------------------+------------+------------------------------------------------+
    
    $ openstack resource provider allocation show a6811fc2-cec8-4f1d-baea-e2c6339a9697
    +--------------------------------------+------------+------------------------------------------------+
    | resource_provider                    | generation | resources                                      |
    +--------------------------------------+------------+------------------------------------------------+
    | e2f8607b-0683-4141-a8af-f5e20682e28c |          3 | {u'VGPU': 1}                                   |
    | 5958a366-3cad-416a-a2c9-cfbb5a472287 |          8 | {u'VCPU': 1, u'MEMORY_MB': 512, u'DISK_GB': 1} |
    +--------------------------------------+------------+------------------------------------------------+

    In this example, two servers were created using a flavor asking for 1
    VGPU, so when looking at the allocations for each consumer
    UUID (which is the server UUID), you can see that VGPU allocation is
    against the child resource provider while other allocations are for the
    root resource provider. Here, that means that the virtual GPU used by
    a6811fc2-cec8-4f1d-baea-e2c6339a9697 is actually provided
    by the physical GPU having the PCI ID
    0000:85:00.0.

(Optional)
Provide custom traits for multiple GPU types

Since operators want to support different GPU types per compute, it
would be nice to have flavors asking for a specific GPU type. This is
now possible using custom traits by decorating child Resource Providers
that correspond to physical GPUs.

Note

Possible improvements in a future release could consist of providing
automatic tagging of Resource Providers with standard traits
corresponding to versioned mapping of public GPU types. For the moment,
this has to be done manually.

  1. Get the list of resource providers

    See Checking
    allocations and inventories for virtual GPUs
    first for getting the
    list of Resource Providers that support a VGPU resource
    class.

  2. Define custom traits that will correspond for each to a GPU
    type

    $ openstack --os-placement-api-version 1.6 trait create CUSTOM_NVIDIA_11

    In this example, we ask to create a custom trait named
    CUSTOM_NVIDIA_11.

  3. Add the corresponding trait to the Resource Provider matching the
    GPU

    $ openstack --os-placement-api-version 1.6 resource provider trait set \
        --trait CUSTOM_NVIDIA_11 e2f8607b-0683-4141-a8af-f5e20682e28c

    In this case, the trait CUSTOM_NVIDIA_11 will be added
    to the Resource Provider with the UUID
    e2f8607b-0683-4141-a8af-f5e20682e28c that corresponds to
    the PCI address 0000:85:00:0 as shown above.

  4. Amend the flavor to add a requested trait
    $ openstack flavor set --property trait:CUSTOM_NVIDIA_11=required vgpu_1

    In this example, we add the CUSTOM_NVIDIA_11 trait as a
    required information for the vgpu_1 flavor we created
    earlier.

    This will allow the Placement service to only return the Resource
    Providers matching this trait so only the GPUs that were decorated with
    will be checked for this flavor.

Caveats

Note

This information is correct as of the 17.0.0 Queens release. Where
improvements have been made or issues fixed, they are noted per
item.

  • Suspending a guest that has vGPUs doesn’t yet work because of a
    libvirt limitation (it can’t hot-unplug mediated devices from a guest).
    Workarounds using other instance actions (like snapshotting the instance
    or shelving it) are recommended until libvirt gains mdev hot-unplug
    support. If a user attempts to suspend the instance, the libvirt driver
    will raise an exception that will cause the instance to be set back to
    ACTIVE. The suspend action in the
    os-instance-actions API will have an Error
    state.

    25.0.0

    This has been resolved in the Yoga release. See bug 1948705.

  • Resizing an instance with a new flavor that has vGPU resources
    doesn’t allocate those vGPUs to the instance (the instance is created
    without vGPU resources). The proposed workaround is to rebuild the
    instance after resizing it. The rebuild operation allocates vGPUS to the
    instance.

    21.0.0

    This has been resolved in the Ussuri release. See bug 1778563.

  • Cold migrating an instance to another host will have the same
    problem as resize. If you want to migrate an instance, make sure to
    rebuild it after the migration.

    21.0.0

    This has been resolved in the Ussuri release. See bug 1778563.

  • Rescue images do not use vGPUs. An instance being rescued does
    not keep its vGPUs during rescue. During that time, another instance can
    receive those vGPUs. This is a known issue. The recommended workaround
    is to rebuild an instance immediately after rescue. However, rebuilding
    the rescued instance only helps if there are other free vGPUs on the
    host.

    18.0.0

    This has been resolved in the Rocky release. See bug 1762688.

For nested vGPUs:

Note

This information is correct as of the 21.0.0 Ussuri release. Where
improvements have been made or issues fixed, they are noted per
item.

  • If creating servers with a flavor asking for vGPUs and the user
    wants multi-create (i.e. say –max 2) then the scheduler could be
    returning a NoValidHosts exception even if each physical GPU can support
    at least one specific instance, if the total wanted capacity is not
    supported by only one physical GPU. (See bug
    1874664
    .)

    For example, creating servers with a flavor asking for vGPUs, if two
    children RPs have 4 vGPU inventories each:

    • You can ask for a flavor with 2 vGPU with –max 2.
    • But you can’t ask for a flavor with 4 vGPU and –max 2.