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Using Topology Manager

Topology Manager collects hints from the CPU Manager, Device Manager, and other Hint Providers to align pod resources, such as CPU, SR-IOV VFs, and other device resources, for all Quality of Service (QoS) classes on the same non-uniform memory access (NUMA) node.

Topology Manager uses topology information from collected hints to decide if a pod can be accepted or rejected on a node, based on the configured Topology Manager policy and Pod resources requested.

Topology Manager is useful for workloads that use hardware accelerators to support latency-critical execution and high throughput parallel computation.

To use Topology Manager you must use the CPU Manager with the static policy. For more information on CPU Manager, see Using CPU Manager.

Topology Manager policies

Topology Manager aligns Pod resources of all Quality of Service (QoS) classes by collecting topology hints from Hint Providers, such as CPU Manager and Device Manager, and using the collected hints to align the Pod resources.

To align CPU resources with other requested resources in a Pod spec, the CPU Manager must be enabled with the static CPU Manager policy.

Topology Manager supports four allocation policies, which you assign in the cpumanager-enabled custom resource (CR):

none policy

This is the default policy and does not perform any topology alignment.

best-effort policy

For each container in a pod with the best-effort topology management policy, kubelet calls each Hint Provider to discover their resource availability. Using this information, the Topology Manager stores the preferred NUMA Node affinity for that container. If the affinity is not preferred, Topology Manager stores this and admits the pod to the node.

restricted policy

For each container in a pod with the restricted topology management policy, kubelet calls each Hint Provider to discover their resource availability. Using this information, the Topology Manager stores the preferred NUMA Node affinity for that container. If the affinity is not preferred, Topology Manager rejects this pod from the node, resulting in a pod in a Terminated state with a pod admission failure.

single-numa-node policy

For each container in a pod with the single-numa-node topology management policy, kubelet calls each Hint Provider to discover their resource availability. Using this information, the Topology Manager determines if a single NUMA Node affinity is possible. If it is, the pod is admitted to the node. If a single NUMA Node affinity is not possible, the Topology Manager rejects the pod from the node. This results in a pod in a Terminated state with a pod admission failure.

Setting up Topology Manager

To use Topology Manager, you must enable the LatencySensitive Feature Gate and configure the Topology Manager policy in the cpumanager-enabled custom resource (CR). This file might exist if you have set up CPU Manager. If the file does not exist, you can create the file.

Prequisites

  • Configure the CPU Manager policy to be static. Refer to Using CPU Manager in the Scalability and Performance section.

Procedure

To activate Topololgy Manager:

  1. Edit the FeatureGate object to add the LatencySensitive feature set:

    $ oc edit featuregate/cluster
    apiVersion: config.openshift.io/v1
kind: FeatureGate
metadata:
  annotations:
    release.openshift.io/create-only: "true"
  creationTimestamp: 2020-06-05T14:41:09Z
  generation: 2
  managedFields:
  - apiVersion: config.openshift.io/v1
    fieldsType: FieldsV1
    fieldsV1:
      f:metadata:
        f:annotations:
          .: {}
          f:release.openshift.io/create-only: {}
      f:spec: {}
    manager: cluster-version-operator
    operation: Update
    time: 2020-06-05T14:41:09Z
  - apiVersion: config.openshift.io/v1
    fieldsType: FieldsV1
    fieldsV1:
      f:spec:
        f:featureSet: {}
    manager: oc
    operation: Update
    time: 2020-06-05T15:21:44Z
  name: cluster
  resourceVersion: "28457"
  selfLink: /apis/config.openshift.io/v1/featuregates/cluster
  uid: e802e840-89ee-4137-a7e5-ca15fd2806f8
spec:
  featureSet: LatencySensitive (1)
...
    1 Add the LatencySensitive feature set in a comma-separated list.

  2. Configure the Topology Manager policy in the cpumanager-enabled custom resource (CR).

    $ oc edit KubeletConfig cpumanager-enabled
    apiVersion: machineconfiguration.openshift.io/v1
kind: KubeletConfig
metadata:
  name: cpumanager-enabled
spec:
  machineConfigPoolSelector:
    matchLabels:
      custom-kubelet: cpumanager-enabled
  kubeletConfig:
     cpuManagerPolicy: static (1)
     cpuManagerReconcilePeriod: 5s
     topologyManagerPolicy: single-numa-node (2)
    1 This parameter must be static.
    2 Specify your selected Topology Manager policy. Here, the policy is single-numa-node. Acceptable values are: default, best-effort, restricted, single-numa-node.
Additional resources

For more information on CPU Manager, see Using CPU Manager.

Pod interactions with Topology Manager policies

The example Pod specs below help illustrate pod interactions with Topology Manager.

The following pod runs in the BestEffort QoS class because no resource requests or limits are specified.

spec:
  containers:
  - name: nginx
    image: nginx

The next pod runs in the Burstable QoS class because requests are less than limits.

spec:
  containers:
  - name: nginx
    image: nginx
    resources:
      limits:
        memory: "200Mi"
      requests:
        memory: "100Mi"

If the selected policy is anything other than none, Topology Manager would not consider either of these Pod specifications.

The last example pod below runs in the Guaranteed QoS class because requests are equal to limits.

spec:
  containers:
  - name: nginx
    image: nginx
    resources:
      limits:
        memory: "200Mi"
        cpu: "2"
        example.com/device: "1"
      requests:
        memory: "200Mi"
        cpu: "2"
        example.com/device: "1"

Topology Manager would consider this pod. The Topology Manager consults the CPU Manager static policy, which returns the topology of available CPUs. Topology Manager also consults Device Manager to discover the topology of available devices for example.com/device.

Topology Manager will use this information to store the best Topology for this container. In the case of this pod, CPU Manager and Device Manager will use this stored information at the resource allocation stage.