CPU Policy

Scenarios

By default, kubelet uses CFS quotas to enforce pod CPU limits. When the node runs many CPU-bound pods, the workload can move to different CPU cores depending on whether the pod is throttled and which CPU cores are available at scheduling time. Many workloads are not sensitive to this migration and thus work fine without any intervention. Some applications are CPU-sensitive. They are sensitive to:

• CPU throttling
• Context switching
• Processor cache misses
• Cross-socket memory access
• Hyperthreads that are expected to run on the same physical CPU card

If your workloads are sensitive to any of these items and CPU cache affinity and scheduling latency significantly affect workload performance, kubelet allows alternative CPU management policies (CPU binding) to determine some placement preferences on the node. The CPU manager preferentially allocates resources on a socket and full physical cores to avoid interference.

Constraints

The CPU management policy cannot take effect on physical cloud server nodes.

Enabling the CPU Management Policy

A CPU management policy is specified by the kubelet flag --cpu-manager-policy. By default, Kubernetes supports the following policies:

• Disabled (none): the default policy. The none policy explicitly enables the existing default CPU affinity scheme, providing no affinity beyond what the OS scheduler does automatically.
• Enabled (static): The static policy allows containers in guaranteed pods with integer GPU requests to be granted increased CPU affinity and exclusivity on the node.

When creating a cluster, you can configure the CPU management policy in Advanced Settings.

You can also configure the policy in a node pool. The configuration will change the kubelet flag --cpu-manager-policy on the node. Log in to the CCE console, click the cluster name, access the cluster details page, and choose Nodes in the navigation pane. On the page displayed, click the Node Pools tab. Choose More > Manage in the Operation column of the target node pool, and change the value of cpu-manager-policy to static.

Allowing Pods to Exclusively Use the CPU Resources

Prerequisites:

• Enable the static policy on the node. For details, see Enabling the CPU Management Policy.
• Both requests and limits must be configured in pods and their values must be the same integer.
• If an init container needs to exclusively use CPUs, set its requests to the same as that of the service container. Otherwise, the service container does not inherit the CPU allocation result of the init container, and the CPU manager reserves more CPU resources than supposed. For more information, see App Containers can't inherit Init Containers CPUs - CPU Manager Static Policy.

You can use Scheduling Policies (Affinity/Anti-affinity) to schedule the configured pods to the nodes where the static policy is enabled. In this way, the pods can exclusively use the CPU resources.

kind: Deployment
apiVersion: apps/v1
metadata:
  name: test
spec:
  replicas: 1
  selector:
    matchLabels:
      app: test
  template:
    metadata:
      labels:
        app: test
    spec:
      containers:
        - name: container-1
          image: nginx:alpine
          resources:
            requests:
              cpu: 2           # The value must be an integer and must be the same as that in limits.
              memory: 2048Mi
            limits:
              cpu: 2           # The value must be an integer and must be the same as that in requests.
              memory: 2048Mi
      imagePullSecrets:
        - name: default-secret