Use Kubernetes CPU Manager Static Policy’s Guaranteed QoS class with exclusive CPUs¶

You can launch a container pinned to a particular set of CPU cores using the Kubernetes CPU manager static policy’s Guaranteed QoS class.

Prerequisites

You will need to enable the Kubernetes CPU Manager’s Static Policy for the target worker node(s).

See StarlingX Administrator Tasks: Kubernetes CPU Manager Policies for details on how to enable this CPU management mechanism.

Procedure

Create your pod with <resources:requests:cpu/memory> and <resources:limits:cpu/memory> according to https://kubernetes.io/docs/tasks/administer-cluster/cpu-management-policies/#cpu-management-policies, in order to select the Guaranteed QoS class with exclusive CPUs. Specifically this requires either:
- <resources:requests:cpu/memory> to be equal to <resources:limits:cpu/memory>, and cpu to be an integer value > 1,
or
- only <resources:limits:cpu/memory> to be specified, and cpu to be an integer value > 1.
The CPUs allocated to the pod will be exclusive (or dedicated/pinned) to the pod, and taken from the CPUs configured as ‘application’ function for the host. Processes within the pod can float across the set of CPUs allocated to the pod, unless the application in the pod explicitly pins the process(es) to a subset of the CPUs.

For example:
```
% cat <<EOF > stress-cpu-pinned.yaml
apiVersion: v1
kind: Pod
metadata:
  name: stress-ng-cpu
spec:
  containers:
  - name: stress-ng-app
    image: alexeiled/stress-ng
    imagePullPolicy: IfNotPresent
    command: ["/stress-ng"]
    args: ["--cpu", "10", "--metrics-brief", "-v"]
    resources:
      requests:
        cpu: 2
        memory: "2Gi"
      limits:
        cpu: 2
        memory: "2Gi"
  nodeSelector:
    kubernetes.io/hostname: worker-1
EOF
```
You will likely need to adjust some values shown above to reflect your deployment configuration. For example, on an AIO-SX or AIO-DX system. worker-1 would probably become controller-0 or controller-1.

The significant addition to this definition in support of CPU pinning, is the resources section , which sets a CPU resource request and limit of 2.
Apply the definition.
```
% kubectl apply -f stress-cpu-pinned.yaml
```
You can SSH to the worker node and run top, and type ‘1’ to see CPU details per core:

Describe the pod or node to see the CPU Request, CPU Limits and that it is in the “Guaranteed” QoS Class.

For example:

% kubectl describe <node>
Namespace                  Name           CPU Requests  CPU Limits  Memory Requests  Memory Limits  AGE
---------                  ----           ------------  ----------  ---------------  -------------  ---
default                    stress-ng-cpu  2 (15%)       2 (15%)     2Gi (7%)         2Gi (7%)       9m31s

% kubectl describe <pod> stress-ng-cpu
...
QoS Class: Guaranteed

Delete the container.

% kubectl delete -f stress-cpu-pinned.yaml