Fine-tuning and Changing the CPU Manager Policy

The behavior of the static policy can be fine-tuned using the `--cpu-manager-policy-options` flag. The flag takes a comma-separated list of `key=value` policy options. If you disable the `CPUManagerPolicyOptions` [feature gate](/docs/reference/command-line-tools-reference/feature-gates/) then you cannot fine-tune CPU manager policies. In that case, the CPU manager operates only using its default settings. In addition to the top-level `CPUManagerPolicyOptions` feature gate, the policy options are split into two groups: alpha quality (hidden by default) and beta quality (visible by default). The groups are guarded respectively by the `CPUManagerPolicyAlphaOptions` and `CPUManagerPolicyBetaOptions` feature gates. Diverging from the Kubernetes standard, these feature gates guard groups of options, because it would have been too cumbersome to add a feature gate for each individual option. ## Changing the CPU Manager Policy Since the CPU manager policy can only be applied when kubelet spawns new pods, simply changing from "none" to "static" won't apply to existing pods. So in order to properly change the CPU manager policy on a node, perform the following steps: 1. [Drain](/docs/tasks/administer-cluster/safely-drain-node) the node. 2. Stop kubelet. 3. Remove the old CPU manager state file. The path to this file is `/var/lib/kubelet/cpu_manager_state` by default. This clears the state maintained by the CPUManager so that the cpu-sets set up by the new policy won’t conflict with it. 4. Edit the kubelet configuration to change the CPU manager policy to the desired value. 5. Start kubelet. Repeat this process for every node that needs its CPU manager policy changed. Skipping this process will result in kubelet crashlooping with the following error: ``` could not restore state from checkpoint: configured policy "static" differs from state checkpoint policy "none", please drain this node and delete the CPU manager checkpoint file "/var/lib/kubelet/cpu_manager_state" before restarting Kubelet ``` {{< note >}} if the set of online CPUs changes on the node, the node must be drained and CPU manager manually reset by deleting the state file `cpu_manager_state` in the kubelet root directory. {{< /note >}} ### `none` policy configuration This policy has no extra configuration items. ### `static` policy configuration This policy manages a shared pool of CPUs that initially contains all CPUs in the node. The amount of exclusively allocatable CPUs is equal to the total number of CPUs in the node minus any CPU reservations by the kubelet `--kube-reserved` or `--system-reserved` options. From 1.17, the CPU reservation list can be specified explicitly by kubelet `--reserved-cpus` option. The explicit CPU list specified by `--reserved-cpus` takes precedence over the CPU reservation specified by `--kube-reserved` and `--system-reserved`. CPUs reserved by these options are taken, in integer quantity, from the initial shared pool in ascending order by physical core ID. This shared pool is the set of CPUs on which any containers in

This section explains how to fine-tune the `static` CPU management policy using the `--cpu-manager-policy-options` flag and feature gates. It also details the steps required to change the CPU manager policy on a node, including draining the node, stopping the kubelet, removing the old CPU manager state file, editing the kubelet configuration, and restarting the kubelet. It also describes the `none` and `static` policy configurations.