OCPDOCS 17899 Document Kernel PSI Enablement in OpenShift 4.21

modules/nodes-nodes-psi-enable.adoc

@@ -0,0 +1,75 @@
+// Module included in the following assemblies:
+//
+// * nodes/nodes/nodes-nodes-managing.adoc
+
+:_mod-docs-content-type: PROCEDURE
+[id="nodes-nodes-psi-enable_{context}"]
+= Enabling Pressure Stall Information (PSI) monitoring
+
+[role="_abstract"]
+You can enable Linux Pressure Stall Information monitoring by using a `MachineConfig` object. Enabling PSI monitoring makes PSI metrics (pressure stall information) for CPU, memory, and IO available for your cluster.
+
+[NOTE]
+====
+The performance impact of enabling PSI is negligible with the benefit of gaining critical resource pressure visibility for better scheduling and eviction decisions. This was tested on worker nodes (m5.2xl) on the AWS platform. For latency sensitive environments, we suggest testing it before enabling it on production. Enable it on 1 worker first, monitor for the performance impact, and gradually roll out to more workers.
+====
+
+.Prerequisites
+
+. Obtain the label associated with the static `MachineConfigPool` CR for the type of node you want to configure.
+Perform one of the following steps:
+
+.. View the machine config pool:
++
+[source,terminal]
+----
+$ oc describe machineconfigpool <name>
+----
++
+For example:
++
+[source,terminal]
+----
+$ oc describe machineconfigpool worker
+----
++
+.Example output
+[source,yaml]
+----
+apiVersion: machineconfiguration.openshift.io/v1
+kind: MachineConfigPool
+metadata:
+  creationTimestamp: 2019-02-08T14:52:39Z
+  generation: 1
+  labels:
+    custom-kubelet: set-kubelet-config <1>
+----
+<1> If a label has been added it appears under `labels`.
+
+.. If the label is not present, add a key/value pair:
++
+[source,terminal]
+----
+$ oc label machineconfigpool worker custom-kubelet=set-kubelet-config
+----
+
+.Procedure
+
+. Create a YAML file similar to the following that contains the machine configuration:
++
+[source,yaml]
+----
+apiVersion: machineconfiguration.openshift.io/v1
+kind: MachineConfig
+metadata:
+  labels:
+    machineconfiguration.openshift.io/role: <label>
+  name: 99-openshift-machineconfig-<label>-kargs
+spec:
+  kernelArguments:
+    - psi=1
+----
+where:
++
+`spec.kernelArguments.psi=1` Specifies that Pressure Stall Information (PSI) monitoring is enabled.
+

nodes/nodes/nodes-nodes-managing.adoc

@@ -34,6 +34,8 @@ include::modules/nodes-nodes-parallel-container-pulls-configure.adoc[leveloffset
 
 include::modules/nodes-control-plane-osp-migrating.adoc[leveloffset=+1]
 
+include::modules/nodes-nodes-psi-enable.adoc[leveloffset=+1]
+
 [role="_additional-resources"]
 == Additional resources