Merge pull request #22429 from Huang-Wei/postfilter-doc

Document the changes of scheduler PostFilter extension point

content/en/docs/concepts/configuration/pod-priority-preemption.md

@@ -51,40 +51,6 @@ Kubernetes already ships with two PriorityClasses:
 These are common classes and are used to [ensure that critical components are always scheduled first](/docs/tasks/administer-cluster/guaranteed-scheduling-critical-addon-pods/).
 {{< /note >}}
 
-## How to disable preemption
-
-{{< caution >}}
-Critical pods rely on scheduler preemption to be scheduled when a cluster
-is under resource pressure. For this reason, it is not recommended to
-disable preemption.
-{{< /caution >}}
-
-{{< note >}}
-In Kubernetes 1.15 and later, if the feature `NonPreemptingPriority` is enabled,
-PriorityClasses have the option to set `preemptionPolicy: Never`.
-This will prevent pods of that PriorityClass from preempting other pods.
-{{< /note >}}
-
-Preemption is controlled by a kube-scheduler flag `disablePreemption`, which is
-set to `false` by default.
-If you want to disable preemption despite the above note, you can set
-`disablePreemption` to `true`.
-
-This option is available in component configs only and is not available in
-old-style command line options. Below is a sample component config to disable
-preemption:
-
-```yaml
-apiVersion: kubescheduler.config.k8s.io/v1alpha1
-kind: KubeSchedulerConfiguration
-algorithmSource:
-  provider: DefaultProvider
-
-...
-
-disablePreemption: true
-```
-
 ## PriorityClass
 
 A PriorityClass is a non-namespaced object that defines a mapping from a

content/en/docs/concepts/scheduling-eviction/scheduling-framework.md

@@ -75,6 +75,14 @@ node, the scheduler will call filter plugins in their configured order. If any
 filter plugin marks the node as infeasible, the remaining plugins will not be
 called for that node. Nodes may be evaluated concurrently.
 
+### PostFilter {#post-filter}
+
+These plugins are called after Filter phase, but only when no feasible nodes
+were found for the node. Plugins are called in their configured order. If
+any postFilter plugin marks the node as `Schedulable`, the remaining plugins
+will not be called. A typical PostFilter implementation is preemption, which
+tries to make the pod schedulable by preempting other Pods.
+
 ### PreScore {#pre-score}
 
 These plugins are used to perform "pre-scoring" work, which generates a sharable

content/en/docs/reference/scheduling/config.md

@@ -158,6 +158,8 @@ extension points:
   Extension points: `QueueSort`.
 - `DefaultBinder`: Provides the default binding mechanism.
   Extension points: `Bind`.
+- `DefaultPreemption`: Provides the default preemption mechanism.
+  Extension points: `PostFilter`.
   
 You can also enable the following plugins, through the component config APIs,
 that are not enabled by default:
@@ -199,7 +201,7 @@ profiles:
   - schedulerName: default-scheduler
   - schedulerName: no-scoring-scheduler
     plugins:
-      prescore:
+      preScore:
         disabled:
         - name: '*'
       score:
@@ -230,22 +232,6 @@ the same configuration parameters (if applicable). This is because the scheduler
 only has one pending pods queue.
 {{< /note >}}
 
-## Upgrading from `v1alpha2` to `v1beta1` {#beta-changes}
-
-When migrating from `kubescheduler.config.k8s.io/v1alpha2` to `kubescheduler.config.k8s.io/v1beta1`,
-beware of the following changes, if applicable:
-
-- `.bindTimeoutSeconds` was moved as part of plugin args for `VolumeBinding`,
-  which can be configured separately per [profile](#profiles).
-- `.extenders` are updated to satisfy API standards. In particular:
-  - `.extenders` decoding is case sensitive. All fields are affected.
-  - `.extenders[*].httpTimeout` is of type `metav1.Duration`.
-  - `.extenders[*].enableHttps` is renamed to `.extenders[*].enableHTTPS`.
-- `RequestedToCapacityRatio` args decoding is case sensitive. All fields are affected.
-- `DefaultPodTopologySpread` [plugin](#scheduling-plugins) is renamed to `SelectorSpread`.
-- `Unreserve` extension point is removed from Profile definition. All `Reserve`
-  plugins implement an `Unreserve` call.
-
 ## {{% heading "whatsnext" %}}
 
 * Read the [kube-scheduler reference](https://kubernetes.io/docs/reference/command-line-tools-reference/kube-scheduler/)