documentaion: document the reactive updates feature

Signed-off-by: Talor Itzhak <titzhak@redhat.com>

docs/deployment/helm.md

@@ -153,7 +153,7 @@ We have introduced the following Chart parameters.
 ### Topology updater parameters
 
 | Name                                          | Type   | Default                 | description                                                                                                                                                                                           |
-|-----------------------------------------------|--------|---------|-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
+|-----------------------------------------------|--------|-------------------------|-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
 | `topologyUpdater.*`                           | dict   |                         | NFD Topology Updater configuration                                                                                                                                                                    |
 | `topologyUpdater.enable`                      | bool   | false                   | Specifies whether the NFD Topology Updater should be created                                                                                                                                          |
 | `topologyUpdater.createCRDs`                  | bool   | false                   | Specifies whether the NFD Topology Updater CRDs should be created                                                                                                                                     |
@@ -174,6 +174,7 @@ We have introduced the following Chart parameters.
 | `topologyUpdater.affinity`                    | dict   | {}                      | Topology updater pod [affinity](https://kubernetes.io/docs/tasks/configure-pod-container/assign-pods-nodes-using-node-affinity/)                                                                      |
 | `topologyUpdater.config`                      | dict   |                         | [configuration](../reference/topology-updater-configuration-reference)                                                                                                                                |
 | `topologyUpdater.podSetFingerprint`           | bool   | false                   | Enables compute and report of pod fingerprint in NRT objects.                                                                                                                                         |
+| `topologyUpdater.kubeletStateDir`             | string | "/host-var/lib/kubelet" | Specifies kubelet state directory path for watching state and checkpoint files. Empty value disables kubelet state tracking.                                                                          |
 
 ### Topology garbage collector parameters
 

docs/reference/topology-updater-commandline-reference.md

@@ -149,7 +149,7 @@ nfd-topology-updater -podresources-socket=/var/lib/kubelet/pod-resources/kubelet
 
 ### -pods-fingerprint
 
-Enbles the compute and report the pod set fingerprint in the NRT.
+Enables compute and report the pod set fingerprint in the NRT.
 A pod fingerprint is a compact representation of the "node state" regarding resources.
 
 Default: `false`
@@ -159,3 +159,17 @@ Example:
 ```bash
 nfd-topology-updater -pods-fingerprint
 ```
+
+### -kubelet-state-dir
+
+The `-kubelet-state-dir` specifies the path to the Kubelet state directory,
+where state and checkpoint files are stored.
+The files are mount as read-only and cannot be change by the updater.
+
+Default:  /host-var/lib/kubelet
+
+Example:
+
+```bash
+nfd-topology-updater -kubelet-state-dir=/var/lib/kubelet
+```

docs/usage/nfd-topology-updater.md

@@ -9,19 +9,28 @@ sort: 5
 
 ---
 
-NFD-Topology-Updater is preferably run as a Kubernetes DaemonSet. This assures
+NFD-Topology-Updater is preferably run as a Kubernetes DaemonSet.
-re-examination on regular intervals, capturing changes in the allocated
+This assures re-examination on regular intervals
-resources and hence the allocatable resources on a per zone basis by updating
+and/or per pod life-cycle events, capturing changes in the allocated
+resources and hence the allocatable resources on a per-zone basis by updating
 [NodeResourceTopology](custom-resources.md#noderesourcetopology) custom resources.
 It makes sure that new NodeResourceTopology instances are created for each new
 nodes that get added to the cluster.
 
 When run as a daemonset, nodes are re-examined for the allocated resources
-(to determine the information of the allocatable resources on a per zone basis
+(to determine the information of the allocatable resources on a per-zone basis
 where a zone can be a NUMA node) at an interval specified using the
 [`-sleep-interval`](../reference/topology-updater-commandline-reference.html.md#-sleep-interval)
-option. The default sleep interval is set to 60s which is the value when no
+option. The default sleep interval is set to 60s
--sleep-interval is specified.
+which is the value when no -sleep-interval is specified.
+The re-examination can be disabled by setting the sleep-interval to 0.
+
+Another option is to configure the updater to update
+the allocated resources per pod life-cycle events.
+The updater will monitor the checkpoint file stated in
+[`-kubelet-state-dir`](../reference/topology-updater-commandline-reference.md#-kubelet-state-dir)
+and triggers an update for every change occurs in the files.
+
 In addition, it can avoid examining specific allocated resources
 given a configuration of resources to exclude via [`-excludeList`](../reference/topology-updater-configuration-reference.md#excludelist)