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90 lines
3.4 KiB
Plaintext
90 lines
3.4 KiB
Plaintext
// Module included in the following assemblies:
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//
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// * nodes/nodes/nodes-nodes-managing.adoc
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// * machine_configuration/machine-configs-configure.adoc
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:_mod-docs-content-type: PROCEDURE
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[id="nodes-nodes-rtkernel-arguments_{context}"]
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= Adding a real-time kernel to nodes
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Some {product-title} workloads require a high degree of determinism.While Linux is not a real-time operating system, the Linux real-time
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kernel includes a preemptive scheduler that provides the operating system with real-time characteristics.
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If your {product-title} workloads require these real-time characteristics, you can switch your machines to the Linux real-time kernel. For {product-title}, {product-version} you can make this switch using a `MachineConfig` object. Although making the change is as simple as changing a machine config `kernelType` setting to `realtime`, there are a few other considerations before making the change:
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* Currently, real-time kernel is supported only on worker nodes, and only for radio access network (RAN) use.
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* The following procedure is fully supported with bare metal installations that use systems that are certified for Red Hat Enterprise Linux for Real Time 8.
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* Real-time support in {product-title} is limited to specific subscriptions.
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* The following procedure is also supported for use with {gcp-full}.
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.Prerequisites
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* Have a running {product-title} cluster (version 4.4 or later).
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* Log in to the cluster as a user with administrative privileges.
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.Procedure
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. Create a machine config for the real-time kernel: Create a YAML file (for example, `99-worker-realtime.yaml`) that contains a `MachineConfig`
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object for the `realtime` kernel type. This example tells the cluster to use a real-time kernel for all worker nodes:
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+
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[source,terminal]
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----
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$ cat << EOF > 99-worker-realtime.yaml
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apiVersion: machineconfiguration.openshift.io/v1
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kind: MachineConfig
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metadata:
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labels:
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machineconfiguration.openshift.io/role: "worker"
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name: 99-worker-realtime
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spec:
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kernelType: realtime
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EOF
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----
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. Add the machine config to the cluster. Type the following to add the machine config to the cluster:
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+
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[source,terminal]
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----
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$ oc create -f 99-worker-realtime.yaml
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----
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. Check the real-time kernel: Once each impacted node reboots, log in to the cluster and run the following commands to make sure that the real-time kernel has replaced the regular kernel for the set of nodes you configured:
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+
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[source,terminal]
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----
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$ oc get nodes
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----
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.Example output
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[source,terminal]
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----
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NAME STATUS ROLES AGE VERSION
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ip-10-0-143-147.us-east-2.compute.internal Ready worker 103m v1.34.2
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ip-10-0-146-92.us-east-2.compute.internal Ready worker 101m v1.34.2
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ip-10-0-169-2.us-east-2.compute.internal Ready worker 102m v1.34.2
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----
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[source,terminal]
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----
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$ oc debug node/ip-10-0-143-147.us-east-2.compute.internal
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----
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.Example output
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[source,terminal]
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----
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Starting pod/ip-10-0-143-147us-east-2computeinternal-debug ...
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To use host binaries, run `chroot /host`
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sh-4.4# uname -a
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Linux <worker_node> 4.18.0-147.3.1.rt24.96.el8_1.x86_64 #1 SMP PREEMPT RT
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Wed Nov 27 18:29:55 UTC 2019 x86_64 x86_64 x86_64 GNU/Linux
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----
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The kernel name contains `rt` and text “PREEMPT RT” indicates that this is a real-time kernel.
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. To go back to the regular kernel, delete the `MachineConfig` object:
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[source,terminal]
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----
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$ oc delete -f 99-worker-realtime.yaml
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----
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