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openshift-merge-robot merged 1 commit into from
Jan 27, 2020
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docs: Add docs for kernelType #1409

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24 changes: 24 additions & 0 deletions docs/MachineConfiguration.md
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Original file line number Diff line number Diff line change
Expand Up @@ -52,6 +52,7 @@ type MachineConfigSpec struct {
Config ign.Config `json:"config"`
KernelArguments []string `json:"kernelArguments"`
Fips bool `json:"fips"`
KernelType string `json:"kernelType"`
}
```

Expand Down Expand Up @@ -115,6 +116,29 @@ Note that for 4.2 clusters this is only supported as a "day 2" operation.
#### nosmt
When a machine boots with `nosmt` Kernel Argument, it disables multi-threading on that host and the system will only utilize physical CPU cores. While applying `nosmt` on any node in the cluster, ensure that enough CPU resources are available to schedule all pods, otherwise it can lead to a degraded cluster. For example: a basic 3 master and 3 worker node cluster having 2 physical CPU cores on each node should be fine.

### KernelType

This feature is available with OCP 4.4 and onward releases as both `day 1` and `day 2` operation. It allows to choose between traditional and Real Time (RT) kernel on an RHCOS node. Supported values are
`""` or `default` for traditional kernel and `realtime` for RT kernel.

To set kernelType field during cluster install, see the [installer guide](https://github.com/openshift/installer/blob/master/docs/user/customization.md#Switching-RHCOS-host-kernel-using-KernelType).

For day 2, create a MachineConfig and apply to the cluster using `oc create -f`

Example MachineConfig to switch to RT kernel on worker nodes:
```
apiVersion: machineconfiguration.openshift.io/v1
kind: MachineConfig
metadata:
labels:
machineconfiguration.openshift.io/role: "worker"
name: worker-kerneltype
spec:
kernelType: realtime
```

**Note:** The RT kernel lowers throughput (performance) in return for improved worst-case latency bounds. This feature is intended only for use cases that require consistent low latency. For more information, see the [Linux Foundation wiki](https://wiki.linuxfoundation.org/realtime/start) and the [RHEL RT portal](https://access.redhat.com/documentation/en-us/red_hat_enterprise_linux_for_real_time/8/).

### FIPS

This allows to enable/disable [FIPS mode](https://access.redhat.com/documentation/en-us/red_hat_enterprise_linux/7/html/security_guide/chap-federal_standards_and_regulations). If any of the configuration has FIPS enabled, it'll be set. A similar restriction applies to this as for `KernelArguments` above.
Expand Down