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Merge pull request #48356 from nokia/KEP-4540-strict-cpu-reservation-doc 

KEP-4540: CPUManager strict-cpu-reservation policy option documentation
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Kubernetes Prow Robot 2024-11-25 21:02:57 +00:00 committed by GitHub
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18
content/en/docs/tasks/administer-cluster/cpu-management-policies.md
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@ -268,6 +268,7 @@ The following policy options exist for the static `CPUManager` policy:
* `distribute-cpus-across-numa` (alpha, hidden by default) (1.23 or higher)
* `align-by-socket` (alpha, hidden by default) (1.25 or higher)
* `distribute-cpus-across-cores` (alpha, hidden by default) (1.31 or higher)
* `strict-cpu-reservation` (alpha, hidden by default) (1.32 or higher)
If the `full-pcpus-only` policy option is specified, the static policy will always allocate full physical cores.
By default, without this option, the static policy allocates CPUs using a topology-aware best-fit allocation.
@ -318,7 +319,6 @@ the benefit of reducing contention diminishes. Conversely, default behavior
can help in reducing inter-core communication overhead, potentially providing
better performance under high load conditions.
The `full-pcpus-only` option can be enabled by adding `full-pcpus-only=true` to
the CPUManager policy options.
Likewise, the `distribute-cpus-across-numa` option can be enabled by adding
@ -334,3 +334,19 @@ The `distribute-cpus-across-cores` option can be enabled by adding
`distribute-cpus-across-cores=true` to the `CPUManager` policy options.
It cannot be used with `full-pcpus-only` or `distribute-cpus-across-numa` policy
options together at this moment.
The `reservedSystemCPUs` parameter in [KubeletConfiguration](/docs/reference/config-api/kubelet-config.v1beta1/),
or the deprecated kubelet command line option `--reserved-cpus`, defines an explicit CPU set for OS system daemons
and kubernetes system daemons. More details of this parameter can be found on the
[Explicitly Reserved CPU List](/docs/tasks/administer-cluster/reserve-compute-resources/#explicitly-reserved-cpu-list) page.
By default this isolation is implemented only for guaranteed pods with integer CPU requests not for burstable and best-effort pods
(and guaranteed pods with fractional CPU requests). Admission is only comparing the cpu requests against the allocatable cpus.
Since the cpu limit is higher than the request, the default behaviour allows burstable and best-effort pods to use up the capacity
of `reservedSystemCPUs` and cause host OS services to starve in real life deployments.
If the `strict-cpu-reservation` policy option is enabled, the static policy will not allow
any workload to use the CPU cores specified in `reservedSystemCPUs`.
The `strict-cpu-reservation` option can be enabled by adding `strict-cpu-reservation=true` to
the CPUManager policy options followed by removing the `/var/lib/kubelet/cpu_manager_state` file and restart kubelet.