KEP-2625: Update CPU Manager Policy Options 1.23 Beta

swatisehgal · swatisehgal · commit 45cb658af31e · 2021-09-07T17:19:12.000+01:00
- This PR updates the KEP to capture the policy name `full-pcpus-only`
  based on the implementation merged in 1.22 release.
- Explains how this feature is being used for for introduction of another policy option
- Changes pertaining to promotion to Beta
- Checks relevant fields in the Release Signoff Checklist

Signed-off-by: Swati Sehgal &lt;swsehgal@redhat.com&gt;
diff --git a/keps/prod-readiness/sig-node/2625.yaml b/keps/prod-readiness/sig-node/2625.yaml
@@ -1,3 +1,5 @@
 kep-number: 2625
 alpha:
   approver: "@johnbelamaric"
+beta:
+  approver: "@johnbelamaric"
diff --git a/keps/sig-node/2625-cpumanager-policies-thread-placement/README.md b/keps/sig-node/2625-cpumanager-policies-thread-placement/README.md
@@ -14,7 +14,7 @@
   - [Risks and Mitigations](#risks-and-mitigations)
 - [Design Details](#design-details)
   - [Proposed Change](#proposed-change)
-  - [Implementation strategy of reject-non-smt-aligned CPU Manager policy option](#implementation-strategy-of-reject-non-smt-aligned-cpu-manager-policy-option)
+  - [Implementation strategy of full-pcpus-only CPU Manager policy option](#implementation-strategy-of-full-pcpus-only-cpu-manager-policy-option)
   - [Resource Accounting](#resource-accounting)
   - [Alternatives](#alternatives)
     - [Add extra resources](#add-extra-resources)
@@ -43,16 +43,16 @@
 
 Items marked with (R) are required *prior to targeting to a milestone / release*.
 
-- [ ] (R) Enhancement issue in release milestone, which links to KEP dir in [kubernetes/enhancements](https://github.com/kubernetes/enhancements/issues/2404)
-- [ ] (R) KEP approvers have approved the KEP status as `implementable`
-- [ ] (R) Design details are appropriately documented
-- [ ] (R) Test plan is in place, giving consideration to SIG Architecture and SIG Testing input
-- [ ] (R) Graduation criteria is in place
-- [ ] (R) Production readiness review completed
+- [X] (R) Enhancement issue in release milestone, which links to KEP dir in [kubernetes/enhancements](https://github.com/kubernetes/enhancements/issues/2404)
+- [X] (R) KEP approvers have approved the KEP status as `implementable`
+- [X] (R) Design details are appropriately documented
+- [X] (R) Test plan is in place, giving consideration to SIG Architecture and SIG Testing input
+- [X] (R) Graduation criteria is in place
+- [X] (R) Production readiness review completed
 - [ ] Production readiness review approved
-- [ ] "Implementation History" section is up-to-date for milestone
+- [X] "Implementation History" section is up-to-date for milestone
 - ~~ [ ] User-facing documentation has been created in [kubernetes/website], for publication to [kubernetes.io] ~~
-- [ ] Supporting documentation e.g., additional design documents, links to mailing list discussions/SIG meetings, relevant PRs/issues, release notes
+- [X] Supporting documentation e.g., additional design documents, links to mailing list discussions/SIG meetings, relevant PRs/issues, release notes
 
 [kubernetes.io]: https://kubernetes.io/
 [kubernetes/enhancements]: https://git.k8s.io/enhancements
@@ -114,30 +114,30 @@ The impact in the shared codebase will be addressed enhancing the current testsu
 
 We propose to
 - add a new flag in Kubelet called `CPUManagerPolicyOptions` in the kubelet config or command line argument called `cpumanager-policy-options` which allows the user to specify the CPU Manager policy option.
-- add a new cpu manager option called `reject-non-smt-aligned`; if present, this option will enable further refinements of the existing static policy.
+- add a new cpu manager option called `full-pcpus-only`; if present, this option will enable further refinements of the existing static policy.
 
 The static policy allocates CPUs using a topology-aware best-fit allocation. This enhancement wants to provide stronger guarantees by restricting the allocation of threads.
 The aim is to achieve the isolation for workloads managed by Kubernetes. The other part of isolation is (as of now) not managed by Kubernetes, as described in [Explicitly Reserved CPU List](https://kubernetes.io/docs/tasks/administer-cluster/reserve-compute-resources/#explicitly-reserved-cpu-list) and [Static policy](https://kubernetes.io/docs/tasks/administer-cluster/cpu-management-policies/#static-policy).
 
-Let's summarize the key properties of the `reject-non-smt-aligned` option:
+Let's summarize the key properties of the `full-pcpus-only` option:
 - Preserve all the properties of the `static` policy.
 - Never allocate less than a physical-cpu worth amount of cores.
 - With this requirement enforced, the CPUManager allocation algorithm will guarantee avoidance of physical core sharing.
 - Should the node not have enough free physical cores, the Pod will be put in Failed state, with `SMTAlignmentError` as reason.
 
-### Implementation strategy of reject-non-smt-aligned CPU Manager policy option
+### Implementation strategy of full-pcpus-only CPU Manager policy option
 
-- In order to introduce the SMT-alignment check in CPU Manager, we introduce a new flag in Kubelet to allow the user to specify `cpumanager-policy-options` which when specified with `reject-non-smt-aligned` as its value provides the capability to modify the behaviour of static policy to strictly guarantee allocation of whole cores to a workload.
+- In order to introduce the SMT-alignment check in CPU Manager, we introduce a new flag in Kubelet to allow the user to specify `cpumanager-policy-options` which when specified with `full-pcpus-only` as its value provides the capability to modify the behaviour of static policy to strictly guarantee allocation of whole cores to a workload.
 - The `CPUManagerPolicyOptions` received from the kubelet config/command line args is propogated to the Container Manager.
 - The responsibility of admission control is centralized in containermanager. The resource managers and/or the resource allocation orchestrator (Topology Manager) still have the responsibility of running the checks to admit the pods, but the handling of these errors and the building of the pod lifecycle result are now factored in containermanager.
 - Prior to this feature, the Container Manager admission handler was delegated to the topology manager if the latter was enabled. This worked well under the assumption that only Topology Manager had the ability to reject admissions with pods. But with the introduction of this feature, the CPU Manager also needs the ability to possibly reject pods if strict SMT alignment is requested. In order to do so, we introduce a new error and let it drive the rejection. Due to an already existing dependency between CPUManager and TopologyManager as the former imports the latter in order to support the `topologymanager.HintProvider` interface, container manager is considered as the appropriate for performing admission control.
-- When `reject-non-smt-aligned` policy option is specified along with `static` CPU Manager policy, an additional check in the allocation logic of the `static` policy ensures that CPUs would be allocated such that full cores are allocated. Because of this check, a pod would never have to acquire single threads with the aim to fill partially-allocated cores.
+- When `full-pcpus-only` policy option is specified along with `static` CPU Manager policy, an additional check in the allocation logic of the `static` policy ensures that CPUs would be allocated such that full cores are allocated. Because of this check, a pod would never have to acquire single threads with the aim to fill partially-allocated cores.
 - In case request translates to partial occupancy of the cores, the Pod will not be admitted and would fail with `SMTAlignmentError`.
 
 
 ### Resource Accounting
 
-To illustrate the behaviour of the `reject-non-smt-aligned` policy option, we will consider the following CPU topology. We will use as example a CPU package with 16 physical cores, 2-way SMT-capable.
+To illustrate the behaviour of the `full-pcpus-only` policy option, we will consider the following CPU topology. We will use as example a CPU package with 16 physical cores, 2-way SMT-capable.
 
 ![Example Topology](smtalign-topology.png)
 
@@ -162,11 +162,11 @@ spec:
         cpu: "5"
 ```
 
-The `reject-non-smt-aligned` policy option will cause the pod to be rejected since it doesn't request enough cores to consume all virtual threads exposed by the CPU.
+The `full-pcpus-only` policy option will cause the pod to be rejected since it doesn't request enough cores to consume all virtual threads exposed by the CPU.
 
  would need to make sure the remaining core on the half-allocated physical CPU is left unallocated to avoid noisy neighbours.
 
-![Example core allocation with the reject-non-smt-aligned policy option when requesting a odd number of cores](smtalign-allocation-odd-cores.png)
+![Example core allocation with the full-pcpus-only policy option when requesting a odd number of cores](smtalign-allocation-odd-cores.png)
 
 The container will then actually get more virtual cores (6) than what is requesting (5).
 
@@ -250,7 +250,7 @@ We would like to mention a further extension of this work, which we are *not* pr
 A further subset of the latency sensitive class of workload we identified (CNF, HFT) benefits most of non-SMT system, delivering the best possible performance here.
 For these applications, just disabling SMT at machine level solves the need of the workload, but overall creates worse usage of hardware resources and poorer container density.
 
-Another policy option, or a further refinement of `reject-non-smt-aligned`, which enables non-SMT emulation on SMT-enabled system would allow to accommodate these needs, but this would cause even more significant resource accounting mismatches
+Another policy option, or a further refinement of `full-pcpus-only`, which enables non-SMT emulation on SMT-enabled system would allow to accommodate these needs, but this would cause even more significant resource accounting mismatches
 as described above. Furthermore, at the moment of writing we are still assessing how large is the set of the classes which benefit of these extra guarantees.
 
 For all these reasons we postponed this work to a later date.
@@ -268,6 +268,7 @@ The [implementation PR](https://github.com/kubernetes/kubernetes/pull/101432) wi
 #### Alpha to Beta Graduation
 - [X] Gather feedback from the consumer of the policy.
 - [X] No major bugs reported in the previous cycle.
+- [X] Use of this policy option to further configure the behavior of CPU manager. Another CPUManager policy option `distribute-cpus-across-numa` is being proposed in 1.23 release to distribute CPUs across NUMA nodes instead of packing them.
 
 #### Beta to G.A Graduation
 - [X] Allowing time for feedback (1 year).
@@ -332,7 +333,7 @@ No changes needed
 ### Troubleshooting
 
 * **How does this feature react if the API server and/or etcd is unavailable?**: No effect.
-* **What are other known failure modes?** TBD
+* **What are other known failure modes?** No known failure mode.
 * **What steps should be taken if SLOs are not being met to determine the problem?** N/A
 
 [supported limits]: https://git.k8s.io/community//sig-scalability/configs-and-limits/thresholds.md
@@ -349,3 +350,4 @@ No changes needed
 - 2021-05-10: KEP update to add to rename the `smtalign` to `reject-non-smt-aligned` for better clarity and address review comments
 - 2021-05-11: KEP update to add to the `configurable` alias and address review comments
 - 2021-05-13: KEP update to postpone the `configurable` alias, per review comments
+- 2021-09-02: KEP update to capture the policy name `full-pcpus-only` based on the implementation merged in 1.22, explain how this feature is being used for introduction of another policy option and updates pertaining to promotion of the feature to Beta.
diff --git a/keps/sig-node/2625-cpumanager-policies-thread-placement/kep.yaml b/keps/sig-node/2625-cpumanager-policies-thread-placement/kep.yaml
@@ -7,6 +7,7 @@ owning-sig: sig-node
 participating-sigs: []
 status: implementable
 creation-date: "2021-04-14"
+last-updated: "2021-09-02"
 reviewers:
   - "@klueska"
 approvers:
@@ -17,12 +18,12 @@ see-also: []
 replaces: []
 
 # The target maturity stage in the current dev cycle for this KEP.
-stage: alpha
+stage: beta
 
 # The most recent milestone for which work toward delivery of this KEP has been
 # done. This can be the current (upcoming) milestone, if it is being actively
 # worked on.
-latest-milestone: "v1.22"
+latest-milestone: "v1.23"
 
 # The milestone at which this feature was, or is targeted to be, at each stage.
 milestone:
