Chapter 8. Using CPU Manager and Topology Manager CPU Manager manages groups of CPUs and constrains workloads to specific CPUs. CPU Manager is useful for workloads that have some of these attributes: Require as much CPU time as possible. Are sensitive to processor cache misses. Are low-latency network applications. Coordinate with other processes and benefit from sharing a single processor cache. Topology Manager collects hints from the CPU Manager, Device Manager, and other Hint Providers to align pod resources, such as CPU, SR-IOV VFs, and other device resources, for all Quality of Service (QoS) classes on the same non-uniform memory access (NUMA) node. Topology Manager uses topology information from the collected hints to decide if a pod can be accepted or rejected on a node, based on the configured Topology Manager policy and pod resources requested. Topology Manager is useful for workloads that use hardware accelerators to support latency-critical execution and high throughput parallel computation. To use Topology Manager you must configure CPU Manager with the static policy. 8.1. Setting up CPU Manager Procedure Optional: Label a node: # oc label node perf-node.example.com cpumanager=true Edit the MachineConfigPool of the nodes where CPU Manager should be enabled. In this example, all workers have CPU Manager enabled: # oc edit machineconfigpool worker Add a label to the worker machine config pool: metadata: creationTimestamp: 2020-xx-xxx generation: 3 labels: custom-kubelet: cpumanager-enabled Create a KubeletConfig , cpumanager-kubeletconfig.yaml , custom resource (CR). Refer to the label created in the step to have the correct nodes updated with the new kubelet config. See the machineConfigPoolSelector section: apiVersion: machineconfiguration.openshift.io/v1 kind: KubeletConfig metadata: name: cpumanager-enabled spec: machineConfigPoolSelector: matchLabels: custom-kubelet: cpumanager-enabled kubeletConfig: cpuManagerPolicy: static 1 cpuManagerReconcilePeriod: 5s 2 1 Specify a policy: none . This policy explicitly enables the existing default CPU affinity scheme, providing no affinity beyond what the scheduler does automatically. This is the default policy. static . This policy allows containers in guaranteed pods with integer CPU requests. It also limits access to exclusive CPUs on the node. If static , you must use a lowercase s . 2 Optional. Specify the CPU Manager reconcile frequency. The default is 5s . Create the dynamic kubelet config: # oc create -f cpumanager-kubeletconfig.yaml This adds the CPU Manager feature to the kubelet config and, if needed, the Machine Config Operator (MCO) reboots the node. To enable CPU Manager, a reboot is not needed. Check for the merged kubelet config: # oc get machineconfig 99-worker-XXXXXX-XXXXX-XXXX-XXXXX-kubelet -o json | grep ownerReference -A7 Example output "ownerReferences": [ { "apiVersion": "machineconfiguration.openshift.io/v1", "kind": "KubeletConfig", "name": "cpumanager-enabled", "uid": "7ed5616d-6b72-11e9-aae1-021e1ce18878" } ] Check the worker for the updated kubelet.conf : # oc debug node/perf-node.example.com sh-4.2# cat /host/etc/kubernetes/kubelet.conf | grep cpuManager Example output cpuManagerPolicy: static 1 cpuManagerReconcilePeriod: 5s 2 1 cpuManagerPolicy is defined when you create the KubeletConfig CR. 2 cpuManagerReconcilePeriod is defined when you create the KubeletConfig CR. Create a pod that requests a core or multiple cores. Both limits and requests must have their CPU value set to a whole integer. That is the number of cores that will be dedicated to this pod: # cat cpumanager-pod.yaml Example output apiVersion: v1 kind: Pod metadata: generateName: cpumanager- spec: containers: - name: cpumanager image: gcr.io/google_containers/pause:3.2 resources: requests: cpu: 1 memory: "1G" limits: cpu: 1 memory: "1G" nodeSelector: cpumanager: "true" Create the pod: # oc create -f cpumanager-pod.yaml Verify that the pod is scheduled to the node that you labeled: # oc describe pod cpumanager Example output Name: cpumanager-6cqz7 Namespace: default Priority: 0 PriorityClassName: <none> Node: perf-node.example.com/xxx.xx.xx.xxx ... Limits: cpu: 1 memory: 1G Requests: cpu: 1 memory: 1G ... QoS Class: Guaranteed Node-Selectors: cpumanager=true Verify that the cgroups are set up correctly. Get the process ID (PID) of the pause process: # ├─init.scope │ └─1 /usr/lib/systemd/systemd --switched-root --system --deserialize 17 └─kubepods.slice ├─kubepods-pod69c01f8e_6b74_11e9_ac0f_0a2b62178a22.slice │ ├─crio-b5437308f1a574c542bdf08563b865c0345c8f8c0b0a655612c.scope │ └─32706 /pause Pods of quality of service (QoS) tier Guaranteed are placed within the kubepods.slice . Pods of other QoS tiers end up in child cgroups of kubepods : # cd /sys/fs/cgroup/cpuset/kubepods.slice/kubepods-pod69c01f8e_6b74_11e9_ac0f_0a2b62178a22.slice/crio-b5437308f1ad1a7db0574c542bdf08563b865c0345c86e9585f8c0b0a655612c.scope # for i in `ls cpuset.cpus tasks` ; do echo -n "USDi "; cat USDi ; done Example output cpuset.cpus 1 tasks 32706 Check the allowed CPU list for the task: # grep ^Cpus_allowed_list /proc/32706/status Example output Cpus_allowed_list: 1 Verify that another pod (in this case, the pod in the burstable QoS tier) on the system cannot run on the core allocated for the Guaranteed pod: # cat /sys/fs/cgroup/cpuset/kubepods.slice/kubepods-besteffort.slice/kubepods-besteffort-podc494a073_6b77_11e9_98c0_06bba5c387ea.slice/crio-c56982f57b75a2420947f0afc6cafe7534c5734efc34157525fa9abbf99e3849.scope/cpuset.cpus 0 # oc describe node perf-node.example.com Example output ... Capacity: attachable-volumes-aws-ebs: 39 cpu: 2 ephemeral-storage: 124768236Ki hugepages-1Gi: 0 hugepages-2Mi: 0 memory: 8162900Ki pods: 250 Allocatable: attachable-volumes-aws-ebs: 39 cpu: 1500m ephemeral-storage: 124768236Ki hugepages-1Gi: 0 hugepages-2Mi: 0 memory: 7548500Ki pods: 250 ------- ---- ------------ ---------- --------------- ------------- --- default cpumanager-6cqz7 1 (66%) 1 (66%) 1G (12%) 1G (12%) 29m Allocated resources: (Total limits may be over 100 percent, i.e., overcommitted.) Resource Requests Limits -------- -------- ------ cpu 1440m (96%) 1 (66%) This VM has two CPU cores. The system-reserved setting reserves 500 millicores, meaning that half of one core is subtracted from the total capacity of the node to arrive at the Node Allocatable amount. You can see that Allocatable CPU is 1500 millicores. This means you can run one of the CPU Manager pods since each will take one whole core. A whole core is equivalent to 1000 millicores. If you try to schedule a second pod, the system will accept the pod, but it will never be scheduled: NAME READY STATUS RESTARTS AGE cpumanager-6cqz7 1/1 Running 0 33m cpumanager-7qc2t 0/1 Pending 0 11s 8.2. Topology Manager policies Topology Manager aligns Pod resources of all Quality of Service (QoS) classes by collecting topology hints from Hint Providers, such as CPU Manager and Device Manager, and using the collected hints to align the Pod resources. Topology Manager supports four allocation policies, which you assign in the KubeletConfig custom resource (CR) named cpumanager-enabled : none policy This is the default policy and does not perform any topology alignment. best-effort policy For each container in a pod with the best-effort topology management policy, kubelet calls each Hint Provider to discover their resource availability. Using this information, the Topology Manager stores the preferred NUMA Node affinity for that container. If the affinity is not preferred, Topology Manager stores this and admits the pod to the node. restricted policy For each container in a pod with the restricted topology management policy, kubelet calls each Hint Provider to discover their resource availability. Using this information, the Topology Manager stores the preferred NUMA Node affinity for that container. If the affinity is not preferred, Topology Manager rejects this pod from the node, resulting in a pod in a Terminated state with a pod admission failure. single-numa-node policy For each container in a pod with the single-numa-node topology management policy, kubelet calls each Hint Provider to discover their resource availability. Using this information, the Topology Manager determines if a single NUMA Node affinity is possible. If it is, the pod is admitted to the node. If a single NUMA Node affinity is not possible, the Topology Manager rejects the pod from the node. This results in a pod in a Terminated state with a pod admission failure. 8.3. Setting up Topology Manager To use Topology Manager, you must configure an allocation policy in the KubeletConfig custom resource (CR) named cpumanager-enabled . This file might exist if you have set up CPU Manager. If the file does not exist, you can create the file. Prerequisites Configure the CPU Manager policy to be static . Procedure To activate Topology Manager: Configure the Topology Manager allocation policy in the custom resource. USD oc edit KubeletConfig cpumanager-enabled apiVersion: machineconfiguration.openshift.io/v1 kind: KubeletConfig metadata: name: cpumanager-enabled spec: machineConfigPoolSelector: matchLabels: custom-kubelet: cpumanager-enabled kubeletConfig: cpuManagerPolicy: static 1 cpuManagerReconcilePeriod: 5s topologyManagerPolicy: single-numa-node 2 1 This parameter must be static with a lowercase s . 2 Specify your selected Topology Manager allocation policy. Here, the policy is single-numa-node . Acceptable values are: default , best-effort , restricted , single-numa-node . 8.4. Pod interactions with Topology Manager policies The example Pod specs below help illustrate pod interactions with Topology Manager. The following pod runs in the BestEffort QoS class because no resource requests or limits are specified. spec: containers: - name: nginx image: nginx The pod runs in the Burstable QoS class because requests are less than limits. spec: containers: - name: nginx image: nginx resources: limits: memory: "200Mi" requests: memory: "100Mi" If the selected policy is anything other than none , Topology Manager would not consider either of these Pod specifications. The last example pod below runs in the Guaranteed QoS class because requests are equal to limits. spec: containers: - name: nginx image: nginx resources: limits: memory: "200Mi" cpu: "2" example.com/device: "1" requests: memory: "200Mi" cpu: "2" example.com/device: "1" Topology Manager would consider this pod. The Topology Manager would consult the hint providers, which are CPU Manager and Device Manager, to get topology hints for the pod. Topology Manager will use this information to store the best topology for this container. In the case of this pod, CPU Manager and Device Manager will use this stored information at the resource allocation stage.

Commands:
oc label node perf-node.example.com cpumanager=true
oc edit machineconfigpool worker
metadata: creationTimestamp: 2020-xx-xxx generation: 3 labels: custom-kubelet: cpumanager-enabled
apiVersion: machineconfiguration.openshift.io/v1 kind: KubeletConfig metadata: name: cpumanager-enabled spec: machineConfigPoolSelector: matchLabels: custom-kubelet: cpumanager-enabled kubeletConfig: cpuManagerPolicy: static 1 cpuManagerReconcilePeriod: 5s 2
oc create -f cpumanager-kubeletconfig.yaml
oc get machineconfig 99-worker-XXXXXX-XXXXX-XXXX-XXXXX-kubelet -o json | grep ownerReference -A7
"ownerReferences": [ { "apiVersion": "machineconfiguration.openshift.io/v1", "kind": "KubeletConfig", "name": "cpumanager-enabled", "uid": "7ed5616d-6b72-11e9-aae1-021e1ce18878" } ]
oc debug node/perf-node.example.com sh-4.2# cat /host/etc/kubernetes/kubelet.conf | grep cpuManager
cpuManagerPolicy: static 1 cpuManagerReconcilePeriod: 5s 2
cat cpumanager-pod.yaml
apiVersion: v1 kind: Pod metadata: generateName: cpumanager- spec: containers: - name: cpumanager image: gcr.io/google_containers/pause:3.2 resources: requests: cpu: 1 memory: "1G" limits: cpu: 1 memory: "1G" nodeSelector: cpumanager: "true"
oc create -f cpumanager-pod.yaml
oc describe pod cpumanager
Name: cpumanager-6cqz7 Namespace: default Priority: 0 PriorityClassName: <none> Node: perf-node.example.com/xxx.xx.xx.xxx Limits: cpu: 1 memory: 1G Requests: cpu: 1 memory: 1G QoS Class: Guaranteed Node-Selectors: cpumanager=true
├─init.scope │ └─1 /usr/lib/systemd/systemd --switched-root --system --deserialize 17 └─kubepods.slice ├─kubepods-pod69c01f8e_6b74_11e9_ac0f_0a2b62178a22.slice │ ├─crio-b5437308f1a574c542bdf08563b865c0345c8f8c0b0a655612c.scope │ └─32706 /pause
cd /sys/fs/cgroup/cpuset/kubepods.slice/kubepods-pod69c01f8e_6b74_11e9_ac0f_0a2b62178a22.slice/crio-b5437308f1ad1a7db0574c542bdf08563b865c0345c86e9585f8c0b0a655612c.scope for i in `ls cpuset.cpus tasks` ; do echo -n "USDi "; cat USDi ; done
cpuset.cpus 1 tasks 32706
grep ^Cpus_allowed_list /proc/32706/status
Cpus_allowed_list: 1
cat /sys/fs/cgroup/cpuset/kubepods.slice/kubepods-besteffort.slice/kubepods-besteffort-podc494a073_6b77_11e9_98c0_06bba5c387ea.slice/crio-c56982f57b75a2420947f0afc6cafe7534c5734efc34157525fa9abbf99e3849.scope/cpuset.cpus 0 oc describe node perf-node.example.com
Capacity: attachable-volumes-aws-ebs: 39 cpu: 2 ephemeral-storage: 124768236Ki hugepages-1Gi: 0 hugepages-2Mi: 0 memory: 8162900Ki pods: 250 Allocatable: attachable-volumes-aws-ebs: 39 cpu: 1500m ephemeral-storage: 124768236Ki hugepages-1Gi: 0 hugepages-2Mi: 0 memory: 7548500Ki pods: 250 ------- ---- ------------ ---------- --------------- ------------- --- default cpumanager-6cqz7 1 (66%) 1 (66%) 1G (12%) 1G (12%) 29m Allocated resources: (Total limits may be over 100 percent, i.e., overcommitted.) Resource Requests Limits -------- -------- ------ cpu 1440m (96%) 1 (66%)
NAME READY STATUS RESTARTS AGE cpumanager-6cqz7 1/1 Running 0 33m cpumanager-7qc2t 0/1 Pending 0 11s
oc edit KubeletConfig cpumanager-enabled
apiVersion: machineconfiguration.openshift.io/v1 kind: KubeletConfig metadata: name: cpumanager-enabled spec: machineConfigPoolSelector: matchLabels: custom-kubelet: cpumanager-enabled kubeletConfig: cpuManagerPolicy: static 1 cpuManagerReconcilePeriod: 5s topologyManagerPolicy: single-numa-node 2
spec: containers: - name: nginx image: nginx
spec: containers: - name: nginx image: nginx resources: limits: memory: "200Mi" requests: memory: "100Mi"
spec: containers: - name: nginx image: nginx resources: limits: memory: "200Mi" cpu: "2" example.com/device: "1" requests: memory: "200Mi" cpu: "2" example.com/device: "1"