Chapter 7. Using CPU 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. 7.1. 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. static . This policy allows pods with certain resource characteristics to be granted increased CPU affinity and exclusivity on the node. 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 2 These settings were defined when you created 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-amd64:3.0 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

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-amd64:3.0 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