第 6 章 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.
6.1. Setting up CPU Manager
Procedure
Optional: Label a node:
# oc label node perf-node.example.com cpumanager=true
Edit the
MachineConfigPoolof 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-enabledCreate a
KubeletConfig,cpumanager-kubeletconfig.yaml, custom resource (CR). Refer to the label created in the previous step to have the correct nodes updated with the new kubelet config. See themachineConfigPoolSelectorsection: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
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=trueVerify that the
cgroupsare set up correctly. Get the process ID (PID) of thepauseprocess:# ├─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
Guaranteedare placed within thekubepods.slice. Pods of other QoS tiers end up in childcgroupsofkubepods:# 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 "$i "; cat $i ; 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
burstableQoS tier) on the system cannot run on the core allocated for theGuaranteedpod:# 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-reservedsetting reserves 500 millicores, meaning that half of one core is subtracted from the total capacity of the node to arrive at theNode Allocatableamount. You can see thatAllocatable CPUis 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
