Black lives matter.
We stand in solidarity with the Black community.
Racism is unacceptable.
It conflicts with the core values of the Kubernetes project and our community does not tolerate it.
We stand in solidarity with the Black community.
Racism is unacceptable.
It conflicts with the core values of the Kubernetes project and our community does not tolerate it.
Kubernetes v1.18 [beta]
An increasing number of systems leverage a combination of CPUs and hardware accelerators to support latency-critical execution and high-throughput parallel computation. These include workloads in fields such as telecommunications, scientific computing, machine learning, financial services and data analytics. Such hybrid systems comprise a high performance environment.
In order to extract the best performance, optimizations related to CPU isolation, memory and device locality are required. However, in Kubernetes, these optimizations are handled by a disjoint set of components.
Topology Manager is a Kubelet component that aims to co-ordinate the set of components that are responsible for these optimizations.
You need to have a Kubernetes cluster, and the kubectl command-line tool must be configured to communicate with your cluster. If you do not already have a cluster, you can create one by using Minikube, or you can use one of these Kubernetes playgrounds:
Your Kubernetes server must be version v1.18. To check the version, enterkubectl version
.
Prior to the introduction of Topology Manager, the CPU and Device Manager in Kubernetes make resource allocation decisions independently of each other. This can result in undesirable allocations on multiple-socketed systems, performance/latency sensitive applications will suffer due to these undesirable allocations. Undesirable in this case meaning for example, CPUs and devices being allocated from different NUMA Nodes thus, incurring additional latency.
The Topology Manager is a Kubelet component, which acts as a source of truth so that other Kubelet components can make topology aligned resource allocation choices.
The Topology Manager provides an interface for components, called Hint Providers, to send and receive topology information. Topology Manager has a set of node level policies which are explained below.
The Topology manager receives Topology information from the Hint Providers as a bitmask denoting NUMA Nodes available and a preferred allocation indication. The Topology Manager policies perform a set of operations on the hints provided and converge on the hint determined by the policy to give the optimal result, if an undesirable hint is stored the preferred field for the hint will be set to false. In the current policies preferred is the narrowest preferred mask. The selected hint is stored as part of the Topology Manager. Depending on the policy configured the pod can be accepted or rejected from the node based on the selected hint. The hint is then stored in the Topology Manager for use by the Hint Providers when making the resource allocation decisions.
Support for the Topology Manager requires TopologyManager
feature gate to be enabled. It is enabled by default starting with Kubernetes 1.18.
The Topology Manager currently:
If these conditions are met, Topology Manager will align the requested resources.
Note: To align CPU resources with other requested resources in a Pod Spec, the CPU Manager should be enabled and proper CPU Manager policy should be configured on a Node. See control CPU Management Policies.
Topology Manager supports four allocation policies. You can set a policy via a Kubelet flag, --topology-manager-policy
.
There are four supported policies:
none
(default)best-effort
restricted
single-numa-node
This is the default policy and does not perform any topology alignment.
For each container in a Pod, the kubelet, with best-effort
topology
management policy, 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 will store this and admit the pod to the node anyway.
The Hint Providers can then use this information when making the resource allocation decision.
For each container in a Pod, the kubelet, with restricted
topology
management policy, 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 will reject this pod from the node. This will result in a pod in a Terminated
state with a pod admission failure.
Once the pod is in a Terminated
state, the Kubernetes scheduler will not attempt to reschedule the pod. It is recommended to use a ReplicaSet or Deployment to trigger a redeploy of the pod.
An external control loop could be also implemented to trigger a redeployment of pods that have the Topology Affinity
error.
If the pod is admitted, the Hint Providers can then use this information when making the resource allocation decision.
For each container in a Pod, the kubelet, with single-numa-node
topology
management policy, 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, Topology Manager will store this and the Hint Providers can then use this information when making the
resource allocation decision.
If, however, this is not possible then the Topology Manager will reject the pod from the node. This will result in a pod in a Terminated
state with a pod admission failure.
Once the pod is in a Terminated
state, the Kubernetes scheduler will not attempt to reschedule the pod. It is recommended to use a Deployment with replicas to trigger a redeploy of the Pod.
An external control loop could be also implemented to trigger a redeployment of pods that have the Topology Affinity
error.
Consider the containers in the following pod specs:
spec:
containers:
- name: nginx
image: nginx
This pod runs in the BestEffort
QoS class because no resource requests
or
limits
are specified.
spec:
containers:
- name: nginx
image: nginx
resources:
limits:
memory: "200Mi"
requests:
memory: "100Mi"
This pod runs in the Burstable
QoS class because requests are less than limits.
If the selected policy is anything other than none
, Topology Manager would consider these Pod specifications. The Topology Manager would consult the Hint Providers to get topology hints. In the case of the static
, the CPU Manager policy would return default topology hint, because these Pods do not have explicity request CPU resources.
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"
This pod with integer CPU request runs in the Guaranteed
QoS class because requests
are equal to limits
.
spec:
containers:
- name: nginx
image: nginx
resources:
limits:
memory: "200Mi"
cpu: "300m"
example.com/device: "1"
requests:
memory: "200Mi"
cpu: "300m"
example.com/device: "1"
This pod with sharing CPU request runs in the Guaranteed
QoS class because requests
are equal to limits
.
spec:
containers:
- name: nginx
image: nginx
resources:
limits:
example.com/deviceA: "1"
example.com/deviceB: "1"
requests:
example.com/deviceA: "1"
example.com/deviceB: "1"
This pod runs in the BestEffort
QoS class because there are no CPU and memory requests.
The Topology Manager would consider the above pods. The Topology Manager would consult the Hint Providers, which are CPU and Device Manager to get topology hints for the pods.
In the case of the Guaranteed
pod with integer CPU request, the static
CPU Manager policy would return topology hints relating to the exclusive CPU and the Device Manager would send back hints for the requested device.
In the case of the Guaranteed
pod with sharing CPU request, the static
CPU Manager policy would return default topology hint as there is no exclusive CPU request and the Device Manager would send back hints for the requested device.
In the above two cases of the Guaranteed
pod, the none
CPU Manager policy would return default topology hint.
In the case of the BestEffort
pod, the static
CPU Manager policy would send back the default topology hint as there is no CPU request and the Device Manager would send back the hints for each of the requested devices.
Using this information the Topology Manager calculates the optimal hint for the pod and stores this information, which will be used by the Hint Providers when they are making their resource assignments.
The maximum number of NUMA nodes that Topology Manager allows is 8. With more than 8 NUMA nodes there will be a state explosion when trying to enumerate the possible NUMA affinities and generating their hints.
The scheduler is not topology-aware, so it is possible to be scheduled on a node and then fail on the node due to the Topology Manager.
The Device Manager and the CPU Manager are the only components to adopt the Topology Manager's HintProvider interface. This means that NUMA alignment can only be achieved for resources managed by the CPU Manager and the Device Manager. Memory or Hugepages are not considered by the Topology Manager for NUMA alignment.