Resources requests and limits¶

In this document, we are talking about the resources values set on the virt-launcher compute container, referred to as "the container" below for simplicity.

CPU¶

Note: dedicated CPUs (and isolated emulator thread) are ignored here as they have a dedicated page.

CPU requests on the container¶

By default, the container requests (1/cpuAllocationRatio) CPU per vCPU. The number of vCPUs is socketscoresthreads, defaults to 1.
cpuAllocationRatio defaults to 10 but can be changed in the CR.
If a CPU limit is manually set on the VM(I) and no CPU request is, the CPU requests on the container will match the CPU limits
Manually setting CPU requests on the VM(I) will override all of the above and be the CPU requests for the container

CPU limits on the container¶

By default, no CPU limit is set on the container
If auto CPU limits is enabled (see next section), then the container will have a CPU limit of 1 per vCPU
Manually setting CPU limits on the VM(I) will override all of the above and be the CPU limits for the container

Auto CPU limits¶

For namespaces that require automatic CPU limits on VM(I)s, a label selector can be defined in the KubeVirt CR.
Once that label selector is defined, if a namespace matches the selector, all VM(I)s created in it will have a CPU limit of 1 per vCPU.

Example: - CR:

apiVersion: kubevirt.io/v1
kind: KubeVirt
metadata:
  name: kubevirt
  namespace: kubevirt
spec:
  configuration:
    autoCPULimitNamespaceLabelSelector:
      matchLabels:
        autoCpuLimit: "true"

- Namespace:

apiVersion: v1
kind: Namespace
metadata:
  labels:
    autoCpuLimit: "true"
    kubernetes.io/metadata.name: default
  name: default

Memory¶

Memory requests on the container¶

VM(I)s must specify a desired amount of memory, in either spec.domain.memory.guest or spec.domain.resources.requests.memory (ignoring hugepages, see the dedicated page). If both are set, the memory requests take precedence. A calculated amount of overhead will be added to it, forming the memory request value for the container.

Memory limits on the container¶

By default, no memory limit is set on the container
Manually setting a memory limit on the VM(I) will set the same value on the container

Warnings¶

Memory limits have to be more than memory requests + overhead, otherwise the container will have memory requests > limits and be rejected by Kubernetes.
Memory usage bursts could lead to VM crashes when memory limits are set