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Scheduling virtual machines

You can schedule a virtual machine (VM) on a node by ensuring that the VM’s CPU model and policy attribute are matched for compatibility with the CPU models and policy attributes supported by the node.

Understanding policy attributes

You can schedule a virtual machine (VM) by specifying a policy attribute and a CPU feature that is matched for compatibility when the VM is scheduled on a node. A policy attribute specified for a VM determines how that VM is scheduled on a node.

Policy attribute Description

force

The VM is forced to be scheduled on a node. This is true even if the host CPU does not support the VM’s CPU.

require

Default policy that applies to a VM if the VM is not configured with a specific CPU model and feature specification. If a node is not configured to support CPU node discovery with this default policy attribute or any one of the other policy attributes, VMs are not scheduled on that node. Either the host CPU must support the VM’s CPU or the hypervisor must be able to emulate the supported CPU model.

optional

The VM is added to a node if that VM is supported by the host’s physical machine CPU.

disable

The VM cannot be scheduled with CPU node discovery.

forbid

The VM is not scheduled even if the feature is supported by the host CPU and CPU node discovery is enabled.

Setting a policy attribute and CPU feature

You can set a policy attribute and CPU feature for each virtual machine (VM) to ensure that it is scheduled on a node according to policy and feature. The CPU feature that you set is verified to ensure that it is supported by the host CPU or emulated by the hypervisor.

Procedure

  • Edit the domain spec of your VM configuration file. The following example sets the CPU feature and the require policy for a virtual machine instance (VMI):

    apiVersion: kubevirt.io/v1
kind: VirtualMachine
metadata:
  name: myvmi
spec:
  domain:
    cpu:
      features:
      - name: apic (1)
        policy: require (2)
    1 Name of the CPU feature for the VM or VMI.
    2 Policy attribute for the VM or VMI.

Scheduling virtual machines with the supported CPU model

You can configure a CPU model for a virtual machine (VM) or a virtual machine instance (VMI) to schedule it on a node where its CPU model is supported.

Procedure

  • Edit the domain spec of your virtual machine configuration file. The following example shows a specific CPU model defined for a VMI:

    apiVersion: kubevirt.io/v1
kind: VirtualMachineInstance
metadata:
  name: myvmi
spec:
  domain:
    cpu:
      model: Conroe (1)
    1 CPU model for the VMI.

Scheduling virtual machines with the host model

When the CPU model for a virtual machine (VM) is set to host-model, the VM inherits the CPU model of the node where it is scheduled.

Procedure

  • Edit the domain spec of your VM configuration file. The following example shows host-model being specified for the virtual machine instance (VMI):

    apiVersion: kubevirt/v1alpha3
kind: VirtualMachineInstance
metadata:
  name: myvmi
spec:
  domain:
    cpu:
      model: host-model (1)
    1 The VM or VMI that inherits the CPU model of the node where it is scheduled.