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Constraints

  • For processors using the AArch64 architecture, the specified VM chipset type (machine) needs to be virt-4.2 or a later version when a VM is created. For processors using the x86_64 architecture, the specified VM chipset type (machine) needs to be pc-i440fx-1.5 or a later version when a VM is created.
  • When configuring Guest NUMA, you need to configure the vCPUs that belong to the same socket in the same vNode. Otherwise, the VM may be soft locked up after the vCPUs are hot added, and the VM may fail to run properly.
  • VMs do not support vCPU hotplug during migration, hibernation, wakeup, or snapshot.
  • Whether the hot plugged vCPU can automatically go online depends on the VM OS logic rather than the virtualization layer.
  • When a VM is being started, stopped, or restarted, the hot plugged vCPU may become invalid. However, the hot plugged CPU takes effect after the VM is restarted.
  • When the vCPUs are hot added, if the number of added vCPUs is not an integer multiple of the number of cores in the VM vCPU topology configuration item, the vCPU topology displayed in the VM may be disordered. You are advised to add or remove vCPUs whose number is an integer multiple of the number of cores each time.
  • Feature enhancement: vCPU hotplug is already supported in earlier versions of openEuler (for example, openEuler 22.03 SP4). openEuler 24.03 LTS adds support to vCPU hot removal to adapt to more scenarios. However, the hotplug protocol has been modified in openEuler 24.03 LTS and is no longer compatible with earlier versions. This means that to utilize the vCPU hotplug feature, the guest kernel version must match the QEMU version on the host.
  • Hotplug specifications
    • The VM XML configuration file must contain the vcpu node as required by QEMU. This node is used to specify the number of vCPUs when a VM is started for the first time and the maximum number of vCPUs that can be reached through vCPU hot add.
    • vCPU hot add is restricted by the maximum number of CPUs supported by the hypervisor and guest OS. The specific restriction depends on the OS type.
Parent topic: Feature Description