kubevirt cpu allocation ratio is ignored for provisioned virtual machines

Oct 13, 2025 by wbrum.org 123 views

kubevirt cpu allocation ratio is ignored for provisioned virtual machines

Kubevirt is a popular open-source platform for building and managing virtual machines (VMs) on Kubernetes. One of the key features of Kubevirt is its ability to provision and manage VMs with ease, making it a go-to choice for many organizations. However, as with any complex system, there are nuances and edge cases that can arise. In this article, we will explore a specific issue related to CPU allocation ratios in Kubevirt provisioned virtual machines.

CPU allocation ratios are a critical component of any cloud or virtualization environment. They determine how much CPU resources are allocated to a particular VM or workload. In Kubevirt, CPU allocation ratios are used to ensure that VMs are provisioned with the correct amount of CPU resources, taking into account the available resources on the underlying node.

The issue at hand is that Kubevirt ignores CPU allocation ratios for provisioned virtual machines. This is because the machine-controller sets requests and limits for CPU and memory resources of a Kubevirt virtual machine, which overrides the CPU allocation ratio calculation. This means that the CPU allocation ratio is not taken into account when provisioning a VM, leading to potential issues with CPU resource allocation.

To work around this issue, you need to configure the CPU resources in spec.domain.cpu instead of setting the requested CPU and limit in spec.domain.resources. This will allow Kubevirt to calculate the CPU requests for the launcher pod based on the configured CPU resources.

However, this approach has its own set of challenges. By configuring the CPU resources in spec.domain.cpu, you are essentially bypassing the machine-controller's request and limit settings. This means that no limit would be set to the launcher pod by default, which can lead to issues with CPU resource allocation.

To address this issue, you need to enable the CPU auto-limit feature in Kubevirt. This feature allows Kubevirt to automatically set CPU limits for the launcher pod based on the available CPU resources on the underlying node.

To enable the CPU auto-limit feature, you need to add labels to namespaces or apply resource quotas for namespaces. This will allow Kubevirt to automatically set CPU limits for the launcher pod, taking into account the available CPU resources on the underlying node.

As you can see, using the Kubevirt CPU allocation ratio feature requires additional configuration and setup. It would be beneficial to have a comprehensive documentation that outlines the requirements and steps to use this feature.

In conclusion, the Kubevirt CPU allocation ratio is ignored for provisioned virtual machines due to the machine-controller's request and limit settings. To work around this issue, you need to configure the CPU resources in spec.domain.cpu instead of setting the requested CPU and limit in spec.domain.resources. However, this approach has its own set of challenges, and you need to enable the CPU auto-limit feature to address these issues.

We hope that this article has provided valuable insights into the Kubevirt CPU allocation ratio issue and the steps required to work around it. We also hope that this article will serve as a catalyst for creating comprehensive documentation that outlines the requirements and steps to use the Kubevirt CPU allocation ratio feature.

Based on our analysis, we recommend the following:

Update the Kubevirt documentation to include information on the CPU allocation ratio feature and the steps required to use it.
Provide additional configuration options to allow users to customize the CPU allocation ratio feature.
Consider adding a warning or alert when the CPU allocation ratio feature is not enabled, to ensure that users are aware of the potential issues.

As Kubevirt continues to evolve and improve, we hope to see further enhancements to the CPU allocation ratio feature. Some potential areas for future work include:

Improving the CPU auto-limit feature to take into account additional factors, such as node affinity and anti-affinity.
Adding support for custom CPU allocation ratios, allowing users to define their own CPU allocation ratios for specific workloads.
Enhancing the Kubevirt documentation to provide more detailed information on the CPU allocation ratio feature and its usage.

By addressing these issues and enhancing the CPU allocation ratio feature, we can ensure that Kubevirt continues to provide a robust and reliable platform for building and managing virtual machines on Kubernetes.
kubevirt cpu allocation ratio is ignored for provisioned virtual machines: Q&A

In our previous article, we explored the issue of Kubevirt ignoring CPU allocation ratios for provisioned virtual machines. We also discussed the workaround of configuring CPU resources in spec.domain.cpu and the need to enable the CPU auto-limit feature. In this article, we will provide a Q&A section to address some of the most frequently asked questions related to this issue.

A: The CPU allocation ratio is a feature in Kubevirt that allows you to specify the percentage of CPU resources that can be allocated to a virtual machine (VM) on a node. This feature is used to ensure that VMs are provisioned with the correct amount of CPU resources, taking into account the available resources on the underlying node.

A: The CPU allocation ratio is ignored in Kubevirt because the machine-controller sets requests and limits for CPU and memory resources of a Kubevirt virtual machine, which overrides the CPU allocation ratio calculation. This means that the CPU allocation ratio is not taken into account when provisioning a VM, leading to potential issues with CPU resource allocation.

A: To configure the CPU resources in spec.domain.cpu, you need to update the spec.domain.cpu field in the VM configuration to specify the desired CPU resources. For example:

spec:
  domain:
    cpu:
      cores: 2
      threads: 2

This will configure the VM to use 2 CPU cores with 2 threads each.

A: The CPU auto-limit feature in Kubevirt is a feature that allows Kubevirt to automatically set CPU limits for the launcher pod based on the available CPU resources on the underlying node. This feature is used to prevent the launcher pod from consuming too much CPU resources and causing performance issues.

A: To enable the CPU auto-limit feature in Kubevirt, you need to add labels to namespaces or apply resource quotas for namespaces. For example:

apiVersion: v1
kind: Namespace
metadata:
  name: my-namespace
spec:
  labels:
    kubevirt.io/cpu-auto-limit: "true"

This will enable the CPU auto-limit feature for the my-namespace namespace.

A: The benefits of using the CPU auto-limit feature in Kubevirt include:

Improved performance: By automatically setting CPU limits, the CPU auto-limit feature helps to prevent the launcher pod from consuming too much CPU resources and causing performance issues.
Reduced resource utilization: By automatically setting CPU limits, the CPU auto-limit feature helps to reduce the amount of CPU resources consumed by the launcher pod, making it easier to manage resources.
Simplified management: By automatically setting CPU limits, the CPU auto-limit feature simplifies the management of CPU resources, making it easier to deploy and manage VMs.

A: The limitations of the CPU auto-limit feature in Kubevirt include:

Limited control: The CPU auto-limit feature provides limited control over CPU resource allocation, making it difficult to customize CPU resource allocation for specific workloads.
Complexity: The CPU auto-limit feature can add complexity to the deployment and management of VMs, making it difficult to troubleshoot issues.

In conclusion, the CPU allocation ratio is ignored in Kubevirt due to the machine-controller's request and limit settings. To work around this issue, you need to configure the CPU resources in spec.domain.cpu and enable the CPU auto-limit feature. We hope that this Q&A article has provided valuable insights into the CPU allocation ratio issue and the steps required to use the CPU auto-limit feature.