Tuning Windows VM Performance on SUSE Virtualization

SUSE Virtualization is a cloud native hyperconverged infrastructure platform solution optimized for running virtual machine and container workloads in the data center, multi-cloud and edge environments.

This article focuses on tuning Windows VM performance on SUSE Virtualization since Windows guests often need a little more care to reach their full potential. You can find the most impactful parameters to tune for Windows performance and the results.

Windows VM in SUSE Virtualization

SUSE Virtualization uses KubeVirt as the virtualization layer to manage virtual machines on Kubernetes. For instructions on creating and running Windows VMs on SUSE Virtualization, refer to the document Running Windows VMs on SUSE Virtualization. After creating a Windows VM, apply the tuning recommendations described in this document to optimize performance.

Drivers for the Windows VM

Windows is a popular guest OS for virtual machines, but it needs specific drivers to identify the block device, such as VirtIO/VirtIO SCSI. SUSE provides the VMDP (Virtual Machine Driver Pack for Microsoft Windows) for the Windows VM. For more details about how to install the driver, check the Installation Guide for VMDP.

Factors that affect Windows VM performance

There are several factors that can affect the performance of a Windows VM on SUSE Virtualization. Some of the most common ones include the choice of disk drivers, the CPU model, Hyper-V enlightenments and IOThreads. By tuning these parameters, you can significantly improve the performance of your Windows VM.

DISK Drivers

The most common disk driver for Windows VM is either VirtIO or VirtIO SCSI. The VirtIO driver is a paravirtualized driver that provides better performance. The VirtIO SCSI driver is used for the hotplug device. It can also perform well after tuning.

Here is the corresponding spec snippet for the disk device in the VM spec:

// For SCSI driver
devices:
  - disk:
      bus: scsi
    name: vol001

// For VirtIO driver
devices:
  - disk:
      bus: virtio
    name: vol001

We can see results for both drivers in the following table:

Performance

Latency

CPU Model

For the CPU model, we recommend the host-passthrough mode for optimal performance. This mode allows the VM to see the same CPU features as the host, which can improve performance for certain workloads.

Hyper-V enlightenments

Hyper-V enlightenments are a set of features that allow Windows to run more efficiently on a hypervisor. Enabling these features can improve performance by allowing Windows to better utilize the underlying hardware. KubeVirt also supports a set of Hyper-V enlightenments that can be enabled in the VM spec. Check the official document for more details.

Here is an example spec snippet for enabling Hyper-V enlightenments in the VM spec:

domain:
  clock:
    timer:
      hyperv: {}
  features:
    hyperv:
      ipi: {}
      relaxed: {}
      reset: {}
      runtime: {}
      spinlocks:
        spinlocks: 8191
      synic: {}
      synictimer: {}
      vapic: {}
      vpindex: {}

You can use “edit yaml” in the UI to edit the VM spec and add the above snippet to enable Hyper-V enlightenments. See the screenshot below for the UI operation:

Performance

Latency

IOThreads and MultiQueue

You can only use IOThreads with VirtIO. The SCSI device would be done with a SCSI controller, but currently, Kubevirt doesn’t support IOThreads for the SCSI controller.

IOThreads can improve performance for I/O intensive workloads by dedicating a thread to handle I/O operations. Kubevirt supports various IOThread Policies. Check the official document for more details.

In this article, we recommend using the supplementalPool policy and enabling Block Multi-Queue for better performance.

Here is an example spec snippet for enabling IOThreads and MultiQueue in the VM spec:

spec:
  domain:
    ioThreadsPolicy: supplementalPool
    ioThreads:
      SupplementalPoolThreadCount: 4
  devices:
    - disk:
        bus: virtio
      multiQueue: true
      name: vol001

Why didn’t we see a significant performance improvement after enabling IOThreads and MultiQueue? Because this test scenario has only one disk and no other disks to contend for the IOThread, the performance improvement is not significant. For scenarios with multiple disks, the performance improvement should be more noticeable.

Summary of the performance result:

Conclusion

The results show that choosing the right disk driver, enabling Hyper-V enlightenments, and using IOThreads can significantly improve the performance of a Windows VM on SUSE Virtualization. VirtIO and VirtIO SCSI give similar results once tuned. For multiple disks, VirtIO works better because it supports IOThreads and MultiQueue, offering higher performance. We recommend using VirtIO as the disk driver for Windows VMs on SUSE Virtualization and enabling Hyper-V enlightenments and IOThreads for best performance.

So, the following two combinations would be the best practice for the Windows VM performance tuning on SUSE Virtualization:

• VirtIO SCSI + Hyper-V enlightenments
• VirtIO + Hyper-V enlightenments + IOThreads

Appendix: Test Environment and Tool

Benchmark Tools: DISKSPD v2.2
Windows Version: Windows Server 2022
SUSE Virtualization Version: SUSE Virtualization 1.8.0
Kubevirt Version: Kubevirt 1.7.0
Longhorn Version: Longhorn v1.11.1
CPU: INTEL(R) XEON(R) SILVER 4509Y
SSD: VK000960KYDPT 960GB NVMe SSD