Ubuntu 24.04 KVM VM Degradation: QMD Interrupts

**Ubuntu 24.04 LTS Users Report Major Performance Degradation for Virtual Machines**

**[City, State] – [Date]** – Users who have recently upgraded to Ubuntu’s latest Long Term Support (LTS) release, 24.04 “Noble Numbat,” are reporting a significant and frustrating performance slowdown when managing virtual machines (VMs) using QEMU/KVM. The issue, which appears to be a regression from the prior 22.04.5 LTS version, is rendering VMs sluggish and, in some cases, nearly unusable.

Ubuntu 24.04 LTS, released on April 25, 2024, is designed to be a stable platform for years to come, making these early reports concerning for individuals and businesses relying on its virtualization capabilities. QEMU and KVM (Kernel-based Virtual Machine) are foundational open-source virtualization technologies on Linux, enabling users to run other operating systems like Windows 10 within their Ubuntu environment.

Reports emerging from community forums and bug trackers detail a consistent problem: virtual machines, particularly guests like Windows 10, exhibit extreme sluggishness and unresponsiveness. This occurs despite low actual disk activity, suggesting the bottleneck isn’t typical I/O.

Diagnostic checks performed by affected users point to unusually high CPU usage attributed to `qmd` (QEMU Monitor Device) interrupts. Specifically, examinations of `/proc/interrupts` reveal a disproportionate number of interrupts linked to `qmd-vm:monitor`, often saturating a single CPU core. This indicates a potential problem with how the new Ubuntu environment distributes or handles these critical system interrupts.

“It’s like hitting a brick wall,” commented one user on a tech forum, describing their Windows 10 VM’s performance. “On 22.04, it was smooth, but now on 24.04, it’s constantly bogged down by these ‘qmd’ interrupts, making even basic tasks unbearable.”

Attempts by users to mitigate the issue using standard Linux tools have largely proven ineffective. `irqbalance`, a utility designed to distribute interrupt load across multiple CPU cores, has failed to alleviate the problem. Similarly, configuring system tunables via `tuned` profiles has not yielded a solution. While `virt-manager` is a popular graphical frontend for managing these VMs, the core issue appears to lie deeper within the Ubuntu 24.04 LTS kernel or the QEMU packages themselves.

Users have confirmed that their kernel command-line parameters for `iommu` and `vfio-pci` pass-through, common for dedicated hardware access within VMs, are correctly configured, ruling out these common misconfigurations. The performance impact is not a minor inconvenience; it is significant enough to hinder typical workloads, with the `qmd` interrupts sometimes consuming an entire CPU core’s processing power.

The consensus among the growing number of users discussing the problem suggests a potential regression in the 24.04 LTS kernel or QEMU packages when compared to their predecessors on 22.04.5 LTS. This kind of regression in an LTS release is particularly problematic, as users expect enhanced stability and reliability over previous versions.

As of publishing, there has been no official statement from Canonical, the company behind Ubuntu, regarding the widespread reports. Users are encouraged to continue reporting their findings on platforms like the Ubuntu Community Forums and Launchpad bug tracker, providing detailed logs and system configurations to aid developers in identifying and resolving this critical performance issue. The timely resolution of this bug will be crucial for maintaining confidence in Ubuntu 24.04 LTS as a reliable platform for virtualization.