utmapp
Severe VM performance degradation after sleep, FaceTime call, or audio output change (macOS 15.5 beta 2, M2 MacBook Air, UTM 4.6.4)
When running a Windows 11 virtual machine in UTM (version 4.6.4) for over an hour, the system gradually becomes less responsive. The issue becomes significantly worse in the following scenarios:
- After the MacBook is put to sleep and then woken up.
- After answering and ending a FaceTime or cellular call on the Mac.
- After changing audio output — for example, switching from AirPods Pro 2 back to the Mac's internal speakers. In these cases, the VM becomes extremely sluggish. The first sign is choppy, stuttering audio. Then keyboard input becomes severely delayed, with a lag of around 4–5 seconds per key press. Restarting the VM or the UTM app is the only way to temporarily restore responsiveness.
Steps To Reproduce:
- Launch a Windows 11 VM in UTM (version 4.6.4) on a MacBook Air M2 with 8 GB RAM.
- Use the VM for over an hour.
- Trigger one of the following events:
- Put the Mac to sleep and wake it up.
- Receive and end a FaceTime or cellular call.
- Connect and disconnect AirPods Pro 2, switching audio back to internal speakers.
- Observe performance degradation and audio stuttering.
Expected behavior:
The virtual machine should remain fully responsive regardless of the host’s sleep state, audio routing, or call activity. Host Machine:
- Device: MacBook Air with M2 chip
- RAM: 8 GB
- macOS version: Sequoia 15.5 beta 2 • UTM version: 4.6.4 Guest OS: Windows 11
Additional context:
This issue makes longer VM sessions unreliable. A restart of the VM helps temporarily, but the degradation returns after one of the listed events. I’d appreciate any fixes or workarounds — thank you for your work on this awesome project!
Additional info:
I’d like to provide some further observations based on extended testing and input from a friend who is also using UTM:
- The same performance issues occur on a MacBook Air with an M3 chip and 24 GB of RAM, which belongs to a friend of mine. So this is not limited to a lower-end configuration.
- On this M3 machine, my friend tested video games inside the VM, and the results were disappointing:
- Hearthstone runs very slowly and is barely playable.
- Heavier video games either don’t run at all or are completely unplayable.
- Battery life is also a concern — on my own M2 MacBook Air, running a Windows 11 VM via UTM results in the battery draining in about 6 hours, even with minimal background activity.
- There is noticeable lag during voice dictation on macOS when a VM is running — input becomes slow and unreliable inside the VM while dictating proces is finished.
- It’s worth noting that this is virtualization, not emulation, and both machines (my M2 and my friend's M3) are running Windows 11 for ARM VMs created from official ISO disk images provided by Microsoft.
These additional details show that performance limitations affect multiple setups and workflows. I hope this helps clarify the scope of the issue. Thanks again in advance for fixing all of these reported things.
One thing more.
The UTM version I reported the issue with (4.6.4) i've downloaded from the AppStore for Mac. I also installed a newer version (4.6.5) from Github, but this newer seems to be even less optimized, as I observed a drop in machine performance much more frequently and in a shorter time, after about 20-30 minutes.
Regardless of whether I assign 2 or 4 GB and my friend assigns 8 or 16, the virtual machine behaves similarly, with the same symptoms occurring.