QEMU uses CPU when Linux guest is idle

[proski]

brew config AND brew doctor output OR brew gist-logs <formula> link

> brew config && brew doctor
HOMEBREW_VERSION: 5.1.11-29-gf7c3d09
ORIGIN: https://github.com/Homebrew/brew
HEAD: f7c3d09a3d5c602a3107ac685f0a6d6468af196c
Last commit: 4 hours ago
Branch: main
Core tap JSON: 11 May 21:47 UTC
Core cask tap JSON: 11 May 21:47 UTC
HOMEBREW_PREFIX: /opt/homebrew
HOMEBREW_CASK_OPTS: []
HOMEBREW_DISPLAY: /var/run/com.apple.launchd.obcLyTor5X/org.xquartz:0
HOMEBREW_DOWNLOAD_CONCURRENCY: 28
HOMEBREW_EDITOR: nvim
HOMEBREW_FORBID_PACKAGES_FROM_PATHS: set
HOMEBREW_MAKE_JOBS: 14
HOMEBREW_SORBET_RUNTIME: set
Homebrew Ruby: 4.0.3 => /opt/homebrew/Library/Homebrew/vendor/portable-ruby/4.0.3/bin/ruby
CPU: 14-core 64-bit arm_brava
Clang: 21.0.0 build 2100
Git: 2.50.1 => /Library/Developer/CommandLineTools/usr/bin/git
Curl: 8.7.1 => /usr/bin/curl
macOS: 26.4.1-arm64
CLT: 26.5.0.0.1777544298
Xcode: N/A
Rosetta 2: false
Your system is ready to brew.

Verification

• My brew doctor output says Your system is ready to brew. and am still able to reproduce my issue.
• I ran brew update and am still able to reproduce my issue.
• I have resolved all warnings from brew doctor and that did not fix my problem.
• I searched for recent similar issues at https://github.com/Homebrew/homebrew-core/issues?q=is%3Aissue and found no duplicates.
• My issue is not about a failure to build a formula from source.

What were you trying to do (and why)?

I upgraded qemu from 10.2.1 to 11.0.0 on MacBook Pro M4 and discovered that CPU consumption on the host was about 900% for a 12-core emulated Linux machine, even when the VM wasn't doing anything. The laptop battery was discharging quickly. I stopped using qemu from homebrew and installed qemu 10.1.5 from nixos-darwin, which solved the issue.

I found the upstream issue today:
https://gitlab.com/qemu-project/qemu/-/work_items/3433

And here's the fix referenced in the issue:
https://patchew.org/QEMU/20260423170229.64655-1-philmd@linaro.org/20260423170229.64655-14-philmd@linaro.org/

Considering that Apple machines are specifically affected, would it be possible to make a patched qemu release for homebrew?

I hope the upstream makes a release soon, but there has been none at this time.

What happened (include all command output)?

900% CPU use on the host for 12-core Linux guess that was idle.

What did you expect to happen?

Less than 10% CPU use for idle Linux VMs.

Step-by-step reproduction instructions (by running brew commands)

brew update qemu

qemu-system-aarch64 \
	-run-with user=daemon \
	-smp cpus=12,sockets=1,cores=12,threads=1 \
	-m 32768 \
	-machine virt,gic-version=3 -cpu host -accel hvf \
	-nodefaults -nographic -vga none -audio none \
	-device virtio-net-pci,netdev=net0 -netdev user,id=net0,hostfwd=tcp::2022-:22 \
	-device virtio-rng-pci \
	-device virtio-blk-pci,drive=vda \
	-drive if=pflash,format=raw,file.filename=edk2-aarch64-code.fd,file.locking=off,readonly=on \
	-drive if=pflash,file.filename=/var/lib/vm/efi_vars.qcow2 \
	-drive if=none,media=disk,id=vda,file.filename=/var/lib/vm/n1.qcow2,discard=unmap,detect-zeroes=unmap

[SMillerDev]

I can't find that patch merged anywhere, can you find a commit for it?

[mediouni-m]

@SMillerDev it's in the target-arm push queue and will get to master after this weekend.

See https://patchew.org/QEMU/20260515104945.4145203-1-peter.maydell@linaro.org/20260515104945.4145203-24-peter.maydell@linaro.org/ and read the backporting notes

[cho-m]

QEMU 11.0.1 should have referenced commit

• qemu 11.0.1 #285005
• https://gitlab.com/qemu-project/qemu/-/commit/3b98370b55de7fff540092c1a6760726a6816625

[proski]

I've confirmed that qemu 11.0.1 installed by homebrew doesn't have this issue.