https://bugs.kde.org/show_bug.cgi?id=527948
Bug ID: 527948
Summary: KWin 6.8.1 on Wayland: low GPU performance despite
high GPU load, fixed by downgrading to 6.8.0
Classification: Plasma
Product: kwin
Version First 6.8.1
Reported In:
Platform: CachyOS
OS: Linux
Status: REPORTED
Severity: normal
Priority: NOR
Component: wayland-generic
Assignee: [email protected]
Reporter: [email protected]
Target Milestone: ---
SUMMARY
After updating Plasma from 6.8.0 to 6.8.1 (kwin 6.8.1-2.1, CachyOS build),
games
run with much worse performance than before. Downgrading only kwin to 6.8.0
fixes
it immediately. Booting a btrfs snapshot from before the update also fixes it.
STEPS TO REPRODUCE
1. Update Plasma 6.8.0 -> 6.8.1 on Wayland (update done 2026-10-24).
2. Start a game (MX Bikes, OpenGL; [other affected games]) with MangoHud.
3. Watch the frametime.
OBSERVED RESULT
Frametimes of roughly 14-20 ms (about 50-70 fps) in MangoHud, with the game
feeling slow. GPU usage is around 80%, CPU usage is low, and temperatures are
normal. It happens in every game I tried, not just one.
EXPECTED RESULT
The same performance as on KWin 6.8.0, where the system worked fine.
WHAT I RULED OUT
- Kernel: affected on both linux-cachyos (7.3.0-5) and linux-cachyos-lts
(6.18.55).
- GPU firmware: downgraded linux-firmware-amdgpu to 20260916-1, no change.
- Mesa: downgraded Mesa and lib32 packages from 26.2.5 to 26.2.4, no change.
- amd-ucode: same microcode revision before and after the update, so no change.
- GPU clocks: forcing power_dpm_force_performance_level=high, no change.
- Number of monitors: same with the second monitor disabled.
- Vsync: tried on and off, no improvement.
- Booting a pre-update snapshot (Mesa 26.2.4, kwin 6.8.0, firmware 20260916-1,
kernel 7.2.10): performance is normal.
- Downgrading only kwin 6.8.1-2.1 -> 6.8.0 on the otherwise-updated system:
performance is normal.
SYSTEM
- Distro: CachyOS (Arch-based), kwin package 6.8.1-2.1 (bad) / 6.8.0 (good)
- Session: Wayland
- GPU: AMD Radeon RX 9060 XT (RADV), Mesa 26.2.5 (also tested 26.2.4)
- Monitors: 2x 2560x1440@144 Hz (DP-2 and HDMI-A-1), VRR off, HDR off, scale 1
- Kernel: 7.3.0-5-cachyos and 6.18.55-2-cachyos-lts
- Third-party effect installed: better_blur_dx (kwin-effects-better-blur-dx).
On 6.8.1 it refused to load ("built for 6.8.0, expected 6.8.1"), so it was
not
active when the slowdown occurred. [Say whether you tested without it
installed.]
ADDITIONAL INFORMATION
Not yet tested: [X11 session on 6.8.1, other games or APIs, fullscreen vs
windowed]. I can provide more logs or test builds if needed.
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