Bug 509877

Summary:	Occasional jerkiness with AMD graphics on 6.4.90
Product:	[Plasma] kwin	Reporter:	Michael Marley <michael>
Component:	performance	Assignee:	KWin default assignee <kwin-bugs-null>
Status:	RESOLVED UPSTREAM
Severity:	normal	CC:	michael, nate, xaver.hugl
Priority:	NOR	Keywords:	efficiency-and-performance, regression
Version First Reported In:	6.4.90
Target Milestone:	---
Platform:	Kubuntu
OS:	Linux
Latest Commit:		Version Fixed In:
Sentry Crash Report:

Description Michael Marley 2025-09-24 17:31:13 UTC

SUMMARY
After upgrading to Plasma 6.4.90, I have noticed that I randomly but rather often seem to get jerkiness or framerate drops to 30fps for a few seconds which are usually most noticeable due to jerky mouse cursor movement.  This seems to happen most often after opening new windows, particularly Firefox windows.  I've only noticed this on a PC with AMD graphics; I cannot seem to reproduce it with Intel graphics.  It also seems to happen less severely if I put the GPU in "game mode" in the UEFI config (which just increases the static VRAM allocation).

For reference, the system is a Framework 13 laptop with the AMD 7840 processor and the 780m GPU.  I reproduced the issue while driving a single 3840x2160p60 monitor.  With Plasma 6.4.5, I never saw this behavior and everything was always smooth.

STEPS TO REPRODUCE
1. Run kwin 6.4.90 on a system with AMD integrated graphics in "auto" memory allocation mode
2. Open and close Firefox windows
3. Wave the mouse around for a bit after opening/closing each window

OBSERVED RESULT
Often frames will drop or the framerate will drop to 30fps for a few seconds.

EXPECTED RESULT
The framerate should remain at 60fps without dropping frames.

SOFTWARE/OS VERSIONS
Linux: 6.17.0-061700rc7
KDE Plasma Version: 6.4.90
KDE Frameworks Version: 6.18.0
Qt Version: 6.9.2

Comment 1 Zamundaaa 2025-09-25 00:58:26 UTC

Does putting KWIN_USE_OVERLAYS=0 into /etc/environment and rebooting help?

Comment 2 Michael Marley 2025-09-25 01:06:06 UTC

Yes, that seems to clear it up.

Comment 3 Zamundaaa 2025-09-26 14:52:32 UTC

Okay, then this is most likely https://gitlab.freedesktop.org/drm/amd/-/issues/4358. In the final 6.5 release, overlays are already set to be off by default to avoid driver bugs like that.

It's interesting that the preallocated ram for the GPU changes anything, not sure what that's about. Either way, it would be good to add your information about this to the issue as well.

Comment 4 Michael Marley 2025-09-26 15:49:43 UTC

Thanks, that sounds exactly like what I'm experiencing.  I did some more testing regarding the RAM allocation and found that my initial impression was just a red herring; now I don't think that has any impact.