Bug 513295

Summary:	Frame drops when using applications with CPU rendering
Product:	[Plasma] kwin	Reporter:	thesword <thesword53>
Component:	performance	Assignee:	KWin default assignee <kwin-bugs-null>
Status:	REPORTED ---
Severity:	normal	CC:	nate
Priority:	NOR	Keywords:	efficiency-and-performance, wayland-only
Version First Reported In:	6.5.4
Target Milestone:	---
Platform:	Other
OS:	Linux
See Also:	https://bugs.kde.org/show_bug.cgi?id=479250 https://bugs.kde.org/show_bug.cgi?id=515887
Latest Commit:		Version Fixed/Implemented In:
Sentry Crash Report:

Description thesword 2025-12-13 15:23:20 UTC

When the content of an application without GPU acceleration is updated, the whole kwin_wayland process will drop frames. It seems that the video output those applications are copied from CPU to GPU, but this slow operation happens on the main thread and blocks other things, such as input handling.

STEPS TO REPRODUCE
1. Open dolphin file explorer on a high resolution screen with high refresh rate 3840x2160 120 Hz or 2560x1440 240 Hz.
2. Move the mouse while selecting files

OBSERVED RESULT
Kwin is dropping frame and using almost 100% of 1 CPU thread

EXPECTED RESULT
Only dolphin should drop frames, not kwin

SOFTWARE/OS VERSIONS
Linux: 6.17.9-arch1-1
KDE Plasma Version: 6.5.4
KDE Frameworks Version: 6.20.0
Qt Version: 6.10.1

ADDITIONAL INFORMATION
I'm using 2560x1440 360Hz and 2560x1440 144Hz monitors
This issue is only observable on Wayland, not on X11

Comment 1 Nate Graham 2025-12-16 22:31:57 UTC

> Only dolphin should drop frames, not kwin
FWIW KWin is still responsible for drawing the window, even if software rendering is in use.

Comment 2 thesword 2026-01-08 19:30:32 UTC

Yes but an application using software rendering shouldn't slowdown the whole desktop, including keyboard and mouse inputs and other applications using GPU rendering.