Bug 513295 - Frame drops when using applications with CPU rendering
Summary: Frame drops when using applications with CPU rendering
Status: REPORTED
Alias: None
Product: kwin
Classification: Plasma
Component: performance (other bugs)
Version First Reported In: 6.5.4
Platform: Other Linux
: NOR normal
Target Milestone: ---
Assignee: KWin default assignee
URL:
Keywords: efficiency-and-performance, wayland-only
Depends on:
Blocks:
 
Reported: 2025-12-13 15:23 UTC by thesword
Modified: 2025-12-16 22:31 UTC (History)
1 user (show)

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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.