| Summary: | Moving cursor increases KWin's CPU usage, especially with higher refresh rate screens. | ||
|---|---|---|---|
| Product: | [Plasma] kwin | Reporter: | thesword <thesword53> |
| Component: | performance | Assignee: | KWin default assignee <kwin-bugs-null> |
| Status: | CONFIRMED --- | ||
| Severity: | normal | CC: | nate, xaver.hugl |
| Priority: | NOR | Keywords: | efficiency-and-performance, wayland-only |
| Version First Reported In: | 6.4.1 | ||
| Target Milestone: | --- | ||
| Platform: | Arch Linux | ||
| OS: | Linux | ||
| Latest Commit: | Version Fixed/Implemented In: | ||
| Sentry Crash Report: | |||
| Attachments: | Moving cursor in Gimp canvas | ||
I can also generally reproduce that moving the pointer increases KWin's CPU usage. I have a 120hz screen, and I can believe the effect is more noticeable with a screen that has triple the refresh rate. I can confirm that CPU usage is a tad high when moving the cursor in the Gimp canvas, but afaict that's just from constantly updating the window textures - scrolling in a similarly sized Dolphin window causes similar levels of CPU usage (though still less because Gimp doesn't support proper fractional scaling and thus uses a buffer with 2x size). I don't see any dropped frames on my 120Hz screen, but that could very well just come from texture uploads taking that long. I can't think of anything we can realistically do about it anytime soon if that's the case. I think the main issue is setting the cursor shape is done in the main thread ans blocks the process. In my case, it takes longer than the frametime which is 1/360s and this is why I see frame drops. I can reproduce this issue with more visible hitches when loading this page https://threejs.org/examples/webgl_renderer_pathtracer.html which loads the GPU at 100% and changing the cursor shape by hovering the URL bar. The root cause of this issue is the same as https://bugs.kde.org/show_bug.cgi?id=479250 |
Created attachment 182702 [details] Moving cursor in Gimp canvas When I move cursor inside GIMP or Inkscape canvas, kwin skips frames including cursor and uses much higher CPU (50% of 1 thread). This is noticeable on monitors with high refresh rate such as mine which has 360Hz. STEPS TO REPRODUCE 1. Open Gimp or Inkscape on a high refresh rate monitor (>= 240 Hz) 2. Open vkcube or glxgears on the same monitor with MangoHUD overlay 3. Move the cursor inside the canvas of Gimp or Inkscape OBSERVED RESULT MangoHUD overlay shows ~220-240 FPS and a non flat graph The cursor skips frames EXPECTED RESULT MangoHUD overlay shows 360FPS and a flat graph The cursor doesn't skip frames SOFTWARE/OS VERSIONS Linux 6.15.3-arch1-1 Plasma 6.4.1 CPU: AMD Ryzen 7 3700X GPU: Nvidia GeForce RTX 2080 SUPER ADDITIONAL INFORMATION Gnome Wayland is not affected by this issue.