SUMMARY I am not sure if this is a bug in KWin, or Plasma etc - please reassign the product if I made a mistake. Dragging icons and other objects with a mouse causes a lot of stutter and high CPU usage in Xorg process. I think it started happening in Plasma 6.1.0. STEPS TO REPRODUCE 1. Click and drag an icon from a task bar; it also happens when you drag e.g a clickable link in a browser. 2. Similar, although slightly less visible effect is when moving the mouse cursor over the task manager icons, mouse cursor kind of slows down and starts to stutter, when it is outside the toolbar it moves smoothly again. It also causes 98% CPU usage. OBSERVED RESULT Xorg process CPU usage jumps to 98%, there is a visible system slowdown, dragged icon or link moves with a visible stutter. EXPECTED RESULT There is no CPU usage hike, dragged object and cursor moves smoothly. SOFTWARE/OS VERSIONS Linux/KDE Plasma: Fedora 40 KDE Plasma Version: 6.1.3 KDE Frameworks Version: 6.4.0 Qt Version: 6.7.2 NVidia Driver: 550.67 ADDITIONAL INFORMATION See attached video: https://photos.app.goo.gl/SGV5jbhbi5fdRgva8
One more important detail: right after a reboot or clean login, the issue is gone. I resumed the system from sleep after the night and it stutters, but then I logged out and logged back in, and it was smooth again. I also tested the latest NVIDIA driver, but it made no difference.
I found the root cause - it is the Jetbrains Toolbox application (!!!). As soon as I start it, the stutter starts. When I quit it, it system behaves normally.
I have reported the problem in the Jetbrains Toolbox project: https://youtrack.jetbrains.com/issue/TBX-12499/Starting-Jetbrains-Toolbox-causes-major-UI-slowdowns