Sometimes, seemingly randomly, repainting of one window stalls. Firefox is common, but it has happened to some other windows as well, like some KF5-based application (cannot remember which one(s)). Switching to another window and then back using Alt+Tab causes the stalled window to be repainted once or twice, but it will then remain stalled. Disabling compositing fixes the stall and makes the window repaint again. Then after enabling compositing again the window is still being repainted. I haven't witnessed the window to start being repainted again without disabling compositing. I haven't found a pattern that causes this stall to occur. I think I haven't been writing any text when this has happened, but I might have been pressing some shortcuts. I'm also using fcitx as input method. Attached KWin support information and output of nvidia-smi were taken a bit after Firefox's window started stalling and when it was still stalling. It wasn't taken in a VT because all other windows were repainting fine and still are while writing this. Reproducible: Sometimes
Created attachment 90473 [details] Output of nvidia-smi
Created attachment 90474 [details] KWin support information
Since firefox (surprise...) seems a reliable trigger, could you try to "about:config" and filter for a) webgl -> set "webgl.disabled" to true and pdfjs.enableWebGL to false (latter is the default) b) accel -> set "layers.acceleration.disabled" to true Restart firefox and see whether this still happens.
Ok, done. Let's see whether this still happens.
Repainting of Firefox's window stalled again in the same way.
"kcmshell5 kwincompositing" -> does it also happen w/ xrender compositing?
Also happens with XRender compositing.
This hasn't happened in a really long time now.
Thanks for the update, may have been https://git.reviewboard.kde.org/r/124591/