SUMMARY After random periods of time after session start, KWin decides it's a photo frame and starts producing a slideshow :) It's not a hardware issue (unchanged), not a kernel bug (unchanged), not a Mesa or X server bug (updates reverted), not a lack of resources (CPU, GPU and RAM stats are all fine). Re-login into the session helps but is very annoying. Replacing KWin doesn't help, yet killing and starting it again seems to. Started after an upgrade from 5.18.x to 5.18.90. STEPS TO REPRODUCE 1. I wish I had them, but seems to happen fairly randomly. I had a feeling it sometimes correlates with window resizing or launching chromium-based software, but I'm unsure. Just using the computer for 5-60 minutes is more reliable. OBSERVED RESULT The whole session feels like VNCing over a slow connection EXPECTED RESULT Usable session at all times :) SOFTWARE/OS VERSIONS Operating System: openSUSE Leap 15.1 KDE Plasma Version: 5.18.90 KDE Frameworks Version: 5.70.0 Qt Version: 5.15.0 Kernel Version: 5.7.0-3.gad96a07-default OS Type: 64 bits Processors: 8 × Intel® Core™ i5-10210U CPU @ 1.60GHz Memory: 15,3 Gb RAM Graphics Processor: Mesa DRI Intel® HD Graphics ADDITIONAL INFORMATION When the problem occurs, there appears to be a consistent slow paint interval. It seems to not affect window decorations and effects sometimes, and it doesn't affect the mouse cursor, but it always affects window contents. If all windows are closed, Plasma behaves smoothly, too.
Replacing KWin seems to also help now; didn't help earlier, maybe is somehow related to x11 downgrade. Anyway, I have found one way to consistently reproduce this on my machine: restore and then maximize Firefox with CSD enabled by dragging its headerbar to the top edge.
The key seems to be in the maximize animation itself, when kwin animates the future region for the app. Just reproduced with Telegram as well.
> affect the mouse cursor, but it always affects window contents. Urgh, it could be that I broke it.... :/ Do you see some other unusual things, e.g. high CPU usage, etc?
> Do you see some other unusual things, e.g. high CPU usage, etc? No, as I mentioned, all observable resources are fine... But I managed to find the reason: the issue was somehow caused by a popular KWin script called Parachute (https://github.com/tcorreabr/Parachute). Disabling it fixes the problem for me, and re-enabling returns it. I don't know though if it's a bug in the script or in KWin itself.
I'd start with Parachute. IIRC the developers is aware that it's implemented in an inefficient way right now. He might be open to assistance on that front. See https://phabricator.kde.org/T13224
I suspect there's some KWin bug still involved here since the issue occurs when the effect shouldn't even be triggered and persists for the whole session afterward. But I don't know enough of what KWin scripting API allows to do to be sure.