SUMMARY When a notification pops up, kwin_x11 uses up to 90% of the CPU for a few seconds. STEPS TO REPRODUCE 1. Enter command "notify-send anything" in Konsole OBSERVED RESULT Notification pops up. Whole system lags for a second or two, and kwin spikes to around 90% CPU usage in that time. EXPECTED RESULT A notification without the lag. SOFTWARE/OS VERSIONS Operating System: KDE neon 5.18 KDE Plasma Version: 5.18.3 KDE Frameworks Version: 5.68.0 Qt Version: 5.14.1 Kernel Version: 5.3.0-42-generic OS Type: 64-bit Processors: 16 × AMD Ryzen 7 2700X Eight-Core Processor Memory: 15.6 GiB of RAM Nvidia Proprietary driver version 435.21 GTX 1070 ADDITIONAL INFORMATION Especially annoying when playing a game, because in-game the fps drops down to like 5-10fps during the high cpu usage. Telegram and Discord notifications are no exception. Switching to XRender backend seems to nearly eliminate the lag, but it's still noticeable for less than a second, and there seems to be no usage spike. OpenGL 2.0 makes kwin_x11 spike to around 70% OpenGL 3.1 makes kwin_x11 spike to around 90%
Can't reproduce this bug with AMD.
Disabling "Force (Full) Composition Pipeline" in NVIDIA settings and exporting KWIN_TRIPLE_BUFFER=1 seems to lower the usage spike significantly. OpenGL 3.1: ~10% OpenGL 2.0: ~10% XRender: <2% (These are measured in KSysGuard, Process Table, "CPU %" without dividing by number of CPUs) Unfortunately the lag is still there with OpenGL, although less severe. Using XRender makes it nearly unnoticeable.
Okay the lag is still there, I guess it was a placebo. I enabled do not disturb forever, now it doesn't lag but I can't see incoming notifications :/
This bug was reported against an outdated version of KWin. We have made many changes since the. If the issue persists in newer versions can you reopen the bug report updating the version number.