https://bugs.kde.org/show_bug.cgi?id=501524
Bug ID: 501524
Summary: Excessive bell usage leads to sluggishness
Classification: Plasma
Product: kwin
Version: 6.3.3
Platform: NixOS
OS: Linux
Status: REPORTED
Severity: normal
Priority: NOR
Component: xwayland
Assignee: kwin-bugs-n...@kde.org
Reporter: alo...@gmx-topmail.de
Target Milestone: ---
SUMMARY
X11 applications (through XWayland) using the bell excessively will cause KWin
to become very sluggish to react to user events. In the worst cases this can
lead to feedback loops making the session unusable.
STEPS TO REPRODUCE
1. Open some xterms (2 or 3 seems to be enough to reproduce the issue without
causing too much instability)
2. Run `while true; do sleep 0.01; echo -e '\a'; done` in each of them
OBSERVED RESULT
The system becomes sluggish to react to user events (keyboard input, cursor
movement).
EXPECTED RESULT
The system continues operating normally.
SOFTWARE/OS VERSIONS
Windows:
macOS:
(available in the Info Center app, or by running `kinfo` in a terminal window)
Linux/KDE Plasma: 6.14.0-rc6
KDE Plasma Version: 6.3.3
KDE Frameworks Version: 6.11.0
Qt Version: 6.8.2
ADDITIONAL INFORMATION
* When the bug is triggered, CPU usage is high in kwin_wayland and wireplumber
processes, and the degradation becomes more noticeable once wireplumber gets
close to a full core of CPU usage. However simply playing back the bell sound
in a `pw-play` loop, even using many parallel processes, does not reproduce the
bug. This suggests that the issue may actually be KWin blocking on the sound
system when the bell is triggered.
* Originally the issue was observed in GeoGebra, which rings the bell when
backspace is hit in the empty input field. Holding the backspace key for some
seconds will be enough to trigger the issue, seemingly resulting in key repeat
becoming stuck, further exacerbating the issue to the extent that the session
will be fully unusable.
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