https://bugs.kde.org/show_bug.cgi?id=498522
Bug ID: 498522
Summary: kwin_wayland: specific applications cause major
slowdown, mitigated by opening other applications
Classification: Plasma
Product: kwin
Version: 6.2.5
Platform: Fedora RPMs
OS: Linux
Status: REPORTED
Severity: normal
Priority: NOR
Component: performance
Assignee: [email protected]
Reporter: [email protected]
Target Milestone: ---
SUMMARY
kwin_wayland slows from 60 FPS to ~25 FPS when opening 50-100 windows that
overlap (including completely covering each other). I can reproduce this using
any Wayland applications, including Firefox and Konsole, and both on the host
compositor as well as when launching a plain kwin_wayland instance in a nested
window and opening the application windows in there.
The FPS drop happens regardless of the KWIN_DRM_DISABLE_TRIPLE_BUFFERING
setting, and seems to affect just the monitor that the all the windows reside
on: on that monitor dragging any of the windows is very laggy, and the windows
update very slowly (choppy scrolling, bad responsiveness). This is particularly
problematic for Firefox, since its performance is directly tied to the update
rate: loading websites goes from a couple of seconds to over 15 seconds, making
usage quite unbearable. Fullscreening a Firefox window also doesn't help.
Dragging any of the windows to a second monitor (without a lot of windows on
it) restores its performance. Additionally, minimizing all the windows also
fixes the situation, kwin goes back to 60 FPS and responsiveness for all
remaining windows is restored. If switching Firefox to X11 (XWayland), the FPS
drop is greatly reduced (although XWayland is not as smooth in scrolling to
begin with). Interestingly, on the host compositor, opening specific windows,
such as Chromium, kinfocenter or systemsettings, on the affected monitor fixes
all the issues right away. Chromium/kinfocenter/systemsettings stays buttery
smooth, and also increases the FPS of all the other Konsole and Firefox windows
back to 60 FPS. So as long as one of those windows is located on the same
monitor, the performance is as expected, I have no idea why.
STEPS TO REPRODUCE
1. (Optionally) open a nested kwin_wayland instance: `kwin_wayland
--exit-with-session konsole`
2. Make sure Chromium (or any Chromium-based Wayland-enabled thing probably),
kinfocenter and systemsettings aren't running (basically close all other
applications)
2. Open Wayland application windows: `for i in $(seq 100); do { konsole & };
done`
3. Interact with the windows, drag them around, resize them etc.
OBSERVED RESULT
Everything on the affected monitor slows to ~25 FPS, applications are
inresponsive and refresh slowly (especially noticeable when scrolling Firefox).
EXPECTED RESULT
60 FPS, applications stay responsive and smooth. Open
Chromium/kinfocenter/systemsettings on the same monitor to see the desired
result in action.
SOFTWARE/OS VERSIONS
Operating System: Fedora Linux 40
KDE Plasma Version: 6.2.5
KDE Frameworks Version: 6.9.0
Qt Version: 6.7.2
Kernel Version: 6.12.8-cb1.0.fc40.x86_64 (64-bit)
Graphics Platform: Wayland
Processors: 8 × Intel® Core™ i5-8365U CPU @ 1.60GHz
Memory: 31,1 GiB of RAM
Graphics Processor: Mesa Intel® UHD Graphics 620
Manufacturer: LENOVO
System Version: ThinkPad T490
3x identical 1920x1200 60 Hz displays with regular timings, also repro'd on the
laptop's internal display (1920x1080). 100% scaling.
ADDITIONAL INFORMATION
I'm working on providing KWIN_LOG_PERFORMANCE_DATA traces. I also tried to
`perf record` a nested kwin_wayland session, but that doesn't work for some
reason, kwin_wayland just terminates instantly:
$ perf record --call-graph dwarf -- kwin_wayland --exit-with-session konsole
[ perf record: Woken up 1 times to write data ]
[ perf record: Captured and wrote 0,001 MB perf.data ]
Terminated
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