https://bugs.kde.org/show_bug.cgi?id=478915
Bug ID: 478915
Summary: Continuous CPU load after X11 login
Classification: Plasma
Product: kwin
Version: 5.91.0
Platform: Other
OS: Linux
Status: REPORTED
Severity: normal
Priority: NOR
Component: general
Assignee: kwin-bugs-n...@kde.org
Reporter: jpe...@petsovits.com
Target Milestone: ---
Created attachment 164388
--> https://bugs.kde.org/attachment.cgi?id=164388&action=edit
Flamegraph SVG of kwin_x11 at a constant but not debilitating load
SUMMARY
Logged into my Plasma 6.0 Beta dev session (built two days after Beta 2) and
the fans started spinning. On an 8-core Intel Core i7-8565U, ThinkPad X1 Carbon
Gen 7 laptop with iGPU, ksysguard showed a constant 13%-14% of CPU usage for
kwin_x11 and 4%-5% for picom. So it didn't quite incapacitate the system, and
cursor overlays were fluid but window moves were at an estimated <5 FPS.
I don't have a full stacktrace, but I used
https://github.com/flamegraph-rs/flamegraph to capture a few seconds of
constant load and generate a flamegraph SVG. Find the SVG attached. It looks
like debuginfod was not used because the system-level libraries don't show
function-level info. Sorry. I figure the actual perf.data output is also not
useful outside of my system, but I have it sitting here for a few days until I
rebuild kwin again sometime.
STEPS TO REPRODUCE
1. Log into a KF6 X11 session.
2. Get lucky, notice high system load.
3. ???
4. `perf` it!
SOFTWARE/OS VERSIONS
Operating System: Arch Linux
KDE Plasma Version: 5.91.90
KDE Frameworks Version: 5.248.0
Qt Version: 6.6.1
Kernel Version: 6.6.3-arch1-1 (64-bit)
Graphics Platform: X11
Processors: 8 × Intel® Core™ i7-8565U CPU @ 1.80GHz
Memory: 15.3 GiB of RAM
Graphics Processor: Mesa Intel® UHD Graphics 620
Manufacturer: LENOVO
Product Name: 20QD001VUS
System Version: ThinkPad X1 Carbon 7th
ADDITIONAL INFORMATION
* The session I had previously logged into was a Plasma 5.27.9 session on X11.
(Picked the wrong X11 SDDM entry because usually this user account is reserved
for Plasma 6 only.)
* Upon logout from the CPU-intensive KF6 X11 session, SDDM did not come back
and the screen stayed black. Probably unrelated as it also happened after the
next session.
* Following a hard reboot, I logged into the same KF6/X11 Plasma session again
to see if the issue is always reproducible. It is not, CPU load was nice and
low now.
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