I've installed KDE neon 5.21 and have run for the second time in 2 days into this crippling issue. Unfortunately, reproducibility is occasional.
STEPS TO REPRODUCE
1. Go to System Settings -> Window Management -> Window Behavior
2. Check "Active screen follows mouse"
The OS becomes almost unresponsive. The mouse cursor is responsive, but key presses are buffered and echoed slowly, and switching windows is extremely slow. However, System Monitor reports low CPU usage (under 5%) and is itself the application taking up the most CPU. RAM utilization was under 50% of the 16GB.
The other time I've seen the same behavior was when I switched the Task Switcher to Thumbnails Grid.
KDE Frameworks Version: 5.79.0
Qt Version: 5.15.2
Mesa Intel UHD Graphics 620 on a Core i7 ThinkPad X1C 7th gen connected to external monitor via USB-C
Logging out and back in did not fix the slowness. I had to reboot.
Please let me know what additional debugging information I can provide when this will happen a 3rd time. Unfortunately I need a stable system so I'll have to revert to a stable version of Plasma after that, unless the bug gets fixed.
Created attachment 135871 [details]
some jourrnalctl logs
I don't think it's necessarily related to that. I've got 100% reproducibility with
1. Open lutris
2. Open Origin
If i click on play in lutris and don't move the mouse the screen with stay on "Connecting to Origin" window. As soon as I move the mouse it starts loading the launcher, but the desktop is very sluggish.
I also noticed that dmesg will print:
perf interrupt took too long
Do you have any of these errors?
Created attachment 135873 [details]
dmesg -T output
I do see "perf: interrupt took too long" in the `dmesg` output, but *after* I rebooted post-crawl. I've attached the `dmesg -T` output up to the timestamp at which I submitted this bug, which was after I rebooted.
Issue has just happened again after changing a few font sizes.
At this point I'm highly reluctant to change any System Settings, due to the high likelihood of having to reboot.
Please let me know if there's a workaround, otherwise I'll have to revert to Plasma 5.18.
"perf: interrupt took too long" is a message that comes from the kernel. Some web searching found a few other examples of people experiencing this same issue in non-Plasma contexts. Seems like your kernel is not happy about something. I think you'll want to submit a bug report at https://bugzilla.kernel.org/. Thanks!
"perf: interrupt took too long" did *not* appear in the `dmesg` output before the ~freeze; only hours after. And the freeze has been triggered only by actions in System Settings that affected the display.
The kernel should be the same as in Kubuntu (where I had not exeprienced this issue on) because I'm running KDE neon 5.21, which claims to be based on the stable Ubuntu 20.04.2 LTS. Its version is 5.4.0-65-generic.
Hmm, maybe that's not related, then.
Happened again when I pressed Alt+F3 to have a window remember its size and position.
Happened again with 5.21.2 when I toggled off the Task Switcher option to Show selected window
Happened again when adding properties to the Special Application settings (tried to make VokoscreenNG remember its size and position, but that just doesn't work - https://github.com/vkohaupt/vokoscreenNG/issues/156)
This bug is fdriving me insane. Now I've created a new Virtual Desktop, and the entire OS slowed to a crawl. Have to reboot again.
Does restarting kwin_x11 fix it?
Whilst it is slow, please run:
perf record --call-graph dwarf -p `pidof kwin_x11`
Created attachment 141162 [details]
I've run `kwin_x11 --replace` to clear up the ghost window left by #438552. That brought the system to the ridiculous slowness I've described.
I've run that perf command and attached the data file.
Happened again after adding a new virtual desktop. After I clicked Apply - 💥
Running `kwin_x11 --replace` didn't help. Will have to reboot.
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.