Really slow performance and stability with QT/KDE apps in Manjaro GNOME?

Recently, I've been getting really awful performance that regularly freezes the whole desktop whenever I try to use a major QT/KDE app while logged in to a GNOME session. I assume it must have started at the last update cycle, but I didn't use many QT apps since then so I can't say for sure.

Mostly, it seems to be an issue with the GUI elements; operations that actually require processing power aren't affected much, but if I open a new toolbar, switch a tabbed view, or move or resize the window, then my entire desktop save for the mouse cursor freezes for a couple seconds or more.

If I try to keep using my computer in this state, then the desktop environment will invariably eventually freeze permanently. The clock, system monitor, and other animated features stop moving, and mouse and keyboard input do nothing thereafter. Switching to another tty and killing the offending application or gnome-shell doesn't help, and it stays frozen until I reboot.

After I close a KDE application window without triggering the permanent freeze, all the other open windows will also sometimes become unresponsive to mouse clicks. Everything else still works in this case, in that the shell (and window switcher) will itself still be clickable, all applications still respond to keyboard input properly, and animated windows still continue updating. I can "break out" of this state and re-grab mouse input for my application windows by pressing CTRL+ALT+DELETE to briefly open the GNOME shutdown dialog box in this case, after which everything works normally again.

I've tried the following applications, and they all have this issue:

  • kdevelop

  • okteta

  • krita

Interestingly, kvantummanager, qt5ct, and (qt)designer don't have any problems.

The problem also doesn't occur at all if logged in to a Plasma desktop session, and it's ameliorated in GNOME a little bit if I disable all extensions in the tweak tool.

Additionally, none of my system monitors show any significant RAM, disk, or CPU usage from when the desktop is frozen. strace doesn't seem to show anything going on other than normal mouse movement during a freeze either.

Put together, this leads me to suspect it's caused by an explicit conflict between GNOME and applications that use KDE libraries somewhere over a locking file/socket/pipe/etc, or something like that. But I really have no direct evidence or concrete idea.

Is anyone else having this issue? Is there a known solution for it? And how would one go about diagnosing and repairing it?

I also ran into the same issue while using Okular pdf reader in gnome shell. This almost makes it impossible to use a KDE app in gnome. Not sure anyone has a fix or workaround...

As far as workarounds, I've honestly just installed the entire Plasma shell (without KDE apps) and configured it to look like GNOME for now. It's kinda messy to me in terms of theming and user experience, but not too bad to use for just a couple of programs, and I figure it'd be good to have a fallback desktop to use anyway if I end up breaking GNOME shell later on.

(For your specific case, I'd consider just using Evince instead of Okular, though, unless there are specific features or properties needed from Okular.)

Did your case start happening only recently too?

If so, then it was probably an update that broke it, and we can consider downgrading for now and reporting the issue to the proper channels to get it fixed.

An update that includes most KDE apps and core GNOME/Manjaro packages appears to have been pushed in the last day or so. Installing it seems to have fixed the problem.

There's still a perceptible delay with certain UI elements as compared to in Plasma, for some reason, but I'm pretty sure that was always there.

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