GNOME 40 performance regression: when activating Overview mode, GNOME Shell eats the CPU and fps drops to ~0.1 fps, lagging input
I have a Dell Inspiron 530n desktop computer with Intel G31/G33 graphics (or is it GMA 3000, 3100, etc.? I have no idea, doesn't seem to be an easy way for me to be sure; lsPCI says g31 while GNOME Control Center says G33). It's a reasonably capable computer (I've been using it for years as my workstation) and until now, it had no problems running GNOME Shell... until GNOME 40 / Fedora 34.
With that version, whenever the Overview is shown, the CPU usage goes to 100% (one of the cores is pegged), animations slow to a crawl (I have no way to measure this, but it really feels like 0.1-0.5 frames per second), and the system becomes unresponsive to mouse movements/clicks and keyboard input, until you exit the overview, which can easily take 20-30 seconds because the system is so unresponsive; the only way I have to exit this CPU death loop when I accidentally trigger the Super/Win key, is to mash (or press and hold) the Escape key.
This of course is also problematic considering that recent versions of GNOME open the Overview by default on login. You basically have to mash the Esc button on the keyboard as soon as you log in, and then use Alt+F2 to launch anything afterwards...
I monitored journalctl -f
via SSH while this was happening, and nothing gets printed to the logs when this happens, unfortunately.
This happens both on a Fedora 34 liveUSB, or an installed Fedora 33 on that machine that then was fully upgraded to Fedora 34, whether running the Wayland GNOME session or the Xorg GNOME session. When not in overview mode, graphics in GNOME Shell with that hardware are butter-smooth, so the hardware certainly still is capable of doing the job here.
Fedora 33 / GNOME 3.38 did not exhibit the problem.
It seems someone else previously encountered the same issue I've encountered today, with the same computer, (the "n" in 530n simply meant it was the model that came preloaded with Linux by Dell): https://ask.fedoraproject.org/t/cant-install-fedora-34-gnome-anaconda-black/14374 ...but I'm taking the time to report it upstream here because I can easily reproduce it on one of my computers. I just don't know how to troubleshoot it properly, so please advise which information I should provide and how to collect it.