It also sounds like fullscreen direct scanout might have worked in jammy but doesn't in noble. You can test that theory by comparing the windowed performance between jammy and noble. Or by checking the scanout method using MUTTER_DEBUG=kms and grepping the log for "Post" (Wayland only though).
** Changed in: gnome-shell (Ubuntu) Status: New => Incomplete -- You received this bug notification because you are a member of Desktop Packages, which is subscribed to gnome-shell in Ubuntu. https://bugs.launchpad.net/bugs/2052913 Title: Large Performance Regression in gnome-shell from Ubuntu Jammy to Ubuntu Noble Status in gnome-shell package in Ubuntu: Incomplete Bug description: Test system: ARM64 Ubuntu Jammy (gnome-shell 42.9-0ubuntu2) and Ubuntu Noble (gnome-shell 45.3-1ubuntu1) Default Ubuntu GNOME desktop environment used with no user added extensions. GPU driverstack identical between the two distros (eliminated as a variable). Linux kernel identical between distros (eliminated as a variable) CPU, GPU, and RAM clocks pinned to max. Test case: Minecraft Java Edition (shared drive with identical setup between Ubuntu versions). Fullscreen 1080p. Xorg display server. FPS (uncapped): Ubuntu Jammy: 177fps Ubuntu Noble: 140fps Observations: Ubuntu Jammy: gnome-shell process cpu% when camera is still: 0-1% gnome-shell process cpu% when camera is moving: 10-20% Memory Bandwidth (CPU and GPU shared): 40% Ubuntu Noble: gnome-shell process cpu% when camera is still: 20-55% gnome-shell process cpu% when camera is moving: 30-55% Memory Bandwidth (CPU and GPU shared): 50% In both cases GPU utilization is observed to be near 100%. So in summary, large performance regression regression which appears to be due to gnome-shell. There is nearly no gnome-shell cpu% usage on ubuntu jammy when there the camera is still (even with a fps graph drawn onscreen) in stark contrast to ubuntu noble. To manage notifications about this bug go to: https://bugs.launchpad.net/ubuntu/+source/gnome-shell/+bug/2052913/+subscriptions -- Mailing list: https://launchpad.net/~desktop-packages Post to : desktop-packages@lists.launchpad.net Unsubscribe : https://launchpad.net/~desktop-packages More help : https://help.launchpad.net/ListHelp