50% performance drop with Activities overlay animations on 4K display (other setups are fine)
Since updating from gnome 3.30 to 3.32, I've noticed a huge regression with performance when it comes to the animations for the gnome-shell Activities overlay. The average FPS of the activities overlay animations seems to cap out pretty reliably around 30 FPS, as opposed to the correct FPS of 60 which the previous release of gnome-shell was able to hit pretty reliably. Interestingly enough, this only seems to be present when I'm using this laptop's main 4K display. If I connect my dock and change the display configuration to 1920x1080+1920x1200+1920x1080, gnome-shell's performance goes back to normal and all shell animations seem to reliably hit 60 FPS.
Based on previous experiences with filing bugs like this, I hopefully should have most of the data you guys need (but of course let me know if I'm missing anything!).
First the actual FPS readings. Note that the following patch was applied to mutter to increase the overall accuracy of the FPS counter:
And the following code was run in the looking glass to slow the animations down, in order to further increase accuracy (since the FPS will usually drop below the actual max if 100% of each frame isn't spent within the animation):
St.set_slow_down_factor(5)
First, the FPS readings with my laptop connected to it's dock with 3x displays (same resolutions as mentioned above):
performance-with-3x-displays.log
Next, output from sysprof for the same scenario:
Next, the FPS readings when only running with my laptop's built-in 4K display enabled:
performance-with-1x-4K-display.log
And finally, output from sysprof for the same scenario:
This has been observed on Fedora 30, using gnome-shell version 3.32.2. I've also tried the following patch and it did not make any noticeable difference: mutter@45244852