Performance regression on standalone XR headsets (pico, quest) in 4.3dev2

[DanielKinsman]

Tested versions

Present in:

• 4.3rc1
• 4.3.dev2
• 9b522ac

Not present in:

• 4.3dev1
• 407855b

System information

Godot v4.2.2.stable unknown - Arch Linux #1 SMP PREEMPT_DYNAMIC Wed, 24 Jul 2024 22:25:43 +0000 - Wayland - GLES3 (Compatibility) - AMD Radeon RX 6800 XT (radeonsi, navi21, LLVM 18.1.8, DRM 3.57, 6.10.1-arch1-1) () - AMD Ryzen 7 5800X3D 8-Core Processor (16 Threads)

Issue description

In 4.3dev1 my pico 4 is able to render ~360 sample 3D objects (blender monkey heads) before the framerate drops more than 10fps below the 90Hz refresh rate. In 4.3dev2 that drops to ~300 objects. I tried to bisect it but unfortunately many or even most of the commits in the middle fail to load on the device at all. The best I could narrow it down to was 407855b good, 9b522ac bad.

Steps to reproduce

Use the sample project, run it on the headset. It will start spawning objects until the frame rate drops 10 below the refresh rate at which point it will stop.

Keep your head pointed at same place between runs to make things consistent, I like to look at the monkey on the second from bottom row, that way most of the other monkeys are still rendered in the camera.

Minimal reproduction project (MRP)

https://gitlab.com/DanielKinsman/godot-standalone-xr-perf-test

[decacis]

I found out that the performance drop starts at #84244 (d6caa69)

I used a slightly different MRP, specifically made to reach 72fps on a Quest 2. Simply look forward and have both hands in view, for consistency. The project will start recording results (min, max fps) after a few seconds.

MRP: https://drive.google.com/file/d/1S-zFUpBVAtrE3eP_7M2zRNC_lirOf3X3/view?usp=sharing

I'm using the OpenXR vendors version 2.0.2 in that MRP.

My results:

commit	description	min fps	max fps
9d1cbab	dev1	71	72
d6caa69	#84244	55	61

Note that, in a good portion of the commits that I had to go through when bisecting, I had to cherry-pick #86792 because otherwise, the OpenXR vendors would not load.