Godot 4 fps performance regression

[godtmilk]

Godot version

4.0, 4.0.3, 4.1

System information

linux-ubuntu20-xorg / windows 10 gtx 1070

Issue description

If the same scene is used in Godot 3 and 4, then there is an undesirable disparity in performance with Godot 4 producing less fps.

Example 1.

A scene with multimesh and many instanced grass:

engine: godot 3.5
renderer: gles3
display window: 1024 x 600
grass triangles: 600,000
fps: ~600

engine: godot 4.1
renderer: forward+
display window: 1024 x 600
grass triangles: 600,000
fps: ~330

engine: godot 4.1
renderer: mobile
display window: 1024 x 600
grass triangles: 600,000
fps: ~570

engine: godot 4.1
renderer: compatibility
display window: 1024 x 600
grass triangles: 600,000
fps: ~570

Also, in linux there is a huge difference between the fps when using an empty scene.

Example 2.

An empty scene in linux:

engine: godot 3.5
renderer: gles3
display window: 1024 x 600
fps: ~5000

engine: godot 4.1
renderer: forward+
display window: 1024 x 600
fps: ~1500

engine: godot 4.1
renderer: mobile
display window: 1024 x 600
fps: ~1500

engine: godot 4.1
renderer: compatibiltiy
display window: 1024 x 600
fps: ~3200

• An empty scene in windows 10 did not have a big difference between the fps, both
  3.5.2(gles3) and 4.1(forward+) having around 2500 fps.

Steps to reproduce

Use the included projects or compare between godot 3 and 4 with your own scene.

Minimal reproduction project

Grass_Scene.zip

[Calinou]

Consolidating in #68959. Thanks for the report!

Also, in linux there is a huge difference between the fps when using an empty scene.

On NVIDIA + Linux, fullscreen performance in Vulkan apps seems to be much lower in a maximized window compared to fullscreen. I noticed this when running vkcube or https://github.com/Calinou/vulkan-tutorial in a maximized window versus actual fullscreen. As this is not exclusive to Godot, this isn't something we can fix.