Performance Degradation Moving From alpha 7 to alpha 8+

[lbowers]

Godot version

4.0.alpha8+

System information

Windows 10, Vulcan, AMD Radeon Pro 5700 XT (Driver 20.45.40.15)

Issue description

My project started suffering major performance issues when moving from alpha 7 to alpha 8+. The monitor shows spikes of > 1000ms in the "process" in alpha 8 and alpha 9 - see provided images below. I've been unable to pinpont the code that is causing the issue (see steps to reproduce)

Alpha 7:

Alpha 8+:

Steps to reproduce

I've been unable to identify the cause of the issue, but Remi recommended uploading the project to aid with the locating the problem.

Alpha 7: https://www.youtube.com/watch?v=6q-lwBYfX4A
Alpha 8: https://www.youtube.com/watch?v=f7pWaYF2POQ&t

Minimal reproduction project

bullet-hell-master.zip

Simply hold down the left mouse button when running the above project to reproduce the issue.

[lbowers]

This issue is evident with GLES3 too.

[Lielay9]

I can reproduce the results on my old work laptop (Windows 10 - Nvidia 1050TI).

[Lielay9]

Ok, I think I managed to isolate it. If there's top_level enabled and nodes are freed or added the performance jumps off a cliff. Here's a simple script to reproduce:

extends Node

@export var child_count := 500
@export var enable_top_level := true # Should enable the bug

func _ready() -> void:
	for __ in child_count:
		add_node()

func _process(_delta: float) -> void:
	get_child(0).queue_free()
	add_node()

func add_node() -> void:
	var node := Node2D.new()
	node.top_level = enable_top_level
	add_child(node)

[Calinou]

Is 4.0.alpha8 the release that introduced the HashMap changes? If so, there's a fair chance they are the culprit.

That said, I still recommend bisecting the regression.
If you can compile the engine from source, you could look into bisecting the regression to greatly speed up troubleshooting.

[Lielay9]

@Calinou The results came through and I think you might be somewhat familiar with the culprit... #51591

aabbb4000924182ed5db5128f0e6e32cdc7b851b is the first bad commit
commit aabbb4000924182ed5db5128f0e6e32cdc7b851b
Author: Hugo Locurcio <hugo.locurcio@hugo.pro>
Date:   Thu Aug 12 23:40:13 2021 +0200

    Make `{call,set,notify}_group()` immediate by default

    This results in less surprising behavior out of the box.

    Internal usages were modified to keep the existing behavior
    identical there.

 doc/classes/SceneTree.xml              | 19 ++++++++++++-------
 scene/2d/camera_2d.cpp                 |  6 +++---
 scene/3d/camera_3d.cpp                 |  2 --
 scene/3d/world_environment.cpp         |  4 ++--
 scene/main/scene_tree.cpp              | 24 ++++++++++++------------
 scene/main/scene_tree.h                |  8 +++++---
 scene/main/shader_globals_override.cpp |  2 +-
 scene/main/viewport.cpp                |  2 +-
 scene/resources/material.cpp           |  2 +-
 9 files changed, 37 insertions(+), 32 deletions(-)

Joking aside, it would seem not all internal behavior went through unchanged. A typo perhaps? I'm not quite familiar with these so I'll happily pass the torch.

[Calinou]

Joking aside, it would seem not all internal behavior went through unchanged. A typo perhaps? I'm not quite familiar with these so I'll happily pass the torch.

Apologies, I likely missed some occurrences when performing the search and replace operation across the whole codebase.

[akien-mga]

Should be fixed by #62220.