When you profile your application, there are some common issues that you might come across. This page outlines how to investigate the cause of some common performance issues.
When looking at a trace of start-up times, there are two key methods to inspect:
UnityLoadApplication. These two methods are the primary places where the configuration, assets, and code of a project can impact start-up time.
Note: The start-up time of your application differs from platform to platform. On most platforms, start up happens while the splash screen appears.
In the above screenshot from an Instruments trace of an example Unity project running on an iOS device, in the platform-specific
startUnity method, note the
UnityInitApplicationGraphics performs a lot of internal work, such as setting up the graphics device and initializing a lot of Unity’s internal systems. It also initializes the Resources system by loading an index of all the files contained in the Resources system.
Unity’s Resource system includes every asset file in its data that’s in the
Resources folder in the
Assets folder of your project. This includes any files in the
Resources folder’s children folders. As such, the time required to initialize the Resources system increases in correlation with the number of files within the
Resources folders in your application’s project.
UnityLoadApplication contains methods that load and initialize the first SceneA Scene contains the environments and menus of your game. Think of each unique Scene file as a unique level. In each Scene, you place your environments, obstacles, and decorations, essentially designing and building your game in pieces. More info
See in Glossary in the project. This includes deserializing and instantiating the data necessary to display the first Scene, such as compiling ShadersA program that runs on the GPU. More info
See in Glossary, uploading Textures and instantiating GameObjectsThe fundamental object in Unity scenes, which can represent characters, props, scenery, cameras, waypoints, and more. A GameObject’s functionality is defined by the Components attached to it. More info
See in Glossary. Also, Unity executes the
Awake callbacks of all
MonoBehaviours in the first Scene.
These processes mean that if there is any long-running code in an
Awake callback in the first Scene of a project, that code could be responsible for slowing down the project’s initial start-up time. Resolving this involves either eliminating the slow code, or executing it elsewhere in the application’s lifecycle.
For profiling traces captured after the initial startup time, the primary place of interest is the method
PlayerLoop. This is Unity’s main loop, and the code within it runs once per frame.
The above screenshot illustrates several of the most performance-impacting methods within
PlayerLoop. Note: The names of methods within the
PlayerLoop might vary between Unity versions.
PlayerRender is the method that runs Unity’s rendering system. This includes culling objects, calculating dynamic batches, and submitting drawing instructions to the GPU. Any Image Effects or rendering-based script callbacks (OnWillRenderObject, for example) also run here. In general, this should be the top consumer of CPU time while the project is interactive.
BaseBehaviourManager calls three templated versions of
CommonUpdate. These invoke certain callbacks within the
MonoBehaviours attached to active GameObjects in the current Scene:
FixedUpdateif the physics system has ticked
BaseBehaviourManager::CommonUpdate<UpdateManager> is the most useful method family to inspect, because it’s the entry point for most of the script code running within a Unity project.
There are several other methods that are useful to inspect:
UI::CanvasManagerinvokes several different callbacks if a project uses the UGUI system. This includes Unity UI(User Interface) Allows a user to interact with your application. Unity currently supports three UI systems. More info
CanvasManagerto appear in the ProfilerA window that helps you to optimize your game. It shows how much time is spent in the various areas of your game. For example, it can report the percentage of time spent rendering, animating, or in your game logic. More info
PhysicsManager::FixedUpdateruns the PhysX physics system. This primarily involves running PhysX’s internal code. The number of physics objects in the current Scene, such as
Colliderinfluence PhysX’s internal code. Physics-based callbacks also appear here: in particular,
If the project is using 2D physics, that appears as a similar set of calls under
When scriptsA piece of code that allows you to create your own Components, trigger game events, modify Component properties over time and respond to user input in any way you like. More info
See in Glossary are invoked on platforms cross-compiled with IL2CPPA Unity-developed scripting back-end which you can use as an alternative to Mono when building projects for some platforms. More info
See in Glossary, look for trace lines that contain a
ScriptingInvocation object. This is the point where Unity’s internal native code transitions into the script runtime to execute script code. Note: Technically, after Unity runs your C# code through IL2CPP, it also becomes native code. However, this cross-compiled code primarily executes methods via the IL2CPP runtime framework and doesn’t resemble handwritten C++.
In the above screenshot, the methods nested beneath the
RuntimeInvoker_Void line are part of cross-compiled C# scripts that Unity executed once per frame.
The trace lines’ names are the name of the original class followed by an underscore and the name of the original method. In this example trace, you can see
PlayerShooting.Update and several other
Update methods. These are the standard Unity
Update callbacks found in most
You can expand these methods to see which methods within them consumed CPU time. This includes other script methods within the project, Unity APIs, and C# library code.
The above trace shows that the
StandaloneInputModule.Process method was ray casting through the entire UI once per frame. This method detects whether any touch events were hovering over, or activating any UI elements. The method iterating over all the UI elements, and testing whether the mouse’s position is within their bounding rectangle is resource-intensive.
You can also identify asset loading in CPU traces. The main method that indicates an Asset load is
SerializedFile::ReadObject. This method connects a binary data stream from a file to Unity’s serialization system, which operates via a method named
Transfer method is on all Asset types, such as Textures, MonoBehaviours and Particle SystemsA component that simulates fluid entities such as liquids, clouds and flames by generating and animating large numbers of small 2D images in the scene. More info
See in Glossary.
The above screenshot is a trace of Unity loading a Scene. When it loads a Scene, Unity reads and deserializes all the Assets within the Scene, as denoted by the calls to various
Transfer methods beneath
If you see a performance stutter during runtime and the performance trace shows that
SerializedFile::ReadObject used a significant amount of time, it means that Asset loads reduced the frame rate. Note:
SerializedFile::ReadObject usually appears on the main thread when the
Resources or AssetBundle APIs request synchronous Asset loads.
To resolve this performance stutter can you can make Asset loading asynchronous (which moves the heavy
ReadObject call to a worker thread), or preload certain heavy Assets.
Transfer calls also appear when Unity clones objects (denoted by the
CloneObject method in a trace). If a call to
Transfer appears beneath a
CloneObject call, then Unity isn’t loading the Asset from storage. Instead, Unity transfers the old object’s data to the new object. To do this, Unity serializes the old object and deserializes the resulting data as the new object.