Analyzing Profiler traces

Export and analyze detailed Profiler trace data to identify optimization opportunities.

Read time 6 minutes

Last updated 13 days ago

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.

Dissecting startup traces

When looking at a trace of start-up times, there are two key methods to inspect:

UnityInitApplicationGraphics

and

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

and

UnityLoadApplication

methods.

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 Scene in the project. This includes deserializing and instantiating the data necessary to display the first Scene, such as compiling Shaders, uploading Textures and instantiating GameObjects. Also, Unity executes the

Awake

callbacks of all

MonoBehaviour

s 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.

Dissecting runtime traces

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.

Instruments trace of an example Unity project

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

MonoBehaviour

s attached to active GameObjects in the current Scene:

```
CommonUpdate<UpdateManager>
```
calls
```
Update
```
callbacks

CommonUpdate<LateUpdateManager>

calls

LateUpdate

callbacks

CommonUpdate<FixedUpdateManager>

calls

FixedUpdate

if the physics system has ticked

In general,

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::CanvasManager
```
invokes several different callbacks if a project uses the UGUI system. This includes Unity UI’s batch computation and layout updates; the two operations that most often cause
```
CanvasManager
```
to appear in the Profiler.
```
DelayedCallManager::Update
```
runs coroutines.
```
PhysicsManager::FixedUpdate
```
runs the PhysX physics system. This primarily involves running PhysX’s internal code. The number of physics objects in the current Scene, such as
```
Rigidbody
```
and
```
Collider
```
influence PhysX's internal code. Physics-based callbacks also appear here: in particular,
```
OnTriggerStay
```
and
```
OnCollisionStay
```
.

If the project is using 2D physics, that appears as a similar set of calls under

Physics2DManager::FixedUpdate

Dissecting a script method

When scripts are invoked on platforms cross-compiled with IL2CPP, 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

EventSystem.Update

PlayerShooting.Update

and several other

Update

methods. These are the standard Unity

Update

callbacks found in most

MonoBehaviours

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.

Asset loading

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

. The

Transfer

method is on all Asset types, such as Textures, MonoBehaviours and Particle Systems.

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

SerializedFile::ReadObject

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

SceneManager

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.

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