Game Programming 13 - Debugging & Performance Optimization

Game Programming
Debugging & Performance Optimization
Nick Prühs

Objectives
• To get an overview of techniques for preventing bugs beforehand
• To learn how to track down and properly remove bugs from your
code
• To understand possible performance bottlenecks
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Why you should always start debugging immediately
• Code entropy says your code will get worse, all the time, unless you
actively invest in preventing that
• Broken windows theory says the worse your code is, the worse it will
become
• Tracking down bugs is harder in a larger code base
• Tracking down bugs is harder in a buggy code base
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Code Quality Tools
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/// <summary>
/// Attaches the passed component to the entity with the specified id.
/// Note that this manager does not check whether the specified id is valid.
/// </summary>
/// <exception cref="ArgumentNullException">
/// Passed component is null.
/// </exception>
/// <exception cref="InvalidOperationException">
/// There is already a component of the same type attached.
/// </exception>
public void AddComponent(int entityId, IEntityComponent component)
{
if (component == null)
{
throw new ArgumentNullException("component");
}
if (this.components.ContainsKey(entityId))
{
throw new InvalidOperationException(
"There is already a component of type " + component.GetType() + " attached to entity with id "
+ entityId + ".");
}
this.components.Add(entityId, component);
this.OnComponentAdded(entityId, component);
}

You need a repro. Period.
How can you be sure you’ve fixed it?
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Stack Traces
Object reference not set to an instance of an object
at LifeApplication.Initializer.CreateManagers () [0x00488] in
Initializer.cs:481
at LifeApplication.Initializer.OnLoad () [0x00016] in
Initializer.cs:235
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What’s null here?
// Initialize progress manager.
var progressConfig = new ProgressConfig(this.unityLoader.Version.Code);
if (this.config.Progress.Encrypt)
{
progressConfig.SetEncryption(
this.config.Progress.Encryption.EncryptKey,
this.config.Progress.Encryption.EncryptIv);
}
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What’s null here?
{
}
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What’s null here?
{
}
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What’s null here?
{
}
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What’s null here?
{
}
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What’s null here?
{
}
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Conditional Breakpoints
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Crash Dump Analaysis
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C:Program FilesProcdump>procdump.exe -ma -i D:TempDumps
ProcDump v7.0 - Writes process dump files
Copyright (C) 2009-2014 Mark Russinovich
Sysinternals - www.sysinternals.com
With contributions from Andrew Richards
Set to:
HKLMSOFTWAREMicrosoftWindows NTCurrentVersionAeDebug
(REG_SZ) Auto = 1
(REG_SZ) Debugger = "C:Program FilesProcdumpprocdump.exe" -accepteula -ma
-j "D:TempDumps" %ld %ld %p
Set to:
HKLMSOFTWAREWow6432NodeMicrosoftWindows NTCurrentVersionAeDebug
(REG_SZ) Auto = 1
(REG_SZ) Debugger = "C:Program FilesProcdumpprocdump.exe" -accepteula -ma
-j "D:TempDumps" %ld %ld %p
ProcDump is now set as the Just-in-time (AeDebug) debugger.

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C:Program FilesProcdump>procdump.exe -u
ProcDump v7.0 - Writes process dump files
Copyright (C) 2009-2014 Mark Russinovich
Sysinternals - www.sysinternals.com
With contributions from Andrew Richards
Reset to:
HKLMSOFTWAREMicrosoftWindows NTCurrentVersionAeDebug
(REG_SZ) Auto = <deleted>
(REG_SZ) Debugger = "C:WINDOWSsystem32vsjitdebugger.exe" -p %ld -e %ld
Reset to:
HKLMSOFTWAREWow6432NodeMicrosoftWindows NTCurrentVersionAeDebug
(REG_SZ) Auto = <deleted>
(REG_SZ) Debugger = "C:WINDOWSsystem32vsjitdebugger.exe" -p %ld -e %ld
ProcDump is no longer the Just-in-time (AeDebug) debugger.

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Deferencing a nullptr that will cause a crash

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Minidump File Summary in Visual Studio

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Debugging a Minidump in Visual Studio

Pair Programming
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Source: University of Utah, UIT

And if nothings helps …
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And if nothings helps …
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TRY AGAIN
TOMORROW!

Some are really nasty …
• Remote systems
• Race conditions
• Mobile development, embedded systems, drivers
• “Release Mode only” bugs
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Quoting My Tutor
“If the bug is not where you expect it to be,
you better start looking for it where you’re not expecting it to be.”
- Hagen Peters
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Why you should never start optimizing immediately
• Your code base will change over time, a lot, most likely removing
some of the code you’ve spent time on optimizing
• Optimized code tends to be hard to read
▪ … and thus, hard to debug.
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Performance Optimization
1. Profile first!
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1. Profile first!
2. Profile again!
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1. Profile first!
2. Profile again!
3. Identify the bottlenecks: GPU vs. CPU vs. Memory
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Fighting CPU Bottlenecks
Pooling
Trades memory for CPU performance.
Re-uses objects to prevent costly construction and destruction.
Requires proper (cheap) reset of pooled objects.
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Caching
Trades memory for CPU performance.
Stores computed values for later use.
Requires proper cache invalidation whenever the input changes.
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Bucketing
Trades accuracy for CPU performance.
Distributes computations across multiple frames by dividing operation
into multiple input sets.
Can only be applied if player doesn’t notice difference immediately (e.g.
updating AI just twice per second).
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Gotcha!
Always turn off logging before
profiling!
Otherwise, disk I/O will lead to
false results.
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Hint
If no native profiling tools are
available (or applicable), you can
always fall back to utility classes
such as
System.Diagnostics.Stopwatch.
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Memory Leaks
• allocated memory that is never released
▪ in most cases, the reference or pointer is not even available any
more
▪ if occurring on a regular basis (e.g. every time a level is loaded),
will eventually fill up all available memory and crash the game
• in Ansi C: “no malloc without free”
• in C++: “no new without delete”
▪ in modern C++, usually achieved by the means of smart pointers

Gotcha!
Managed runtime
environments can leak
memory, too!
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Memory Leaks
• make sure to always remove all registered event handlers in
languages like C#
• more complicated runtime environments can represent unique
challenges
▪ e.g. Mono heap in Unity
• it might be a good idea to return to an “empty scene” once in a while
and verify all memory has been properly cleaned up

References
• McShaffry. Debugging Your Game … or “That’s not supposed to
happen!”. Austin Game Conference, 2003.
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Thank you!
http://www.npruehs.de
https://github.com/npruehs
@npruehs
nick.pruehs@daedalic.com

5 Minute Review Session
• Why should you always start debugging immediately?
• Why should you never start optimizing immediately?
• Name a few tools and approaches for tracking down broken code!
• How do you know whether you’ve got an GPU, CPU or memory
bottleneck?
• Name a few techniques for fighting CPU bottlenecks!

Game Programming 13 - Debugging & Performance Optimization

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Game Programming 13 - Debugging & Performance Optimization