Starting with the premise that "Performance is a Feature", this session will look at how to measure, what to measure and how get the best performance from your .NET code. We will look at real-world examples from the Roslyn code-base and StackOverflow (the product), including how the .NET Garbage Collector needs to be tamed!

1. Performance is a Feature!

2. Why does performance matter?
What do we need to measure?
How we can fix the issues?

3. Front-end
Database & Caching
.NET CLR
Mechanical
Sympathy

4. How?
Measure, measure, measure
1. Identify bottlenecks
2. Know the optimisation works

5. How?
“The simple act of putting a render time in the upper right hand corner of every
page we serve forced us to fix all our performance regressions and omissions.”

6. How?
https://github.com/opserver/Opserver

7. How?
https://github.com/opserver/Opserver

8. How?
The Art of Benchmarking
Profiling -> Micro-benchmarks

9. static void Profile(int iterations, Action action)
{
action(); // warm up
GC.Collect(); // clean up
var watch = new Stopwatch();
watch.Start();
for (int i = 0; i < iterations; i++)
{
action();
}
watch.Stop();
Console.WriteLine("Time Elapsed {0} ms",
watch.ElapsedMilliseconds);
}
http://stackoverflow.com/questions/1047218/benchmarking-small-
code-samples-in-c-can-this-implementation-be-improved

10. private static T Result;
static void Profile<T>(int iterations, Func<T> func)
{
func(); // warm up
GC.Collect(); // clean up
var watch = new Stopwatch();
watch.Start();
for (int i = 0; i < iterations; i++)
{
Result = func();
}
watch.Stop();
Console.WriteLine("Time Elapsed {0} ms",
watch.ElapsedMilliseconds);
}

11. BenchmarkDotNet

12. BenchmarkDotNet Demo

13. How?
Garbage Collection (GC)
Allocations are cheap, but cleaning up isn’t
Difficult to measure the impact of GC
http://www.slideshare.net/benemmett/net-memory-management-ndc-london
https://vimeo.com/113632451

16. Stack Overflow Performance Lessons

18. Stack Overflow Performance Lessons
Use static classes
Don’t be afraid to write your own tools
Dapper, Jil, MiniProfiler,
Intimately know your platform - CLR

20. Roslyn Performance Lessons 1
public class Logger
{
public static void WriteLine(string s) { /*...*/ }
}
public class BoxingExample
{
public void Log(int id, int size)
{
var s = string.Format("{0}:{1}", id, size);
Logger.WriteLine(s);
}
}
Essential Truths Everyone Should Know about Performance in a Large Managed Codebase

21. Roslyn Performance Lessons 1
public class Logger
{
public static void WriteLine(string s) { /*...*/ }
}
public class BoxingExample
{
public void Log(int id, int size)
{
var s = string.Format("{0}:{1}",
id.ToString(), size.ToString());
Logger.WriteLine(s);
}
}
AVOID BOXING

22. Roslyn Performance Lessons 2
class Symbol {
public string Name { get; private set; }
/*...*/
}
class Compiler {
private List<Symbol> symbols;
public Symbol FindMatchingSymbol(string name)
{
return symbols.FirstOrDefault(s => s.Name == name);
}
}

23. Roslyn Performance Lessons 2
class Symbol {
public string Name { get; private set; }
/*...*/
}
class Compiler {
private List<Symbol> symbols;
public Symbol FindMatchingSymbol(string name)
{
foreach (Symbol s in symbols)
{
if (s.Name == name)
return s;
}
return null;
}
}
DON’T USE LINQ

24. Roslyn Performance Lessons 3
public class Example
{
// Constructs a name like "Foo<T1, T2, T3>"
public string GenerateFullTypeName(string name, int arity)
{
StringBuilder sb = new StringBuilder();
sb.Append(name);
if (arity != 0)
{
sb.Append("<");
for (int i = 1; i < arity; i++)
{
sb.Append('T'); sb.Append(i.ToString());
}
sb.Append('T'); sb.Append(arity.ToString());
}
return sb.ToString();
}
}

25. Roslyn Performance Lessons 3
public class Example
{
// Constructs a name like "Foo<T1, T2, T3>"
public string GenerateFullTypeName(string name, int arity)
{
StringBuilder sb = new AcquireBuilder();
sb.Append(name);
if (arity != 0)
{
sb.Append("<");
for (int i = 1; i < arity; i++)
{
sb.Append('T'); sb.Append(i.ToString());
}
sb.Append('T'); sb.Append(arity.ToString());
}
return GetStringAndReleaseBuilder(sb);
}
}
OBJECT POOLING

26. Roslyn Performance Lessons 3
[ThreadStatic]
private static StringBuilder cachedStringBuilder;
private static StringBuilder AcquireBuilder()
{
StringBuilder result = cachedStringBuilder;
if (result == null)
{
return new StringBuilder();
}
result.Clear();
cachedStringBuilder = null;
return result;
}
private static string GetStringAndReleaseBuilder(StringBuilder sb)
{
string result = sb.ToString();
cachedStringBuilder = sb;
return result;
}

27. Roslyn Performance Lessons Demo

28. Resources

29. Questions?
@matthewwarren
www.mattwarren.org