A brief discussion of performance optimization and when to do it, of how to benchmark and use BenchmarkDotNet, and some common gotchas in the .NET framework that you may or may not be aware of. Presented at NDC London, 30 Jan 2019 Code used to generate benchmarks: https://github.com/davidwengier/Benchmark

1. NDC { London }
2019
David Wengier
Microsoft
@davidwengier

2. @davidwengier

3. - Donald Knuth
@davidwengier

4. - Donald Knuth
@davidwengier

5. We should forget about small efficiencies, say about
97% of the time: premature optimization is the root
of all evil. Yet we should not pass up our opportunities
in that critical 3%
- Donald Knuth
@davidwengier

6. We should forget about small efficiencies, say about
97% of the time: premature optimization is the root
of all evil. Yet we should not pass up our opportunities
in that critical 3%”
- Donald Knuth
“Structured Programming with Go To Statements”, 1974@davidwengier

7. @davidwengier

8. @davidwengier

9. @davidwengier

10. “Don’t do that, that’s slow, and uses too much memory!”
@davidwengier

11. public static void Profile(Action func)
{
DateTime start = DateTime.Now;
for (int i = 0; i < 100; i++)
{
func();
}
Console.WriteLine(“Avg Time Elapsed {0} ms", (DateTime.Now - start).TotalMilliseconds / 100);
}

12. public static void Profile(Action func)
{
Process.GetCurrentProcess().PriorityClass = ProcessPriorityClass.High;
Thread.CurrentThread.Priority = ThreadPriority.Highest;
func();
Stopwatch watch = new Stopwatch();
GC.Collect();
GC.WaitForPendingFinalizers();
GC.Collect();
watch.Start();
for (int i = 0; i < 100; i++)
{
func();
}
watch.Stop();
Console.WriteLine(“Avg Time Elapsed {0} ms", watch.Elapsed.TotalMilliseconds / 100);
}

13. https://benchmarkdotnet.org/
https://github.com/dotnet/BenchmarkDotNet
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21. 0 bytes allocated 32 bytes allocated

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24. 0 bytes 20 bytes 32 bytes

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@davidwengier

29. public class HybridDictionary: IDictionary {
// These numbers have been carefully tested to be optimal.
// Please don't change them without doing thorough performance
// testing.
private const int CutoverPoint = 9;

30. • Should you always use Dictionary<K,V> instead of IDictionary<K,V>?
• Should you always use structs instead of classes?
• Should you always use for instead of foreach?
• Should you always use StringBuilder instead of concatenation?
• Should you always use traditional loops instead of Linq?
• Should you always avoid throwing exceptions?
@davidwengier

31. • Should you always use Dictionary<K,V> instead of IDictionary<K,V>? No, it depends.
• Should you always use structs instead of classes? No, it depends.
• Should you always use for instead of foreach? No, it depends.
• Should you always use StringBuilder instead of concatenation? No, it depends.
• Should you always use traditional loops instead of Linq? No, it depends.
• Should you always avoid throwing exceptions? No, it depends.
• Should you always … anything? No, it probably depends.
@davidwengier

32. @davidwengier