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🌳 Sustainable Code - Small Hotpath Methods 📊

This example shows how to improve the performance of methods with the help of local functions. Inlining is an optimization

In this case, the contents of the local functions are detached from the actual method ("AnyHotPathMethod") and moved into a compiler-generated method. Thus the "HotPathMethod" is smaller and the compiler has the possibility to inline.

// Generated code without local function
public void AnyHotPathMethod()
{
    if (_b1)
    {
        _sb.Append("aaa");
    }
    if (_b2)
    {
        _sb.Append("bbb");
    }
}

// Generated code with local function
public void AnyHotPathMethodWithFunction()
{
    if (_b1)
    {
        <AnyHotPathMethodWithFunction>g__Core|4_0();
    }
    if (_b2)
    {
        <AnyHotPathMethodWithFunction>g__Core|4_1();
    }
}

[CompilerGenerated]
private void <AnyHotPathMethodWithFunction>g__Core|4_0()
{
    _sb.Append("aaa");
}

[CompilerGenerated]
private void <AnyHotPathMethodWithFunction>g__Core|4_1()
{
    _sb.Append("bbb");
}

🔥 Benchmark

BenchmarkDotNet v0.14.0, Windows 10 (10.0.19045.5131/22H2/2022Update)
AMD Ryzen 9 9950X, 1 CPU, 32 logical and 16 physical cores
.NET SDK 9.0.100
  [Host]   : .NET 9.0.0 (9.0.24.52809), X64 RyuJIT AVX-512F+CD+BW+DQ+VL+VBMI
  .NET 7.0 : .NET 7.0.20 (7.0.2024.26716), X64 RyuJIT AVX2
  .NET 8.0 : .NET 8.0.11 (8.0.1124.51707), X64 RyuJIT AVX-512F+CD+BW+DQ+VL+VBMI
  .NET 9.0 : .NET 9.0.0 (9.0.24.52809), X64 RyuJIT AVX-512F+CD+BW+DQ+VL+VBMI


| Method       | Runtime  | Iterations | Mean         | Error      | StdDev     | Ratio |
|------------- |--------- |----------- |-------------:|-----------:|-----------:|------:|
| WithoutLocal | .NET 7.0 | 10         |    11.076 ns |  0.1264 ns |  0.1121 ns |  3.94 |
| WithoutLocal | .NET 8.0 | 10         |     2.791 ns |  0.0315 ns |  0.0295 ns |  0.99 |
| WithoutLocal | .NET 9.0 | 10         |     2.812 ns |  0.0181 ns |  0.0151 ns |  1.00 |
|              |          |            |              |            |            |       |
| WithLocal    | .NET 7.0 | 10         |     3.494 ns |  0.0859 ns |  0.0990 ns |  1.24 |
| WithLocal    | .NET 8.0 | 10         |     2.807 ns |  0.0147 ns |  0.0130 ns |  0.99 |
| WithLocal    | .NET 9.0 | 10         |     2.827 ns |  0.0277 ns |  0.0246 ns |  1.00 |
|              |          |            |              |            |            |       |
| WithoutLocal | .NET 7.0 | 100        |   119.236 ns |  1.5937 ns |  1.4907 ns |  4.91 |
| WithoutLocal | .NET 8.0 | 100        |    25.734 ns |  0.1918 ns |  0.1794 ns |  1.06 |
| WithoutLocal | .NET 9.0 | 100        |    24.262 ns |  0.2096 ns |  0.1960 ns |  1.00 |
|              |          |            |              |            |            |       |
| WithLocal    | .NET 7.0 | 100        |    40.118 ns |  0.8185 ns |  0.8758 ns |  1.64 |
| WithLocal    | .NET 8.0 | 100        |    25.077 ns |  0.3515 ns |  0.3288 ns |  1.03 |
| WithLocal    | .NET 9.0 | 100        |    24.466 ns |  0.2786 ns |  0.2606 ns |  1.00 |
|              |          |            |              |            |            |       |
| WithoutLocal | .NET 7.0 | 1000       | 1,135.122 ns | 17.3263 ns | 16.2071 ns |  4.74 |
| WithoutLocal | .NET 8.0 | 1000       |   250.022 ns |  1.5989 ns |  1.4174 ns |  1.04 |
| WithoutLocal | .NET 9.0 | 1000       |   239.307 ns |  1.5506 ns |  1.4504 ns |  1.00 |
|              |          |            |              |            |            |       |
| WithLocal    | .NET 7.0 | 1000       |   330.232 ns |  5.3309 ns |  4.9866 ns |  1.37 |
| WithLocal    | .NET 8.0 | 1000       |   241.045 ns |  2.0723 ns |  1.9384 ns |  1.00 |
| WithLocal    | .NET 9.0 | 1000       |   241.217 ns |  1.8586 ns |  1.6476 ns |  1.00 |

🏁 Results

  • 🚀 The local functions are x3 faster

Remarks

  • Local functions do not make sense everywhere and also not with every hot path method
  • However, for methods with simple decisions and subsequent actions, this method has proven to be very effective.
  • All cases are at least twice, sometimes three times as performant in .NET 8.

⌨️ Run this sample

dotnet run -c Release --framework net9.0

Updates

  • 2023/11 - Add .NET 8
  • 2024/11 - Add .NET 9

Thanks to gfoidl.