.NET Benchmarking with BenchmarkDotNet

Requires using BenchmarkDotNet.Attributes; / using BenchmarkDotNet.Running; (package BenchmarkDotNet, from NuGet). The JIT applies deeper optimizations only after code runs "hot" for a while, so a plain Stopwatch around one call misrepresents steady-state performance — BenchmarkDotNet runs enough iterations across pipeline/warmup/actual stages to account for this.

Setup

1. Create a console app, add the BenchmarkDotNet package.
2. Replace Program.cs:

using BenchmarkDotNet.Running;

BenchmarkSwitcher.FromAssembly(typeof(Program).Assembly).Run(args);

3. Run in Release, without a debugger: dotnet run -c Release. Pick which benchmark(s) to run from the printed menu.

Writing a Benchmark

[MemoryDiagnoser]
public class ListBenchmarks
{
    List<int> list;

    [Params(10, 1_000)]
    public int Count { get; set; }

    [GlobalSetup]
    public void GlobalSetup() => list = Enumerable.Range(0, Count).ToList();

    [Benchmark(Baseline = true)]
    public int Foreach()
    {
        var sum = 0;
        foreach (var item in list) sum += item;
        return sum;   // always return computed results — otherwise the JIT may eliminate the loop
    }

    [Benchmark]
    public int Foreach_AsSpan()
    {
        var sum = 0;
        foreach (var item in CollectionsMarshal.AsSpan(list)) sum += item;
        return sum;
    }
}

One [Benchmark(Baseline = true)] per class (or per category) anchors the Ratio column. [Params] on a property multiplies every benchmark across each listed value, populated via [GlobalSetup] (inline field init would run before Count is assigned).

Reference Files

File	Load When
references/writing-benchmarks.md	Project setup detail, benchmark attribute reference ([Benchmark], [Params], [GlobalSetup]/[GlobalCleanup]), avoiding JIT dead-code elimination
references/interpreting-results.md	Results table columns, [MemoryDiagnoser] allocation columns, [BenchmarkCategory]/[GroupBenchmarksBy]/[HideColumns], artifact file locations
references/comparing-configurations.md	Multi-job ManualConfig classes, comparing .NET runtimes/versions with AddJob/WithRuntime, custom environment-variable jobs, RatioStyle.Trend
references/runtime-variant-testing.md	Testing code under environment-variable variants outside benchmarks: .runsettings files, dotnet test -e/-s, Visual Studio run-settings selection