C#: How do you profile performance in .NET applications?

1[MemoryDiagnoser]
2public class StringBenchmarks
3{
4    [Benchmark]
5    public string StringConcat()
6    {
7        string s = "";
8        for (int i = 0; i < 100; i++) s += "a";
9        return s;
10    }
11
12    [Benchmark]
13    public string StringBuilder()
14    {
15        var sb = new StringBuilder();
16        for (int i = 0; i < 100; i++) sb.Append("a");
17        return sb.ToString();
18    }
19}