Program.cs

using BenchmarkDotNet.Attributes;
using BenchmarkDotNet.Running;
using Threading.Tasks;

public static class Program
{
    static void Main(string[] args)
    {
        var summary = BenchmarkRunner.Run<Bench>();
    }

    [ThreadingDiagnoser]
    public class Bench
    {
        [Params(10, 100, 1000, 10_000)]
        public int Repeat;

        [Benchmark]
        public void Lock()
        {
            var a = new Lock();
            var tasks = new Task[Repeat];
            for (int i = 0; i < Repeat; i++)
            {
                tasks[i] = a.SomeMethod();
            }
            Task.WaitAll(tasks);
            a.Assert(Repeat);
        }

        [Benchmark]
        public void QueueExample()
        {
            var a = new SerialQueueExample();
            var tasks = new Task[Repeat];
            for (int i = 0; i < Repeat; i++)
            {
                tasks[i] = a.SomeMethod();
            }
            Task.WaitAll(tasks);
            a.Assert(Repeat);
        }

    }

    class Lock
    {
        readonly object locker = new object();
        private int counter = 0;

        public async Task SomeMethod()
        {
            lock (locker)
            {
                counter++;
            }
        }

        public void Assert(int input)
        {
            if (input != counter)
            {
                throw new InvalidOperationException($"Input {input}, counter {counter}");
            }
        }
    }

    class SerialQueueExample
    {
        readonly SerialQueue queue = new SerialQueue();
        private int counter = 0;

        public async Task SomeMethod()
        {
            await queue.Enqueue(() => {
                counter++;
            });
        }

        public void Assert(int input)
        {
            if (input != counter)
            {
                throw new InvalidOperationException($"Input {input}, counter {counter}");
            }
        }
    }
}

Method	Repeat	Mean	Error	StdDev	Completed Work Items	Lock Contentions
Lock	10	286.3 ns	4.70 ns	4.39 ns	-	-
QueueExample	10	3,286.7 ns	11.63 ns	10.88 ns	1.0432	0.0000
Lock	100	2,643.7 ns	9.04 ns	7.55 ns	-	-
QueueExample	100	18,457.2 ns	126.04 ns	117.89 ns	1.1713	-
Lock	1000	26,740.9 ns	404.33 ns	378.21 ns	-	-
QueueExample	1000	442,683.7 ns	5,938.82 ns	5,555.17 ns	1.0229	-
Lock	10000	266,280.9 ns	2,956.81 ns	2,765.81 ns	-	-
QueueExample	10000	2,650,321.9 ns	55,982.63 ns	165,066.06 ns	2.6875	-