Stopwatch Performance

Program.cs

using BenchmarkDotNet.Attributes;
using BenchmarkDotNet.Running;
using System;
using System.Diagnostics;

namespace ConsoleApp37
{
    class Program
    {
        static void Main(string[] args)
        {
            BenchmarkRunner.Run<Watcher>();
        }
    }

    [MemoryDiagnoser]
    public class Watcher
    {
        private static readonly double TimestampToTicks = TimeSpan.TicksPerSecond / (double)Stopwatch.Frequency;

        [Benchmark]
        public TimeSpan Ctor()
        {
            Stopwatch watch = new Stopwatch();
            watch.Start();
            watch.Stop();
            return watch.Elapsed;
        }

        [Benchmark]
        public TimeSpan Calc()
        {
            long start = Stopwatch.GetTimestamp();
            var now = Stopwatch.GetTimestamp();
            return new TimeSpan((long)(TimestampToTicks * (now - start)));
        }
    }
}

Results.md

BenchmarkDotNet=v0.10.9, OS=Windows 10 Redstone 1 (10.0.14393)
Processor=Intel Core i7-4870HQ CPU 2.50GHz (Haswell), ProcessorCount=8
Frequency=2435764 Hz, Resolution=410.5488 ns, Timer=TSC
.NET Core SDK=2.0.0-preview2-006497
  [Host]     : .NET Core 1.1.2 (Framework 4.6.25211.01), 64bit RyuJIT
  DefaultJob : .NET Core 1.1.2 (Framework 4.6.25211.01), 64bit RyuJIT

Method	Mean	Error	StdDev	Gen 0	Allocated
Ctor	43.05 ns	0.2424 ns	0.2149 ns	0.0063	40 B
Calc	33.16 ns	0.6466 ns	0.6048 ns	-	0 B