Exact time measurement for performance testing [duplicate]

What is the most exact way of seeing how long something, for example a method call, took in code?

The easiest and quickest I would guess is this:

DateTime start = DateTime.Now;
{
    // Do some work
}
TimeSpan timeItTook = DateTime.Now - start;

But how exact is this? Are there better ways?

Solution 1:

A better way is to use the Stopwatch class:

using System.Diagnostics;
// ...

Stopwatch sw = new Stopwatch();

sw.Start();

// ...

sw.Stop();

Console.WriteLine("Elapsed={0}",sw.Elapsed);

Solution 2:

As others have said, Stopwatch is a good class to use here. You can wrap it in a helpful method:

public static TimeSpan Time(Action action)
{
    Stopwatch stopwatch = Stopwatch.StartNew();
    action();
    stopwatch.Stop();
    return stopwatch.Elapsed;
}

(Note the use of Stopwatch.StartNew(). I prefer this to creating a Stopwatch and then calling Start() in terms of simplicity.) Obviously this incurs the hit of invoking a delegate, but in the vast majority of cases that won't be relevant. You'd then write:

TimeSpan time = StopwatchUtil.Time(() =>
{
    // Do some work
});

You could even make an ITimer interface for this, with implementations of StopwatchTimer, CpuTimer etc where available.