C#: Exact time measurement for performance testing

Question

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?

Answer 1

Use the Stopwatch class

Answer 2

A better way is to use the Stopwatch class:

Stopwatch sw = new Stopwatch();

sw.Start();

// ...

sw.Stop();

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

Answer 3

System.Diagnostics.Stopwatch is designed for this task.

Answer 4

Yes there are some function on Windows kernel

 [System.Runtime.InteropServices.DllImport("KERNEL32")]
 private static extern bool QueryPerformanceCounter(  ref long lpPerformanceCount);

 [System.Runtime.InteropServices.DllImport("KERNEL32")]
 private static extern bool QueryPerformanceFrequency( ref long lpFrequency);


public static float CurrentSecond
     {
      get
      {
       long current = 0;
       QueryPerformanceCounter(ref current);
       long frequency = 0;
       QueryPerformanceFrequency(ref frequency);
       return (float) current / (float) frequency;
      }
     }

Answer 5

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.

Answer 6

Stopwatch is fine, but loop the work 10^6 times, then divide by 10^6. You'll get a lot more precision.