Measure execution time in C#

Question

I want to measure the execution of a piece of code and I'm wondering what the best method to do this is?

Option 1:

DateTime StartTime = DateTime.Now;  //Code  TimeSpan ts = DateTime.Now.Subtract(StartTime); string elapsedTime = String.Format("{0:00}:{1:00}:{2:00}.{3:00}",         ts.Hours, ts.Minutes, ts.Seconds,         ts.Milliseconds / 10); Console.WriteLine(elapsedTime, "RunTime"); 

Option 2: using System.Diagnostics;

    Stopwatch stopWatch = new Stopwatch();     stopWatch.Start();      //Code      stopWatch.Stop();     // Get the elapsed time as a TimeSpan value.     TimeSpan ts = stopWatch.Elapsed;      // Format and display the TimeSpan value.     string elapsedTime = String.Format("{0:00}:{1:00}:{2:00}.{3:00}",         ts.Hours, ts.Minutes, ts.Seconds,         ts.Milliseconds / 10);     Console.WriteLine(elapsedTime, "RunTime"); 

This isn't simply for benchmarking, its actually part of the application. The time the function takes to execute is relevant data. It doesn't however need to be atomic or hyper-accurate.

Which option is better for production code, or does anybody else use something different and perhaps better?

Answer 1

The Stopwatch class is specifically designed to measure elapsed time and may (if available on your hardware) provide good granularity/accuracy using an underlying high-frequency hardware timer. So this seem the best choice.

The IsHighResolution property can be used to determine whether high resolution timing is available. Per the documentation, this class offers a wrapper on the 'best available' Win32 APIs for accurate timing:

Specifically, the Frequency field and GetTimestamp method can be used in place of the unmanaged Win32 APIs QueryPerformanceFrequency and QueryPerformanceCounter.

There is detailed background on those Win32 APIs [here] and in linked MSDN docs 2.

High-Resolution Timer

A counter is a general term used in programming to refer to an incrementing variable. Some systems include a high-resolution performance counter that provides high-resolution elapsed times.

If a high-resolution performance counter exists on the system, you can use the QueryPerformanceFrequency function to express the frequency, in counts per second. The value of the count is processor dependent. On some processors, for example, the count might be the cycle rate of the processor clock.

The QueryPerformanceCounter function retrieves the current value of the high-resolution performance counter. By calling this function at the beginning and end of a section of code, an application essentially uses the counter as a high-resolution timer. For example, suppose that QueryPerformanceFrequency indicates that the frequency of the high-resolution performance counter is 50,000 counts per second. If the application calls QueryPerformanceCounter immediately before and immediately after the section of code to be timed, the counter values might be 1500 counts and 3500 counts, respectively. These values would indicate that .04 seconds (2000 counts) elapsed while the code executed.

Answer 2

It's not just that StopWatch is more accurate, but also that DateTime.Now will give incorrect results in some circumstances.

Consider what happens during a daylight saving time switch-over, for example — using DateTime.Now can actually give a negative answer!