Is DateTime.Now the best way to measure a function's performance?

c# .net performance datetime timer
David Basarab picture David Basarab · Aug 26, 2008 · Viewed 66.8k times · Source

I need to find a bottleneck and need to accurately as possible measure time.

Is the following code snippet the best way to measure the performance?

DateTime startTime = DateTime.Now;

// Some execution process

DateTime endTime = DateTime.Now;
TimeSpan totalTimeTaken = endTime.Subtract(startTime);

Answer

Markus Olsson picture Markus Olsson · Aug 26, 2008

No, it's not. Use the Stopwatch (in System.Diagnostics)

Stopwatch sw = Stopwatch.StartNew();
PerformWork();
sw.Stop();

Console.WriteLine("Time taken: {0}ms", sw.Elapsed.TotalMilliseconds);

Stopwatch automatically checks for the existence of high-precision timers.

It is worth mentioning that DateTime.Now often is quite a bit slower than DateTime.UtcNow due to the work that has to be done with timezones, DST and such.

DateTime.UtcNow typically has a resolution of 15 ms. See John Chapman's blog post about DateTime.Now precision for a great summary.

Interesting trivia: The stopwatch falls back on DateTime.UtcNow if your hardware doesn't support a high frequency counter. You can check to see if Stopwatch uses hardware to achieve high precision by looking at the static field Stopwatch.IsHighResolution.

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