Is Datetime.Now the Best Way to Measure a Function'S Performance

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

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.

Stopwatch vs. using System.DateTime.Now for timing events

As per MSDN:

The Stopwatch measures elapsed time by counting timer ticks in the underlying timer mechanism. If the installed hardware and operating system support a high-resolution performance counter, then the Stopwatch class uses that counter to measure elapsed time. Otherwise, the Stopwatch class uses the system timer to measure elapsed time. Use the Frequency and IsHighResolution fields to determine the precision and resolution of the Stopwatch timing implementation.

It uses a higher resolution / precision than DateTime.Now.

You can also check out these related links:

Environment.TickCount vs DateTime.Now

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

DateTime is good enough for precision to the second probably but anything beyond that I would recommend StopWatch.

What is the best way to measure execution time of a function?

System.Environment.TickCount and the System.Diagnostics.Stopwatch class are two that work well for finer resolution and straightforward usage.

C# - most efficient way of measuring ellapsed time

Don't worry. Measuring a time span does not use any resources, as it just compares now with then.

DateTime start = DateTime.Now;

// do some heavy calculation

TimeSpan delta = DateTime.Now - start; // get the time that elapsed

This does not use any resources except the variable for the start, which is just a 64 bit counter.

Note that for short timespans you're better off using Stopwatch, as this is not subject to time adjustments that may happen between start and now.

Exact time measurement for performance testing

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);

How to measure code performance in .NET?

The Stopwatch class, available since .NET 2.0, is the best way to go for this. It is a very high performance counter accurate to fractions of a millisecond.
Take a look at the MSDN documentation, which is pretty clear.

EDIT: As previously suggested, it is also advisable to run your code a number of times in order to get a reasonable average time.

Measuring code execution time

A better way would be to use Stopwatch, instead of DateTime differences.

Stopwatch Class - Microsoft Docs

Provides a set of methods and properties that you can use to
accurately measure elapsed time.

// create and start a Stopwatch instance
Stopwatch stopwatch = Stopwatch.StartNew(); 

// replace with your sample code:
System.Threading.Thread.Sleep(500);

stopwatch.Stop();
Console.WriteLine(stopwatch.ElapsedMilliseconds);

Environment.TickCount vs DateTime.Now

Use Stopwatch class. There is a decent example on msdn: http://msdn.microsoft.com/en-us/library/system.diagnostics.stopwatch.aspx

    Stopwatch stopWatch = Stopwatch.StartNew();
    Thread.Sleep(10000);
    stopWatch.Stop();
    // Get the elapsed time as a TimeSpan value.
    TimeSpan ts = stopWatch.Elapsed;

How can i calculate the speed the method is call using DateTime.Now?

Use StopWatch

Example:

Stopwatch stopWatch = new Stopwatch();
stopWatch.Start();
Thread.Sleep(10000);// or whatever code you want to calculate elapsed time.
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("RunTime " + elapsedTime);

Why are DateTime.Now DateTime.UtcNow so slow/expensive

TickCount just reads a constantly increasing counter. It's just about the simplest thing you can do.

DateTime.UtcNow needs to query the system time - and don't forget that while TickCount is blissfully ignorant of things like the user changing the clock, or NTP, UtcNow has to take this into account.

Now you've expressed a performance concern - but in the examples you've given, all you're doing is incrementing a counter. I would expect that in your real code, you'll be doing rather more work than that. If you're doing a significant amount of work, that's likely to dwarf the time taken by UtcNow. Before doing anything else, you should measure that to find out whether you're actually trying to solve a problem which doesn't exist.

If you do need to improve things, then:

You can use a timer rather than creating a new thread explicitly. There are various kinds of timers in the framework, and without knowing your exact situation, I can't advise on which would be most sensible to use - but it feels like a better solution than starting a thread.
You can measure a few iterations of your task, then guess how many will actually be required. You might want to then execute half that many iterations, take stock of how long that's taken, then adjust the number of remaining cycles accordingly. Of course, this doesn't work if the time take per iteration can vary wildly.

Is Datetime.Now the Best Way to Measure a Function'S Performance