問題描述
DateTime.Now 是衡量函數性能的最佳方法嗎？ (Is DateTime.Now the best way to measure a function's performance?)
我需要找到一個瓶頸，並且需要盡可能準確地測量時間。
以下代碼片段是衡量性能的最佳方法嗎？
DateTime startTime = DateTime.Now;
// Some execution process
DateTime endTime = DateTime.Now;
TimeSpan totalTimeTaken = endTime.Subtract(startTime);
參考解法
方法 1:
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.
方法 2:
If you want something quick and dirty I would suggest using Stopwatch instead for a greater degree of precision.
Stopwatch sw = new Stopwatch();
sw.Start();
// Do Work
sw.Stop();
Console.WriteLine("Elapsed time: {0}", sw.Elapsed.TotalMilliseconds);
Alternatively, if you need something a little more sophisticated you should probably consider using a 3rd party profiler such as ANTS.
方法 3:
This article says that first of all you need to compare three alternatives, Stopwatch, DateTime.Now AND DateTime.UtcNow.
It also shows that in some cases (when performance counter doesn't exist) Stopwatch is using DateTime.UtcNow + some extra processing. Because of that it's obvious that in that case DateTime.UtcNow is the best option (because other use it + some processing)
However, as it turns out, the counter almost always exists ‑ see Explanation about high‑resolution performance counter and its existence related to .NET Stopwatch?.
Here is a performance graph. Notice how low performance cost UtcNow has compared to alternatives:
The X axis is sample data size, and the Y axis is the relative time of the example.
One thing Stopwatch is better at is that it provides higher resolution time measurements. Another is its more OO nature. However, creating an OO wrapper around UtcNow can't be hard.
方法 4:
It's useful to push your benchmarking code into a utility class/method. The StopWatch class does not need to be Disposed or Stopped on error. So, the simplest code to time some action is
public partial class With
{
public static long Benchmark(Action action)
{
var stopwatch = Stopwatch.StartNew();
action();
stopwatch.Stop();
return stopwatch.ElapsedMilliseconds;
}
}
Sample calling code
public void Execute(Action action)
{
var time = With.Benchmark(action);
log.DebugFormat(“Did action in {0} ms.”, time);
}
Here is the extension method version
public static class Extensions
{
public static long Benchmark(this Action action)
{
return With.Benchmark(action);
}
}
And sample calling code
public void Execute(Action action)
{
var time = action.Benchmark()
log.DebugFormat(“Did action in {0} ms.”, time);
}
方法 5:
The stopwatch functionality would be better (higher precision). I'd also recommend just downloading one of the popular profilers, though (DotTrace and ANTS are the ones I've used the most... the free trial for DotTrace is fully functional and doesn't nag like some of the others).
(by David Basarab、Markus Olsson、mmcdole、Valentin Kuzub、Anthony Mastrean、jsight)