在编译32位和64位时有巨大的性能差异(快26倍)

在访问值类型和引用类型列表时，我试图测量使用 for和 foreach的区别。

我使用以下类进行分析。

public static class Benchmarker
{
public static void Profile(string description, int iterations, Action func)
{
Console.Write(description);


// Warm up
func();


Stopwatch watch = new Stopwatch();


// Clean up
GC.Collect();
GC.WaitForPendingFinalizers();
GC.Collect();


watch.Start();
for (int i = 0; i < iterations; i++)
{
func();
}
watch.Stop();


Console.WriteLine(" average time: {0} ms", watch.Elapsed.TotalMilliseconds / iterations);
}
}

我使用 double作为值类型。 我创建了这个“假类”来测试引用类型:

class DoubleWrapper
{
public double Value { get; set; }


public DoubleWrapper(double value)
{
Value = value;
}
}

最后，我运行了这段代码并比较了时间差异。

static void Main(string[] args)
{
int size = 1000000;
int iterationCount = 100;


var valueList = new List<double>(size);
for (int i = 0; i < size; i++)
valueList.Add(i);


var refList = new List<DoubleWrapper>(size);
for (int i = 0; i < size; i++)
refList.Add(new DoubleWrapper(i));


double dummy;


Benchmarker.Profile("valueList for: ", iterationCount, () =>
{
double result = 0;
for (int i = 0; i < valueList.Count; i++)
{
unchecked
{
var temp = valueList[i];
result *= temp;
result += temp;
result /= temp;
result -= temp;
}
}
dummy = result;
});


Benchmarker.Profile("valueList foreach: ", iterationCount, () =>
{
double result = 0;
foreach (var v in valueList)
{
var temp = v;
result *= temp;
result += temp;
result /= temp;
result -= temp;
}
dummy = result;
});


Benchmarker.Profile("refList for: ", iterationCount, () =>
{
double result = 0;
for (int i = 0; i < refList.Count; i++)
{
unchecked
{
var temp = refList[i].Value;
result *= temp;
result += temp;
result /= temp;
result -= temp;
}
}
dummy = result;
});


Benchmarker.Profile("refList foreach: ", iterationCount, () =>
{
double result = 0;
foreach (var v in refList)
{
unchecked
{
var temp = v.Value;
result *= temp;
result += temp;
result /= temp;
result -= temp;
}
}


dummy = result;
});


SafeExit();
}

我选择 Release和 Any CPU选项，运行程序，得到以下时间:

valueList for:  average time: 483,967938 ms
valueList foreach:  average time: 477,873079 ms
refList for:  average time: 490,524197 ms
refList foreach:  average time: 485,659557 ms
Done!

然后我选择 Releaseandx64选项，运行程序，得到以下时间:

valueList for:  average time: 16,720209 ms
valueList foreach:  average time: 15,953483 ms
refList for:  average time: 19,381077 ms
refList foreach:  average time: 18,636781 ms
Done!

为什么 x64位版本的速度这么快? 我期待一些不同，但没有这么大的东西。

我没有其他电脑的权限。你能在你的机器上运行这个并告诉我结果吗？我使用的是 VisualStudio2015，我有一个英特尔 核心 I7930。

这是 SafeExit()方法，所以你可以自己编译/运行:

private static void SafeExit()
{
Console.WriteLine("Done!");
Console.ReadLine();
System.Environment.Exit(1);
}

按照要求，使用 double?代替我的 DoubleWrapper:

任何中央处理器

valueList for:  average time: 482,98116 ms
valueList foreach:  average time: 478,837701 ms
refList for:  average time: 491,075915 ms
refList foreach:  average time: 483,206072 ms
Done!

X64

valueList for:  average time: 16,393947 ms
valueList foreach:  average time: 15,87007 ms
refList for:  average time: 18,267736 ms
refList foreach:  average time: 16,496038 ms
Done!

最后但并非最不重要的: 创建 x86配置文件给我的结果与使用 Any CPU 几乎相同。