c# framework 为什么操作员比方法调用慢得多?(结构只在较早的JIT上变慢)



facts essential (7)

简介:我用C#编写高性能代码。 是的,我知道C ++会给我更好的优化,但我仍然选择使用C#。 我不想辩论这个选择。 相反,我想听到那些和我一样正在尝试在.NET Framework上编写高性能代码的人的消息。

问题:

  • 为什么下面的代码中的运算符比等效的方法调用慢?
  • 为什么在下面的代码中传递两个双精度比传递一个内部有两个双精度的结构的等价方法更快? (答:老JITs优化结构不好)
  • 有没有办法让.NET JIT编译器像结构体的成员那样有效地对待简单结构体? (答:得到更新的JIT)

我想我知道的是:原始的.NET JIT编译器不会内联任何涉及结构的内容。 奇怪的给定的结构只应用于需要小内存类型的应该像内置插件那样优化的情况,但这是真的。 幸运的是,在.NET 3.5SP1和.NET 2.0SP2中,他们对JIT Optimizer进行了一些改进,包括对内联的改进,特别是对结构的改进。 (我猜他们是这么做的,因为否则他们引入的新复杂结构将会执行非常糟糕的事情......所以复杂团队可能在JIT Optimizer团队中大打出手。)因此,.NET 3.5 SP1之前的任何文档都可能与这个问题不太相关。

我的测试显示:我已通过检查C:\ Windows \ Microsoft.NET \ Framework \ v2.0.50727 \ mscorwks.dll文件是否具有> = 3053版本来验证我是否具有较新的JIT Optimizer,因此应该有这些改进到JIT优化器。 然而,即便如此,我的时间表和看起来反汇编都显示的是:

JIT生成的用于传递两个双精度结构的代码比直接传递两个双精度的代码效率低得多。

与传递结构作为参数相比,JIT为结构体方法生成的代码传入“this”的效率要高得多。

如果你传递两个双打而不是传递一个带有两个双打结构的JIT,那么JIT仍然会更好,即使乘法器显然处于循环中也是如此。

定时:实际上,在反汇编中,我意识到循环中的大部分时间只是从列表中访问测试数据。 如果将循环的开销代码和数据的访问分解出来,那么进行相同调用的四种方式之间的区别会大不相同。 我可以从5倍到20倍的任何地方获得PlusEqual(double,double)而不是PlusEqual(Element)。 并且10x到40x用于执行PlusEqual(double,double)而不是operator + =。 哇。 伤心。

以下是一组计时:

Populating List<Element> took 320ms.
The PlusEqual() method took 105ms.
The 'same' += operator took 131ms.
The 'same' -= operator took 139ms.
The PlusEqual(double, double) method took 68ms.
The do nothing loop took 66ms.
The ratio of operator with constructor to method is 124%.
The ratio of operator without constructor to method is 132%.
The ratio of PlusEqual(double,double) to PlusEqual(Element) is 64%.
If we remove the overhead time for the loop accessing the elements from the List...
The ratio of operator with constructor to method is 166%.
The ratio of operator without constructor to method is 187%.
The ratio of PlusEqual(double,double) to PlusEqual(Element) is 5%.

代码:

namespace OperatorVsMethod
{
  public struct Element
  {
    public double Left;
    public double Right;

    public Element(double left, double right)
    {
      this.Left = left;
      this.Right = right;
    }

    public static Element operator +(Element x, Element y)
    {
      return new Element(x.Left + y.Left, x.Right + y.Right);
    }

    public static Element operator -(Element x, Element y)
    {
      x.Left += y.Left;
      x.Right += y.Right;
      return x;
    }    

    /// <summary>
    /// Like the += operator; but faster.
    /// </summary>
    public void PlusEqual(Element that)
    {
      this.Left += that.Left;
      this.Right += that.Right;
    }    

    /// <summary>
    /// Like the += operator; but faster.
    /// </summary>
    public void PlusEqual(double thatLeft, double thatRight)
    {
      this.Left += thatLeft;
      this.Right += thatRight;
    }    
  }    

  [TestClass]
  public class UnitTest1
  {
    [TestMethod]
    public void TestMethod1()
    {
      Stopwatch stopwatch = new Stopwatch();

      // Populate a List of Elements to multiply together
      int seedSize = 4;
      List<double> doubles = new List<double>(seedSize);
      doubles.Add(2.5d);
      doubles.Add(100000d);
      doubles.Add(-0.5d);
      doubles.Add(-100002d);

      int size = 2500000 * seedSize;
      List<Element> elts = new List<Element>(size);

      stopwatch.Reset();
      stopwatch.Start();
      for (int ii = 0; ii < size; ++ii)
      {
        int di = ii % seedSize;
        double d = doubles[di];
        elts.Add(new Element(d, d));
      }
      stopwatch.Stop();
      long populateMS = stopwatch.ElapsedMilliseconds;

      // Measure speed of += operator (calls ctor)
      Element operatorCtorResult = new Element(1d, 1d);
      stopwatch.Reset();
      stopwatch.Start();
      for (int ii = 0; ii < size; ++ii)
      {
        operatorCtorResult += elts[ii];
      }
      stopwatch.Stop();
      long operatorCtorMS = stopwatch.ElapsedMilliseconds;

      // Measure speed of -= operator (+= without ctor)
      Element operatorNoCtorResult = new Element(1d, 1d);
      stopwatch.Reset();
      stopwatch.Start();
      for (int ii = 0; ii < size; ++ii)
      {
        operatorNoCtorResult -= elts[ii];
      }
      stopwatch.Stop();
      long operatorNoCtorMS = stopwatch.ElapsedMilliseconds;

      // Measure speed of PlusEqual(Element) method
      Element plusEqualResult = new Element(1d, 1d);
      stopwatch.Reset();
      stopwatch.Start();
      for (int ii = 0; ii < size; ++ii)
      {
        plusEqualResult.PlusEqual(elts[ii]);
      }
      stopwatch.Stop();
      long plusEqualMS = stopwatch.ElapsedMilliseconds;

      // Measure speed of PlusEqual(double, double) method
      Element plusEqualDDResult = new Element(1d, 1d);
      stopwatch.Reset();
      stopwatch.Start();
      for (int ii = 0; ii < size; ++ii)
      {
        Element elt = elts[ii];
        plusEqualDDResult.PlusEqual(elt.Left, elt.Right);
      }
      stopwatch.Stop();
      long plusEqualDDMS = stopwatch.ElapsedMilliseconds;

      // Measure speed of doing nothing but accessing the Element
      Element doNothingResult = new Element(1d, 1d);
      stopwatch.Reset();
      stopwatch.Start();
      for (int ii = 0; ii < size; ++ii)
      {
        Element elt = elts[ii];
        double left = elt.Left;
        double right = elt.Right;
      }
      stopwatch.Stop();
      long doNothingMS = stopwatch.ElapsedMilliseconds;

      // Report results
      Assert.AreEqual(1d, operatorCtorResult.Left, "The operator += did not compute the right result!");
      Assert.AreEqual(1d, operatorNoCtorResult.Left, "The operator += did not compute the right result!");
      Assert.AreEqual(1d, plusEqualResult.Left, "The operator += did not compute the right result!");
      Assert.AreEqual(1d, plusEqualDDResult.Left, "The operator += did not compute the right result!");
      Assert.AreEqual(1d, doNothingResult.Left, "The operator += did not compute the right result!");

      // Report speeds
      Console.WriteLine("Populating List<Element> took {0}ms.", populateMS);
      Console.WriteLine("The PlusEqual() method took {0}ms.", plusEqualMS);
      Console.WriteLine("The 'same' += operator took {0}ms.", operatorCtorMS);
      Console.WriteLine("The 'same' -= operator took {0}ms.", operatorNoCtorMS);
      Console.WriteLine("The PlusEqual(double, double) method took {0}ms.", plusEqualDDMS);
      Console.WriteLine("The do nothing loop took {0}ms.", doNothingMS);

      // Compare speeds
      long percentageRatio = 100L * operatorCtorMS / plusEqualMS;
      Console.WriteLine("The ratio of operator with constructor to method is {0}%.", percentageRatio);
      percentageRatio = 100L * operatorNoCtorMS / plusEqualMS;
      Console.WriteLine("The ratio of operator without constructor to method is {0}%.", percentageRatio);
      percentageRatio = 100L * plusEqualDDMS / plusEqualMS;
      Console.WriteLine("The ratio of PlusEqual(double,double) to PlusEqual(Element) is {0}%.", percentageRatio);

      operatorCtorMS -= doNothingMS;
      operatorNoCtorMS -= doNothingMS;
      plusEqualMS -= doNothingMS;
      plusEqualDDMS -= doNothingMS;
      Console.WriteLine("If we remove the overhead time for the loop accessing the elements from the List...");
      percentageRatio = 100L * operatorCtorMS / plusEqualMS;
      Console.WriteLine("The ratio of operator with constructor to method is {0}%.", percentageRatio);
      percentageRatio = 100L * operatorNoCtorMS / plusEqualMS;
      Console.WriteLine("The ratio of operator without constructor to method is {0}%.", percentageRatio);
      percentageRatio = 100L * plusEqualDDMS / plusEqualMS;
      Console.WriteLine("The ratio of PlusEqual(double,double) to PlusEqual(Element) is {0}%.", percentageRatio);
    }
  }
}

IL:(也就是上面的一些内容被编译成)

public void PlusEqual(Element that)
    {
00000000 push    ebp 
00000001 mov     ebp,esp 
00000003 push    edi 
00000004 push    esi 
00000005 push    ebx 
00000006 sub     esp,30h 
00000009 xor     eax,eax 
0000000b mov     dword ptr [ebp-10h],eax 
0000000e xor     eax,eax 
00000010 mov     dword ptr [ebp-1Ch],eax 
00000013 mov     dword ptr [ebp-3Ch],ecx 
00000016 cmp     dword ptr ds:[04C87B7Ch],0 
0000001d je     00000024 
0000001f call    753081B1 
00000024 nop       
      this.Left += that.Left;
00000025 mov     eax,dword ptr [ebp-3Ch] 
00000028 fld     qword ptr [ebp+8] 
0000002b fadd    qword ptr [eax] 
0000002d fstp    qword ptr [eax] 
      this.Right += that.Right;
0000002f mov     eax,dword ptr [ebp-3Ch] 
00000032 fld     qword ptr [ebp+10h] 
00000035 fadd    qword ptr [eax+8] 
00000038 fstp    qword ptr [eax+8] 
    }
0000003b nop       
0000003c lea     esp,[ebp-0Ch] 
0000003f pop     ebx 
00000040 pop     esi 
00000041 pop     edi 
00000042 pop     ebp 
00000043 ret     10h 
 public void PlusEqual(double thatLeft, double thatRight)
    {
00000000 push    ebp 
00000001 mov     ebp,esp 
00000003 push    edi 
00000004 push    esi 
00000005 push    ebx 
00000006 sub     esp,30h 
00000009 xor     eax,eax 
0000000b mov     dword ptr [ebp-10h],eax 
0000000e xor     eax,eax 
00000010 mov     dword ptr [ebp-1Ch],eax 
00000013 mov     dword ptr [ebp-3Ch],ecx 
00000016 cmp     dword ptr ds:[04C87B7Ch],0 
0000001d je     00000024 
0000001f call    75308159 
00000024 nop       
      this.Left += thatLeft;
00000025 mov     eax,dword ptr [ebp-3Ch] 
00000028 fld     qword ptr [ebp+10h] 
0000002b fadd    qword ptr [eax] 
0000002d fstp    qword ptr [eax] 
      this.Right += thatRight;
0000002f mov     eax,dword ptr [ebp-3Ch] 
00000032 fld     qword ptr [ebp+8] 
00000035 fadd    qword ptr [eax+8] 
00000038 fstp    qword ptr [eax+8] 
    }
0000003b nop       
0000003c lea     esp,[ebp-0Ch] 
0000003f pop     ebx 
00000040 pop     esi 
00000041 pop     edi 
00000042 pop     ebp 
00000043 ret     10h 

Answer #1

我很难复制你的结果。

我把你的代码:

  • 使其成为独立的控制台应用程序
  • 构建了一个优化(发布)构建
  • 将“规模”因素从2.5M提高到了10M
  • 从命令行(IDE外部)运行它,

当我这样做时,我得到了以下与您的截然不同的时间。 为了避免疑惑,我会张贴我使用的代码。

这是我的时间

Populating List<Element> took 527ms.
The PlusEqual() method took 450ms.
The 'same' += operator took 386ms.
The 'same' -= operator took 446ms.
The PlusEqual(double, double) method took 413ms.
The do nothing loop took 229ms.
The ratio of operator with constructor to method is 85%.
The ratio of operator without constructor to method is 99%.
The ratio of PlusEqual(double,double) to PlusEqual(Element) is 91%.
If we remove the overhead time for the loop accessing the elements from the List...
The ratio of operator with constructor to method is 71%.
The ratio of operator without constructor to method is 98%.
The ratio of PlusEqual(double,double) to PlusEqual(Element) is 83%.

这些是我对你的代码的编辑:

namespace OperatorVsMethod
{
  public struct Element
  {
    public double Left;
    public double Right;

    public Element(double left, double right)
    {
      this.Left = left;
      this.Right = right;
    }    

    public static Element operator +(Element x, Element y)
    {
      return new Element(x.Left + y.Left, x.Right + y.Right);
    }

    public static Element operator -(Element x, Element y)
    {
      x.Left += y.Left;
      x.Right += y.Right;
      return x;
    }    

    /// <summary>
    /// Like the += operator; but faster.
    /// </summary>
    public void PlusEqual(Element that)
    {
      this.Left += that.Left;
      this.Right += that.Right;
    }    

    /// <summary>
    /// Like the += operator; but faster.
    /// </summary>
    public void PlusEqual(double thatLeft, double thatRight)
    {
      this.Left += thatLeft;
      this.Right += thatRight;
    }    
  }    

  public class UnitTest1
  {
    public static void Main()
    {
      Stopwatch stopwatch = new Stopwatch();

      // Populate a List of Elements to multiply together
      int seedSize = 4;
      List<double> doubles = new List<double>(seedSize);
      doubles.Add(2.5d);
      doubles.Add(100000d);
      doubles.Add(-0.5d);
      doubles.Add(-100002d);

      int size = 10000000 * seedSize;
      List<Element> elts = new List<Element>(size);

      stopwatch.Reset();
      stopwatch.Start();
      for (int ii = 0; ii < size; ++ii)
      {
        int di = ii % seedSize;
        double d = doubles[di];
        elts.Add(new Element(d, d));
      }
      stopwatch.Stop();
      long populateMS = stopwatch.ElapsedMilliseconds;

      // Measure speed of += operator (calls ctor)
      Element operatorCtorResult = new Element(1d, 1d);
      stopwatch.Reset();
      stopwatch.Start();
      for (int ii = 0; ii < size; ++ii)
      {
        operatorCtorResult += elts[ii];
      }
      stopwatch.Stop();
      long operatorCtorMS = stopwatch.ElapsedMilliseconds;

      // Measure speed of -= operator (+= without ctor)
      Element operatorNoCtorResult = new Element(1d, 1d);
      stopwatch.Reset();
      stopwatch.Start();
      for (int ii = 0; ii < size; ++ii)
      {
        operatorNoCtorResult -= elts[ii];
      }
      stopwatch.Stop();
      long operatorNoCtorMS = stopwatch.ElapsedMilliseconds;

      // Measure speed of PlusEqual(Element) method
      Element plusEqualResult = new Element(1d, 1d);
      stopwatch.Reset();
      stopwatch.Start();
      for (int ii = 0; ii < size; ++ii)
      {
        plusEqualResult.PlusEqual(elts[ii]);
      }
      stopwatch.Stop();
      long plusEqualMS = stopwatch.ElapsedMilliseconds;

      // Measure speed of PlusEqual(double, double) method
      Element plusEqualDDResult = new Element(1d, 1d);
      stopwatch.Reset();
      stopwatch.Start();
      for (int ii = 0; ii < size; ++ii)
      {
        Element elt = elts[ii];
        plusEqualDDResult.PlusEqual(elt.Left, elt.Right);
      }
      stopwatch.Stop();
      long plusEqualDDMS = stopwatch.ElapsedMilliseconds;

      // Measure speed of doing nothing but accessing the Element
      Element doNothingResult = new Element(1d, 1d);
      stopwatch.Reset();
      stopwatch.Start();
      for (int ii = 0; ii < size; ++ii)
      {
        Element elt = elts[ii];
        double left = elt.Left;
        double right = elt.Right;
      }
      stopwatch.Stop();
      long doNothingMS = stopwatch.ElapsedMilliseconds;

      // Report speeds
      Console.WriteLine("Populating List<Element> took {0}ms.", populateMS);
      Console.WriteLine("The PlusEqual() method took {0}ms.", plusEqualMS);
      Console.WriteLine("The 'same' += operator took {0}ms.", operatorCtorMS);
      Console.WriteLine("The 'same' -= operator took {0}ms.", operatorNoCtorMS);
      Console.WriteLine("The PlusEqual(double, double) method took {0}ms.", plusEqualDDMS);
      Console.WriteLine("The do nothing loop took {0}ms.", doNothingMS);

      // Compare speeds
      long percentageRatio = 100L * operatorCtorMS / plusEqualMS;
      Console.WriteLine("The ratio of operator with constructor to method is {0}%.", percentageRatio);
      percentageRatio = 100L * operatorNoCtorMS / plusEqualMS;
      Console.WriteLine("The ratio of operator without constructor to method is {0}%.", percentageRatio);
      percentageRatio = 100L * plusEqualDDMS / plusEqualMS;
      Console.WriteLine("The ratio of PlusEqual(double,double) to PlusEqual(Element) is {0}%.", percentageRatio);

      operatorCtorMS -= doNothingMS;
      operatorNoCtorMS -= doNothingMS;
      plusEqualMS -= doNothingMS;
      plusEqualDDMS -= doNothingMS;
      Console.WriteLine("If we remove the overhead time for the loop accessing the elements from the List...");
      percentageRatio = 100L * operatorCtorMS / plusEqualMS;
      Console.WriteLine("The ratio of operator with constructor to method is {0}%.", percentageRatio);
      percentageRatio = 100L * operatorNoCtorMS / plusEqualMS;
      Console.WriteLine("The ratio of operator without constructor to method is {0}%.", percentageRatio);
      percentageRatio = 100L * plusEqualDDMS / plusEqualMS;
      Console.WriteLine("The ratio of PlusEqual(double,double) to PlusEqual(Element) is {0}%.", percentageRatio);
    }
  }
}

Answer #2

我会想象当你访问结构的成员时,它实际上正在做一个额外的操作来访问成员,THIS指针+偏移量。


Answer #3

在这里运行.NET 4.0。 我使用“任何CPU”编译,将.NET 4.0作为发布模式。 执行来自命令行。 它以64位模式运行。 我的时间有点不同。

Populating List<Element> took 442ms.
The PlusEqual() method took 115ms.
The 'same' += operator took 201ms.
The 'same' -= operator took 200ms.
The PlusEqual(double, double) method took 129ms.
The do nothing loop took 93ms.
The ratio of operator with constructor to method is 174%.
The ratio of operator without constructor to method is 173%.
The ratio of PlusEqual(double,double) to PlusEqual(Element) is 112%.
If we remove the overhead time for the loop accessing the elements from the List
...
The ratio of operator with constructor to method is 490%.
The ratio of operator without constructor to method is 486%.
The ratio of PlusEqual(double,double) to PlusEqual(Element) is 163%.

特别是, PlusEqual(Element)PlusEqual(double, double)稍快。

无论.NET 3.5中出现什么问题,它都不会出现在.NET 4.0中。


Answer #4

像@Corey Kosak一样,我只是在发布模式下将这个代码作为一个简单的控制台应用程序在VS 2010 Express中运行。 我得到非常不同的数字。 但我也有Fx4.5,所以这些可能不是干净的Fx4.0的结果。

Populating List<Element> took 435ms.
The PlusEqual() method took 109ms.
The 'same' += operator took 217ms.
The 'same' -= operator took 157ms.
The PlusEqual(double, double) method took 118ms.
The do nothing loop took 79ms.
The ratio of operator with constructor to method is 199%.
The ratio of operator without constructor to method is 144%.
The ratio of PlusEqual(double,double) to PlusEqual(Element) is 108%.
If we remove the overhead time for the loop accessing the elements from the List
...
The ratio of operator with constructor to method is 460%.
The ratio of operator without constructor to method is 260%.
The ratio of PlusEqual(double,double) to PlusEqual(Element) is 130%.

编辑:现在从cmd行运行。 这确实有所作为,数字变化较小。


Answer #5

可以代替列表你应该使用double []和“众所周知的”偏移和索引增量?


Answer #6

我得到了非常不同的结果,更没戏剧性。 但没有使用测试跑步者,我将代码粘贴到控制台模式应用程序中。 在我尝试时,5%的结果在32位模式下为〜87%,在64位模式下为〜100%。

对齐对于双打是非常重要的,.NET运行时只能保证在32位机器上对齐4。 在我看来,测试运行者正在启动测试方法,其堆栈地址与4对齐,而不是8对齐。当双重穿越缓存行边界时,错位惩罚会变得非常大。


Answer #7

不确定这是否相关,但是这里是Windows 7 64位上.NET 4.0 64位的数字。 我的mscorwks.dll版本是2.0.50727.5446。 我只是将代码粘贴到LINQPad并从那里运行。 结果如下:

Populating List<Element> took 496ms.
The PlusEqual() method took 189ms.
The 'same' += operator took 295ms.
The 'same' -= operator took 358ms.
The PlusEqual(double, double) method took 148ms.
The do nothing loop took 103ms.
The ratio of operator with constructor to method is 156%.
The ratio of operator without constructor to method is 189%.
The ratio of PlusEqual(double,double) to PlusEqual(Element) is 78%.
If we remove the overhead time for the loop accessing the elements from the List
...
The ratio of operator with constructor to method is 223%.
The ratio of operator without constructor to method is 296%.
The ratio of PlusEqual(double,double) to PlusEqual(Element) is 52%.




jit