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好奇心：为什么 Expression<...>编译时运行速度比最小的 DynamicMethod 更快？

发布于 2024-08-02 04:30:11 字数 2823 浏览 5 评论 0 原文

我目前正在做一些最后的优化，主要是为了乐趣和学习，并发现了一些给我留下了几个问题的东西。

首先，问题：

  1. 当我通过使用 DynamicMethod，并使用调试器，当我在反汇编器视图中查看代码时，有什么方法可以单步执行生成的汇编代码吗？调试器似乎只是为我跳过整个方法，
  2. 或者，如果不可能，我是否可以以某种方式将生成的 IL 代码作为程序集保存到磁盘，以便我可以使用 反射器？
  3. 为什么我的简单加法方法 (Int32+Int32 => Int32) 的 Expression<...> 版本比最小 DynamicMethod 版本运行得更快？

这是一个简短而完整的演示程序。在我的系统上，输出是：

DynamicMethod: 887 ms
Lambda: 1878 ms
Method: 1969 ms
Expression: 681 ms

我期望 lambda 和方法调用具有更高的值，但 DynamicMethod 版本始终慢 30-50% 左右（变化可能是由于 Windows 和其他程序造成的）。有人知道原因吗？

这是程序：

using System;
using System.Linq.Expressions;
using System.Reflection.Emit;
using System.Diagnostics;

namespace Sandbox
{
    public class Program
    {
        public static void Main(String[] args)
        {
            DynamicMethod method = new DynamicMethod("TestMethod",
                typeof(Int32), new Type[] { typeof(Int32), typeof(Int32) });
            var il = method.GetILGenerator();

            il.Emit(OpCodes.Ldarg_0);
            il.Emit(OpCodes.Ldarg_1);
            il.Emit(OpCodes.Add);
            il.Emit(OpCodes.Ret);

            Func<Int32, Int32, Int32> f1 =
                (Func<Int32, Int32, Int32>)method.CreateDelegate(
                    typeof(Func<Int32, Int32, Int32>));
            Func<Int32, Int32, Int32> f2 = (Int32 a, Int32 b) => a + b;
            Func<Int32, Int32, Int32> f3 = Sum;
            Expression<Func<Int32, Int32, Int32>> f4x = (a, b) => a + b;
            Func<Int32, Int32, Int32> f4 = f4x.Compile();
            for (Int32 pass = 1; pass <= 2; pass++)
            {
                // Pass 1 just runs all the code without writing out anything
                // to avoid JIT overhead influencing the results
                Time(f1, "DynamicMethod", pass);
                Time(f2, "Lambda", pass);
                Time(f3, "Method", pass);
                Time(f4, "Expression", pass);
            }
        }

        private static void Time(Func<Int32, Int32, Int32> fn,
            String name, Int32 pass)
        {
            Stopwatch sw = new Stopwatch();
            sw.Start();
            for (Int32 index = 0; index <= 100000000; index++)
            {
                Int32 result = fn(index, 1);
            }
            sw.Stop();
            if (pass == 2)
                Debug.WriteLine(name + ": " + sw.ElapsedMilliseconds + " ms");
        }

        private static Int32 Sum(Int32 a, Int32 b)
        {
            return a + b;
        }
    }
}
原文

I'm currently doing some last-measure optimizations, mostly for fun and learning, and discovered something that left me with a couple of questions.

First, the questions:

  1. When I construct a method in-memory through the use of DynamicMethod, and use the debugger, is there any way for me to step into the generated assembly code, when vieweing the code in the disassembler view? The debugger seems to just step over the whole method for me
  2. Or, if that's not possible, is it possible for me to somehow save the generated IL code to disk as an assembly, so that I can inspect it with Reflector?
  3. Why does the Expression<...> version of my simple addition method (Int32+Int32 => Int32) run faster than a minimal DynamicMethod version?

Here's a short and complete program that demonstrates. On my system, the output is:

DynamicMethod: 887 ms
Lambda: 1878 ms
Method: 1969 ms
Expression: 681 ms

I expected the lambda and method calls to have higher values, but the DynamicMethod version is consistently about 30-50% slower (variations probably due to Windows and other programs). Anyone know the reason?

Here's the program:

using System;
using System.Linq.Expressions;
using System.Reflection.Emit;
using System.Diagnostics;

namespace Sandbox
{
    public class Program
    {
        public static void Main(String[] args)
        {
            DynamicMethod method = new DynamicMethod("TestMethod",
                typeof(Int32), new Type[] { typeof(Int32), typeof(Int32) });
            var il = method.GetILGenerator();

            il.Emit(OpCodes.Ldarg_0);
            il.Emit(OpCodes.Ldarg_1);
            il.Emit(OpCodes.Add);
            il.Emit(OpCodes.Ret);

            Func<Int32, Int32, Int32> f1 =
                (Func<Int32, Int32, Int32>)method.CreateDelegate(
                    typeof(Func<Int32, Int32, Int32>));
            Func<Int32, Int32, Int32> f2 = (Int32 a, Int32 b) => a + b;
            Func<Int32, Int32, Int32> f3 = Sum;
            Expression<Func<Int32, Int32, Int32>> f4x = (a, b) => a + b;
            Func<Int32, Int32, Int32> f4 = f4x.Compile();
            for (Int32 pass = 1; pass <= 2; pass++)
            {
                // Pass 1 just runs all the code without writing out anything
                // to avoid JIT overhead influencing the results
                Time(f1, "DynamicMethod", pass);
                Time(f2, "Lambda", pass);
                Time(f3, "Method", pass);
                Time(f4, "Expression", pass);
            }
        }

        private static void Time(Func<Int32, Int32, Int32> fn,
            String name, Int32 pass)
        {
            Stopwatch sw = new Stopwatch();
            sw.Start();
            for (Int32 index = 0; index <= 100000000; index++)
            {
                Int32 result = fn(index, 1);
            }
            sw.Stop();
            if (pass == 2)
                Debug.WriteLine(name + ": " + sw.ElapsedMilliseconds + " ms");
        }

        private static Int32 Sum(Int32 a, Int32 b)
        {
            return a + b;
        }
    }
}

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晚雾 2024-08-09 04:30:11

通过DynamicMethod 创建的方法会经历两次重击，而通过Expression<> 创建的方法不会经历任何重击。

这是它的工作原理。 ，我将参数硬编码为 0 和 1）：

00cc032c 6a01            push    1           // 1 argument
00cc032e 8bcf            mov     ecx,edi
00cc0330 33d2            xor     edx,edx     // 0 argument
00cc0332 8b410c          mov     eax,dword ptr [ecx+0Ch]
00cc0335 8b4904          mov     ecx,dword ptr [ecx+4]
00cc0338 ffd0            call    eax // 1 arg on stack, two in edx, ecx

以下是在 Time 方法中调用 fn(0, 1) 的调用顺序（为了便于调试 在我调查的调用DynamicMethod 中，call eax 行如下所示：

00cc0338 ffd0            call    eax {003c2084}
0:000> !u 003c2084
Unmanaged code
003c2084 51              push    ecx
003c2085 8bca            mov     ecx,edx
003c2087 8b542408        mov     edx,dword ptr [esp+8]
003c208b 8b442404        mov     eax,dword ptr [esp+4]
003c208f 89442408        mov     dword ptr [esp+8],eax
003c2093 58              pop     eax
003c2094 83c404          add     esp,4
003c2097 83c010          add     eax,10h
003c209a ff20            jmp     dword ptr [eax]

这似乎是在进行一些堆栈调整以重新排列参数。我推测这是由于使用隐式“this”参数的代表与不使用隐式“this”参数的代表之间的差异造成的。

最后的跳转解析如下：

003c209a ff20            jmp     dword ptr [eax]      ds:0023:012f7edc=0098c098
0098c098 e963403500      jmp     00ce0100

0098c098 处的代码的其余部分看起来像一个 JIT thunk，其开头在 JIT 之后用 jmp 重写。只有在这个跳转之后，我们才能到达真正的代码：

0:000> !u eip
Normal JIT generated code
DynamicClass.TestMethod(Int32, Int32)
Begin 00ce0100, size 5
>>> 00ce0100 03ca            add     ecx,edx
00ce0102 8bc1            mov     eax,ecx
00ce0104 c3              ret

通过Expression<>创建的方法的调用序列是不同的 - 它缺少堆栈调配代码。就是这样，从通过 eax 的第一次跳转开始：

00cc0338 ffd0            call    eax {00ce00a8}

0:000> !u eip
Normal JIT generated code
DynamicClass.lambda_method(System.Runtime.CompilerServices.ExecutionScope, Int32, Int32)
Begin 00ce00a8, size b
>>> 00ce00a8 8b442404        mov     eax,dword ptr [esp+4]
00ce00ac 03d0            add     edx,eax
00ce00ae 8bc2            mov     eax,edx
00ce00b0 c20400          ret     4

现在，事情是怎么变成这样的呢？

  1. 堆栈调配不是必需的（实际上使用了委托的隐式第一个参数，即不像绑定到静态方法的委托）
  2. 。JIT 必须由 LINQ 编译逻辑强制执行，以便委托持有真实的目标地址，而不是一个假的。

我不知道 LINQ 如何强制 JIT，但我自己知道如何强制 JIT - 通过至少调用该函数一次。更新：我找到了另一种强制 JIT 的方法：对构造函数使用 restrictedSkipVisibility 参数并传递 true。因此，这里是修改后的代码，通过使用隐式“this”参数来消除堆栈调配，并使用备用构造函数进行预编译，以便绑定地址是真实地址，而不是 thunk：

using System;
using System.Linq.Expressions;
using System.Reflection.Emit;
using System.Diagnostics;

namespace Sandbox
{
    public class Program
    {
        public static void Main(String[] args)
        {
            DynamicMethod method = new DynamicMethod("TestMethod",
                typeof(Int32), new Type[] { typeof(object), typeof(Int32),
                typeof(Int32) }, true);
            var il = method.GetILGenerator();

            il.Emit(OpCodes.Ldarg_1);
            il.Emit(OpCodes.Ldarg_2);
            il.Emit(OpCodes.Add);
            il.Emit(OpCodes.Ret);

            Func<Int32, Int32, Int32> f1 =
                (Func<Int32, Int32, Int32>)method.CreateDelegate(
                    typeof(Func<Int32, Int32, Int32>), null);
            Func<Int32, Int32, Int32> f2 = (Int32 a, Int32 b) => a + b;
            Func<Int32, Int32, Int32> f3 = Sum;
            Expression<Func<Int32, Int32, Int32>> f4x = (a, b) => a + b;
            Func<Int32, Int32, Int32> f4 = f4x.Compile();
            for (Int32 pass = 1; pass <= 2; pass++)
            {
                // Pass 1 just runs all the code without writing out anything
                // to avoid JIT overhead influencing the results
                Time(f1, "DynamicMethod", pass);
                Time(f2, "Lambda", pass);
                Time(f3, "Method", pass);
                Time(f4, "Expression", pass);
            }
        }

        private static void Time(Func<Int32, Int32, Int32> fn,
            String name, Int32 pass)
        {
            Stopwatch sw = new Stopwatch();
            sw.Start();
            for (Int32 index = 0; index <= 100000000; index++)
            {
                Int32 result = fn(index, 1);
            }
            sw.Stop();
            if (pass == 2)
                Console.WriteLine(name + ": " + sw.ElapsedMilliseconds + " ms");
        }

        private static Int32 Sum(Int32 a, Int32 b)
        {
            return a + b;
        }
    }
}

这是我系统上的运行时：

DynamicMethod: 312 ms
Lambda: 417 ms
Method: 417 ms
Expression: 312 ms

<强>更新添加：

我尝试在我的新系统上运行此代码，该系统是运行 Windows 7 x64 的 Core i7 920，安装了 .NET 4 beta 2（mscoree.dll 版本 4.0.30902），并且结果是可变的。

csc 3.5, /platform:x86, runtime v2.0.50727 (via .config)

Run #1
DynamicMethod: 214 ms
Lambda: 571 ms
Method: 570 ms
Expression: 249 ms

Run #2
DynamicMethod: 463 ms
Lambda: 392 ms
Method: 392 ms
Expression: 463 ms

Run #3
DynamicMethod: 463 ms
Lambda: 570 ms
Method: 570 ms
Expression: 463 ms

也许这是 Intel SpeedStep 影响结果，或者可能是 Turbo Boost。无论如何，这都是非常烦人的。

csc 3.5, /platform:x64, runtime v2.0.50727 (via .config)
DynamicMethod: 428 ms
Lambda: 392 ms
Method: 392 ms
Expression: 428 ms

csc 3.5, /platform:x64, runtime v4
DynamicMethod: 428 ms
Lambda: 356 ms
Method: 356 ms
Expression: 428 ms

csc 4, /platform:x64, runtime v4
DynamicMethod: 428 ms
Lambda: 356 ms
Method: 356 ms
Expression: 428 ms

csc 4, /platform:x86, runtime v4
DynamicMethod: 463 ms
Lambda: 570 ms
Method: 570 ms
Expression: 463 ms

csc 3.5, /platform:x86, runtime v4
DynamicMethod: 214 ms
Lambda: 570 ms
Method: 571 ms
Expression: 249 ms

其中许多结果都是时序意外，无论是什么导致了 C# 3.5/运行时 v2.0 场景中的随机加速。我必须重新启动才能查看 SpeedStep 或 Turbo Boost 是否造成了这些影响。

The method created via DynamicMethod goes through two thunks, while the method created via Expression<> doesn't go through any.

Here's how it works. Here's the calling sequence for invoking fn(0, 1) in the Time method (I hard-coded the arguments to 0 and 1 for ease of debugging):

00cc032c 6a01            push    1           // 1 argument
00cc032e 8bcf            mov     ecx,edi
00cc0330 33d2            xor     edx,edx     // 0 argument
00cc0332 8b410c          mov     eax,dword ptr [ecx+0Ch]
00cc0335 8b4904          mov     ecx,dword ptr [ecx+4]
00cc0338 ffd0            call    eax // 1 arg on stack, two in edx, ecx

For the first invocation I investigated, DynamicMethod, the call eax line comes up like so:

00cc0338 ffd0            call    eax {003c2084}
0:000> !u 003c2084
Unmanaged code
003c2084 51              push    ecx
003c2085 8bca            mov     ecx,edx
003c2087 8b542408        mov     edx,dword ptr [esp+8]
003c208b 8b442404        mov     eax,dword ptr [esp+4]
003c208f 89442408        mov     dword ptr [esp+8],eax
003c2093 58              pop     eax
003c2094 83c404          add     esp,4
003c2097 83c010          add     eax,10h
003c209a ff20            jmp     dword ptr [eax]

This appears to be doing some stack swizzling to rearrange arguments. I speculate that it's owing to the difference between delegates that use the implicit 'this' argument and those that don't.

That jump at the end resolves like so:

003c209a ff20            jmp     dword ptr [eax]      ds:0023:012f7edc=0098c098
0098c098 e963403500      jmp     00ce0100

The remainder of the code at 0098c098 looks like a JIT thunk, whose start got rewritten with a jmp after the JIT. It's only after this jump that we get to real code:

0:000> !u eip
Normal JIT generated code
DynamicClass.TestMethod(Int32, Int32)
Begin 00ce0100, size 5
>>> 00ce0100 03ca            add     ecx,edx
00ce0102 8bc1            mov     eax,ecx
00ce0104 c3              ret

The invocation sequence for the method created via Expression<> is different - it's missing the stack swizzling code. Here it is, from the first jump via eax:

00cc0338 ffd0            call    eax {00ce00a8}

0:000> !u eip
Normal JIT generated code
DynamicClass.lambda_method(System.Runtime.CompilerServices.ExecutionScope, Int32, Int32)
Begin 00ce00a8, size b
>>> 00ce00a8 8b442404        mov     eax,dword ptr [esp+4]
00ce00ac 03d0            add     edx,eax
00ce00ae 8bc2            mov     eax,edx
00ce00b0 c20400          ret     4

Now, how did things get like this?

  1. Stack swizzling wasn't necessary (the implicit first argument from the delegate is actually used, i.e. not like a delegate bound to a static method)
  2. The JIT must have been forced by LINQ compilation logic so that the delegate held the real destination address rather than a fake one.

I don't know how the LINQ forced the JIT, but I do know how to force a JIT myself - by calling the function at least once. UPDATE: I found another way to force a JIT: use the restrictedSkipVisibility argumetn to the constructor and pass true. So, here's modified code that eliminates stack swizzling by using the implicit 'this' parameter, and uses the alternate constructor to pre-compile so that the bound address is the real address, rather than the thunk:

using System;
using System.Linq.Expressions;
using System.Reflection.Emit;
using System.Diagnostics;

namespace Sandbox
{
    public class Program
    {
        public static void Main(String[] args)
        {
            DynamicMethod method = new DynamicMethod("TestMethod",
                typeof(Int32), new Type[] { typeof(object), typeof(Int32),
                typeof(Int32) }, true);
            var il = method.GetILGenerator();

            il.Emit(OpCodes.Ldarg_1);
            il.Emit(OpCodes.Ldarg_2);
            il.Emit(OpCodes.Add);
            il.Emit(OpCodes.Ret);

            Func<Int32, Int32, Int32> f1 =
                (Func<Int32, Int32, Int32>)method.CreateDelegate(
                    typeof(Func<Int32, Int32, Int32>), null);
            Func<Int32, Int32, Int32> f2 = (Int32 a, Int32 b) => a + b;
            Func<Int32, Int32, Int32> f3 = Sum;
            Expression<Func<Int32, Int32, Int32>> f4x = (a, b) => a + b;
            Func<Int32, Int32, Int32> f4 = f4x.Compile();
            for (Int32 pass = 1; pass <= 2; pass++)
            {
                // Pass 1 just runs all the code without writing out anything
                // to avoid JIT overhead influencing the results
                Time(f1, "DynamicMethod", pass);
                Time(f2, "Lambda", pass);
                Time(f3, "Method", pass);
                Time(f4, "Expression", pass);
            }
        }

        private static void Time(Func<Int32, Int32, Int32> fn,
            String name, Int32 pass)
        {
            Stopwatch sw = new Stopwatch();
            sw.Start();
            for (Int32 index = 0; index <= 100000000; index++)
            {
                Int32 result = fn(index, 1);
            }
            sw.Stop();
            if (pass == 2)
                Console.WriteLine(name + ": " + sw.ElapsedMilliseconds + " ms");
        }

        private static Int32 Sum(Int32 a, Int32 b)
        {
            return a + b;
        }
    }
}

Here's the runtimes on my system:

DynamicMethod: 312 ms
Lambda: 417 ms
Method: 417 ms
Expression: 312 ms

UPDATED TO ADD:

I tried running this code on my new system, which is an Core i7 920 running Windows 7 x64 with .NET 4 beta 2 installed (mscoree.dll ver. 4.0.30902), and the results are, well, variable.

csc 3.5, /platform:x86, runtime v2.0.50727 (via .config)

Run #1
DynamicMethod: 214 ms
Lambda: 571 ms
Method: 570 ms
Expression: 249 ms

Run #2
DynamicMethod: 463 ms
Lambda: 392 ms
Method: 392 ms
Expression: 463 ms

Run #3
DynamicMethod: 463 ms
Lambda: 570 ms
Method: 570 ms
Expression: 463 ms

Perhaps this is Intel SpeedStep affecting results, or possibly Turbo Boost. In any case, it's very annoying.

csc 3.5, /platform:x64, runtime v2.0.50727 (via .config)
DynamicMethod: 428 ms
Lambda: 392 ms
Method: 392 ms
Expression: 428 ms

csc 3.5, /platform:x64, runtime v4
DynamicMethod: 428 ms
Lambda: 356 ms
Method: 356 ms
Expression: 428 ms

csc 4, /platform:x64, runtime v4
DynamicMethod: 428 ms
Lambda: 356 ms
Method: 356 ms
Expression: 428 ms

csc 4, /platform:x86, runtime v4
DynamicMethod: 463 ms
Lambda: 570 ms
Method: 570 ms
Expression: 463 ms

csc 3.5, /platform:x86, runtime v4
DynamicMethod: 214 ms
Lambda: 570 ms
Method: 571 ms
Expression: 249 ms

Many of these results will be accidents of timing, whatever it is that is causing the random speedups in the C# 3.5 / runtime v2.0 scenario. I'll have to reboot to see if SpeedStep or Turbo Boost is responsible for these effects.

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