CUDA学习3 Max pooling （python c++ cuda）

1.Python

在CNN4 参数优化中有一个CNN模型，其中的限速步是max pooling。

如下所示，Python中运行一个50*100*24*24的max pooling需要3秒。

import numpy as np
import time

def simple_pool(input, ds=(2, 2)):
    n, m, h, w = input.shape
    d, s = ds
    zh = h / d + h % d
    zw = w / s + w % s
    z = np.zeros((n, m,zh,zw))
    for k in range(n):
        for o in range(m):
            for i in range(zh):
                for j in range(zw):
                    maxd = -10000
                    for u in range(min(d,h-d*i) ):
                        for v in range(min(d,w-d*j)):
                            if input[k,o,d*i+u,d*j+v]>maxd:
                                maxd=input[k,o,d*i+u,d*j+v]
                    z[k, o, i, j] = maxd

    return z

N,M,H,W=[50,100,24,24]
a=np.reshape(range(N*M*H*W),(N,M,H,W))*0.01
start_time= time.time()
out_data=simple_pool(a)
print "Cost:",time.time()-start_time,"s"
print out_data[0,0,0,:10]

"""
Cost: 3.08899998665 s
[ 0.25  0.27  0.29  0.31  0.33  0.35  0.37  0.39  0.41  0.43]
"""

2.C++

采用c++，仅需16~30ms。

#include<iostream>
#include<windows.h>

void MaxPool2d(const float* const bottom_data, const int num, const int channels,
    const int height, const int width, const int pooled_height,float* top_data)
{
    const int w = width;
    const int h = height;
    const int m = channels;
    const int n = num;
    const int d = pooled_height;
    const int zh = h / d + h % d;
    const int zw = w / d + w % d;
    int i,j,k,o,u,v,index,index2=0;
    float s;
    for (k = 0; k < n; ++k)
        for (o = 0; o < m; ++o)
            for (i = 0; i < zh; ++i)
                for (j = 0; j < zw; ++j)
                {
                    index=k*m*h*w+o*h*w+d*i*w+d*j;
                    s=-10000.0;
                    for (u = 0; u < d&&(u+d*i)<h; ++u)
                        for (v = 0; v < d&&(v+d*j)<w; ++v)
                            if (*(bottom_data+index+u*w+v)>s)
                                s=*(bottom_data+index+u*w+v);
                    *(top_data+index2)=s;
                    ++index2;
                }
}

int main()
{
  const int N=50,M=100,H=24,W=24,P=(H+1)/2;
  float mul_min=0.01;
  float *input,*output;
  input=new float [N*M*H*W*sizeof(float)];
  output=new float [N*M*P*P*sizeof(float)];
  for(int i=0;i<N*M*H*W;i++)
    *(input+i)=i*mul_min;

  DWORD start_time=GetTickCount();
  MaxPool2d(input,N,M,H,W,2,output);
  DWORD end_time=GetTickCount();
  std::cout<<"Cost: "<<end_time-start_time<<"ms."<<std::endl;
  for(int i=0;i<10;i++)
    std::cout<<*(output+i)<<std::endl;

  delete []input;
  delete []output;
}

/*
Cost: 16ms.
0.25
0.27
0.29
0.31
0.33
0.35
0.37
0.39
0.41
0.43
*/

3.CUDA

在N=50时为16ms，N=500时为141ms（c++中为218ms），略有提升，应该是计算快了一些，数据交换慢了一些。

#include <windows.h>
#include <iostream>

__global__ void MaxPool2d(float* bottom_data, const int height, const int width, 
    const int pooled_height,const int out_height,float* top_data)
{
    int x = blockIdx.x;
    int y = blockIdx.y;
    int i,j,u,v,index;
    int index2=x*gridDim.y*out_height*out_height+y*out_height*out_height;
    float s;
    for (i = 0; i < out_height; ++i)
        for (j = 0; j < out_height; ++j)
        {
            index=x*gridDim.y*height*width+y*height*width+i*pooled_height*width+j*pooled_height;
            s=-10000.0;
            for (u = 0; u < pooled_height&&(u+pooled_height*i)<height; ++u)
                for (v = 0; v < pooled_height&&(v+pooled_height*j)<width; ++v)
                    if (*(bottom_data+index+u*width+v)>s)
                        s=*(bottom_data+index+u*width+v);
            *(top_data+index2)=s;
            ++index2;
        }
}

int main()
{
  const int N=500,M=100,H=24,W=24,D=2;
  const int PH=H / D + H % D;
  int image_size = N*M*H*W*sizeof(float);
  int out_size = N*M*PH*PH*sizeof(float);
  float mul_by=0.01;
  float *input,*output,*dev_output,*dev_input;
  input = new float[image_size];
  output = new float[out_size];
  for (int i = 0; i<N*M*H*W; i++)
      *(input + i) = i*mul_by;

  cudaMalloc((void**)&dev_output, out_size);
  cudaMalloc((void**)&dev_input, image_size);
  cudaMemcpy(dev_input, input, image_size, cudaMemcpyHostToDevice);
  dim3    grid(N, M);
  DWORD start_time=GetTickCount();
  MaxPool2d<<<grid,1>>>(dev_input,H,W,D,PH,dev_output);
  cudaMemcpy(output, dev_output, out_size, cudaMemcpyDeviceToHost);
  DWORD end_time=GetTickCount();
  std::cout<<"Cost: "<<end_time-start_time<<"ms."<<std::endl;
  for (int i = 0; i<10; i++)
      std::cout << *(output + i) << std::endl;

  cudaFree(dev_input);
  cudaFree(dev_output);
  delete[] output;
  delete[] input;
  system("pause");
}

/*
Cost: 141ms.
0.25
0.27
0.29
0.31
0.33
0.35
0.37
0.39
0.41
0.43
*/