pytorch中使用cuda扩展的实现示例

以下面这个例子作为教程，实现功能是element-wise add；

（pytorch中想调用cuda模块，还是用另外使用C编写接口脚本）

第一步：cuda编程的源文件和头文件

// mathutil_cuda_kernel.cu// 头文件，最后一个是cuda特有的#include <curand.h>#include <stdio.h>#include <math.h>#include <float.h>#include "mathutil_cuda_kernel.h"// 获取GPU线程通道信息dim3 cuda_gridsize(int n){  int k = (n - 1) / BLOCK + 1;  int x = k;  int y = 1;  if(x > 65535) {    x = ceil(sqrt(k));    y = (n - 1) / (x * BLOCK) + 1;  }  dim3 d(x, y, 1);  return d;}// 这个函数是cuda执行函数，可以看到细化到了每一个元素__global__ void broadcast_sum_kernel(float *a, float *b, int x, int y, int size){  int i = (blockIdx.x + blockIdx.y * gridDim.x) * blockDim.x + threadIdx.x;  if(i >= size) return;  int j = i % x; i = i / x;  int k = i % y;  a[IDX2D(j, k, y)] += b[k];}// 这个函数是与c语言函数链接的接口函数void broadcast_sum_cuda(float *a, float *b, int x, int y, cudaStream_t stream){  int size = x * y;  cudaError_t err;    // 上面定义的函数  broadcast_sum_kernel<<<cuda_gridsize(size), BLOCK, 0, stream>>>(a, b, x, y, size);  err = cudaGetLastError();  if (cudaSuccess != err)  {    fprintf(stderr, "CUDA kernel failed : %s/n", cudaGetErrorString(err));    exit(-1);  }}

#ifndef _MATHUTIL_CUDA_KERNEL#define _MATHUTIL_CUDA_KERNEL#define IDX2D(i, j, dj) (dj * i + j)#define IDX3D(i, j, k, dj, dk) (IDX2D(IDX2D(i, j, dj), k, dk))#define BLOCK 512#define MAX_STREAMS 512#ifdef __cplusplusextern "C" {#endifvoid broadcast_sum_cuda(float *a, float *b, int x, int y, cudaStream_t stream);#ifdef __cplusplus}#endif#endif

第二步：C编程的源文件和头文件（接口函数）

// mathutil_cuda.c// THC是pytorch底层GPU库#include <THC/THC.h>#include "mathutil_cuda_kernel.h"extern THCState *state;int broadcast_sum(THCudaTensor *a_tensor, THCudaTensor *b_tensor, int x, int y){  float *a = THCudaTensor_data(state, a_tensor);  float *b = THCudaTensor_data(state, b_tensor);  cudaStream_t stream = THCState_getCurrentStream(state);  // 这里调用之前在cuda中编写的接口函数  broadcast_sum_cuda(a, b, x, y, stream);  return 1;}

int broadcast_sum(THCudaTensor *a_tensor, THCudaTensor *b_tensor, int x, int y);

第三步：编译，先编译cuda模块，再编译接口函数模块（不能放在一起同时编译）

nvcc -c -o mathutil_cuda_kernel.cu.o mathutil_cuda_kernel.cu -x cu -Xcompiler -fPIC -arch=sm_52

import osimport torchfrom torch.utils.ffi import create_extensionthis_file = os.path.dirname(__file__)sources = []headers = []defines = []with_cuda = Falseif torch.cuda.is_available():  print('Including CUDA code.')  sources += ['src/mathutil_cuda.c']  headers += ['src/mathutil_cuda.h']  defines += [('WITH_CUDA', None)]  with_cuda = Truethis_file = os.path.dirname(os.path.realpath(__file__))extra_objects = ['src/mathutil_cuda_kernel.cu.o']  # 这里是编译好后的.o文件位置extra_objects = [os.path.join(this_file, fname) for fname in extra_objects]ffi = create_extension(  '_ext.cuda_util',  headers=headers,  sources=sources,  define_macros=defines,  relative_to=__file__,  with_cuda=with_cuda,  extra_objects=extra_objects)if __name__ == '__main__':  ffi.build()