OpenACC 简单的直方图

▶ 简单的直方图，强调原子操作的使用

● 代码

 #include <stdio.h>
 #include <stdlib.h>
 #include <openacc.h>

 int main()
 {
     const int length = , basket = ;
     int data[length], histgram[basket];

     srand();
     for (int i = ; i < basket; histgram[i++] = );
     for (int i = ; i < length; data[i++] = rand() % );

 #pragma acc parallel loop
     for (int i = ; i < length; i++)
     {
 #pragma acc atomic update
         histgram[data[i]]+=;
     }

     for (int i = ; i < basket; i++)
         printf("histgram[%d] = %d\n", i, histgram[i]);

     getchar();
     return ;
 }

● 输出结果，在 Windows 里是错的，在 WSL 里是对的

D:\Code\OpenACC\OpenACCProject\OpenACCProject>pgcc -acc -Minfo main.c -o main_acc.exe
main:
     , Accelerator kernel generated
         Generating Tesla code
         , #pragma acc loop gang, vector(128) /* blockIdx.x threadIdx.x */
     , Generating implicit copyout(histgram[data])
         Generating implicit copyin(data[:])

D:\Code\OpenACC\OpenACCProject\OpenACCProject>main_acc.exe
launch CUDA kernel  file=D:\Code\OpenACC\OpenACCProject\OpenACCProject\main.c function=main line= device= threadid= num_gangs= num_workers= vector_length= grid= block=
histgram[] =
histgram[] =
histgram[] =
histgram[] =
histgram[] =
histgram[] =
histgram[] =
histgram[] =
histgram[] =
histgram[] = 

cuan@CUAN:/mnt/d/Code/OpenACC/OpenACCProject/OpenACCProject$ pgcc -acc -Minfo main.c -o main_acc_ubuntu.exe
main:
     , Accelerator kernel generated
         Generating Tesla code
         , #pragma acc loop gang, vector(128) /* blockIdx.x threadIdx.x */
     , Generating implicit copyout(histgram[data])
         Generating implicit copyin(data[:])
cuan@CUAN:/mnt/d/Code/OpenACC/OpenACCProject/OpenACCProject$ ./main_acc_ubuntu.exe
histgram[] =
histgram[] =
histgram[] =
histgram[] =
histgram[] =
histgram[] =
histgram[] =
histgram[] =
histgram[] =
histgram[] = 

● 添加一个重甲你变量用来存储 data[i]，在 Windos 下也正确了

 #include <stdio.h>
 #include <stdlib.h>
 #include <openacc.h>

 int main()
 {
     const int length = , basket = ;
     int data[length], histgram[basket];

     srand();
     for (int i = ; i < basket; histgram[i++] = );
     for (int i = ; i < length; data[i++] = rand() % );

     int temp;               // 新定义一个变量
 #pragma acc parallel loop
     for (int i = ; i < length; i++)
     {
         temp = data[i];     // 原子操作之前先单独计算下标
 #pragma acc atomic update
         histgram[temp] += ;// 使用 temp 作为下标
     }

     for (int i = ; i < basket; i++)
         printf("histgram[%d] = %d\n", i, histgram[i]);

     getchar();
     return ;
 }