OpenCL 三种内存对象的使用

▶ 包括带有 CL_MEM_READ_ONLY，CL_MEM_WRITE_ONLY，CL_MEM_READ_WRITE 标识的显示拷贝（函数 clEnqueueWriteBuffer 和 clEnqueueReadBuffer）；带有 CL_MEM_COPY_HOST_PTR 标识的隐式拷贝（不用拷贝函数，在设备上直接使用）；以及使用函数 clEnqueueMapBuffer 直接在设备和主机之间映射（转换）一段内存的指针

● 代码

 1 #include <cl.h>
 2 #include <stdio.h>
 3 #include <stdlib.h>
 4 #include <time.h>
 5 #include <iostream>
 6 
 7 using namespace std;
 8 const int nElement = 2048;
 9 
10 const char *programSource = "                                              
11 __kernel void vectorAdd(__global int *A, __global int *B, __global int *C) 
12 {                                                                          
13     int idx = get_global_id(0);                                            
14     C[idx] = A[idx] + B[idx];                                              
15     return;                                                                
16 }                                                                          
17 ";
18 
19 int main(int argc, char* argv[])
20 {
21     const size_t dataSize = sizeof(int) * nElement;
22     int i, *A, *B, *C, *returnC;
23 
24     A = (int *)malloc(dataSize);
25     B = (int *)malloc(dataSize);
26     C = (int *)malloc(dataSize);
27     for (srand((unsigned)time(NULL)), i = 0; i < nElement; A[i] = rand() % 65535, B[i] = rand() % 65535, C[i] = A[i] + B[i], i++);
28 
29     cl_int status;
30     cl_platform_id platform;
31     clGetPlatformIDs(1, &platform, NULL);
32     cl_device_id device;
33     clGetDeviceIDs(platform, CL_DEVICE_TYPE_ALL, 1, &device, NULL);
34     cl_context context = clCreateContext(NULL, 1, &device, NULL, NULL, &status);
35     cl_command_queue queue = clCreateCommandQueue(context, device, 0, &status);
36     cl_program program = clCreateProgramWithSource(context, 1, &programSource, NULL, &status);
37     clBuildProgram(program, 1, &device, NULL, NULL, NULL);
38     cl_kernel kernel = clCreateKernel(program, "vectorAdd", NULL);
39     cl_event writeEvent, runEvent, mapEvent;
40 
41     //创建三个内存对象，把 A 隐式拷贝到 clA，把 B 显示拷贝到 clB，clC 接收计算结果映射给 returnC
42     cl_mem clA = clCreateBuffer(context, CL_MEM_READ_ONLY | CL_MEM_COPY_HOST_PTR, dataSize, A, NULL);
43     cl_mem clB = clCreateBuffer(context, CL_MEM_READ_ONLY, dataSize, NULL, NULL);
44     cl_mem clC = clCreateBuffer(context, CL_MEM_WRITE_ONLY, dataSize, NULL, NULL);
45 
46     clEnqueueWriteBuffer(queue, clB, 1, 0, dataSize, B, 0, 0, &writeEvent);
47 
48     clFlush(queue);// 出现需要等待的事件之前，把队列中的任务全部提交掉    
49     clWaitForEvents(1, &writeEvent);// 等待指定事件完成
50 
51                                     // 执行内核
52     size_t global_work_size = nElement;
53     clSetKernelArg(kernel, 0, sizeof(cl_mem), (void*)&clA);
54     clSetKernelArg(kernel, 1, sizeof(cl_mem), (void*)&clB);
55     clSetKernelArg(kernel, 2, sizeof(cl_mem), (void*)&clC);
56     clEnqueueNDRangeKernel(queue, kernel, 1, NULL, &global_work_size, NULL, 0, NULL, &runEvent);
57     clFlush(queue);
58     clWaitForEvents(1, &runEvent);
59 
60     // 结果拷回
61     returnC = (cl_int *)clEnqueueMapBuffer(queue, clC, CL_TRUE, CL_MAP_READ, 0, dataSize, 0, NULL, &mapEvent, NULL);
62     clFlush(queue);
63     clWaitForEvents(1, &mapEvent);
64 
65     //结果验证
66     printf("Verify %s.
", !memcmp(C, returnC, dataSize) ? "passed" : "failed");// 定义在 iostream
67 
68     free(C);
69     free(A);
70     free(B);
71     clReleaseMemObject(clA);
72     clReleaseMemObject(clB);
73     clReleaseMemObject(clC);
74     clReleaseContext(context);
75     clReleaseCommandQueue(queue);
76     clReleaseProgram(program);
77     clReleaseEvent(writeEvent);
78     clReleaseEvent(runEvent);
79     clReleaseEvent(mapEvent);
80     getchar();
81     return 0;
82 }

● 输出结果

Verify passed.

● 注意

■ 事件在声明以后一定要通过某个函数的  cl_event * /* event */  参数定义它，才能进行 clWaitForEvents 或 clReleaseEvent，否则会报错

● 使用 CL_MEM_COPY_HOST_PTR 和 CL_MEM_USE_HOST_PTR 的区别，前者创建一个独立的缓冲区，只是使用了 host_ptr 的值来初始化，后续使用过程中主机端对 host_ptr 的修改不会影响到缓冲区的内容；后者直接使用 host_ptr （转化为设备指针来使用），后续使用过程中主机端对 host_ptr 的修改仍会影响缓冲区内容

● 代码

 1 #include <cl.h>
 2 #include <stdio.h>
 3 #include <stdlib.h>
 4 
 5 using namespace std;
 6 const int nElement = 2048;
 7 
 8 const char *programSource = "               
 9 __kernel void vectorAdd(__global int *A)    
10 {                                           
11     return;                                 
12 }                                           
13 ";
14 
15 int main(int argc, char* argv[])
16 {   
17     const size_t dataSize = sizeof(int) * nElement;
18     int i, sum, *A, *returnA, *mapReturnA;
19             
20     A = (int *)malloc(dataSize);        
21     returnA = (int *)malloc(dataSize);
22     //mapReturnA = (int *)malloc(dataSize);// 注意用作内存映射的指针不需要申请内存，使用这个表达式会造成结尾处的运行时错误
23     for (i = 0; i < nElement; A[i++] = 1);
24 
25     cl_int status;
26     cl_platform_id platform;
27     clGetPlatformIDs(1, &platform, NULL);
28     cl_device_id device;
29     clGetDeviceIDs(platform, CL_DEVICE_TYPE_ALL, 1, &device, NULL);
30     cl_context context = clCreateContext(NULL, 1, &device, NULL, NULL, &status);
31     cl_command_queue queue = clCreateCommandQueue(context, device, 0, &status);
32     cl_program program = clCreateProgramWithSource(context, 1, &programSource, NULL, &status);
33     status = clBuildProgram(program, 1, &device, NULL, NULL, NULL);
34     cl_kernel kernel = clCreateKernel(program, "vectorAdd", &status);
35     
36     cl_mem clA = clCreateBuffer(context, CL_MEM_READ_WRITE | CL_MEM_COPY_HOST_PTR, dataSize, A, NULL);
37     //cl_mem clA = clCreateBuffer(context, CL_MEM_READ_WRITE | CL_MEM_USE_HOST_PTR, dataSize, A, NULL);
38     
39     for (i = 0; i < nElement; A[i++]++);// 在创建缓冲区以后再修改 A 的值
40         
41     size_t global_work_size = nElement; 
42     clSetKernelArg(kernel, 0, sizeof(cl_mem), (void*)&clA);
43     clEnqueueNDRangeKernel(queue, kernel, 1, NULL, &global_work_size, NULL, 0, NULL, NULL);    
44     
45     clEnqueueReadBuffer(queue, clA, CL_TRUE, 0, dataSize, returnA, 0, NULL, NULL);
46     mapReturnA = (cl_int *)clEnqueueMapBuffer(queue, clA, CL_TRUE, CL_MAP_READ, 0, dataSize, 0, NULL, NULL, &status);   
47 
48     for (i = sum = 0; i < nElement; sum += A[i++]);
49     printf("sum A = %d
", sum);
50     for (i = sum = 0; i < nElement; sum += returnA[i++]);
51     printf("sum returnA = %d
", sum);
52     for (i = sum = 0; i < nElement; sum += mapReturnA[i++]);
53     printf("sum mapReturnA = %d
", sum);
54 
55     free(A);    
56     free(returnA);        
57     clReleaseMemObject(clA);    
58     clReleaseContext(context);
59     clReleaseCommandQueue(queue);
60     clReleaseProgram(program);
61     getchar();
62     return 0;
63 }

● 输出结果

■ 使用 CL_MEM_COPY_HOST_PTR，仅有主机端的值被修改

sum A = 4096
sum returnA = 2048
sum mapReturnA = 2048

■ 使用 CL_MEM_USE_HOST_PTR，设备端使用的缓冲区也遭到了修改

sum A = 4096
sum returnA = 4096
sum mapReturnA = 4096
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原文地址：https://www.cnblogs.com/cuancuancuanhao/p/8964534.html