对于Ubuntu或其近亲（Lubuntu、Kubuntu、Mint等）编写OpenCL程序也不会太难。由于本例用的是AMD APP SDK，因此需要AMD的GPU以及相关驱动。首先，去AMD官网下载GPU驱动——AMD Catalyst。如果你用的是APU并且还有一块独立显卡的话，通过AMD Catalyst Control Center可以选择使用哪个GPU。像我现在用的联想Z475笔记本，搭载了AMD APU A6-3420M以及一块AMD Radeon HD 7400M，但是相比较而言，还是APU自带的6620G的GPU性能更強一些，因此我这边设置的是采用AMD Radeon HD 6620G。
在Linux下，AMD官方的GPU驱动是.run文件，只需使用sudo sh xxx.run即可安装。安装时采用默认安装即可。
然后去developer.amd.com开发者网站下载AMD APP SDK。下载完成之后，将lib里面的动态库文件（xxx.so）取出来，并且把include里的头文件取出来。在你的OpenCL工程中把头文件的路径以及动态加载库都设置好。在你用-l的时候，如果动态库文件后缀名为.so.1，那么得把文件名后缀.1去掉。因为-l只能连接.a、.lib、.so等这些后缀的库文件。
下面我们将举一个最简单的例子，首先看主机端代码：
/* ============================================================================ Name : OpenCLTest.c Author : Zenny Chen Version : Copyright : Your copyright notice Description : Hello World in C, Ansi-style ============================================================================ */ #include <stdio.h> #include <string.h> #include <stdlib.h> #include <unistd.h> #include <CL/cl.h> static int GetCurrentLocationFilePath(char pDst[512], const char *filename) { if(pDst == NULL || filename == NULL) return 0; int size = readlink("/proc/self/exe", pDst, 512); while(pDst[size - 1] != '/') size--; strcpy(&pDst[size], filename); int retSize = strlen(filename) + size; pDst[retSize] = ' '; return retSize; } int main(void) { /*Step1: Getting platforms and choose an available one.*/ cl_uint numPlatforms; //the NO. of platforms cl_int status = clGetPlatformIDs(0, NULL, &numPlatforms); if (status != CL_SUCCESS) { puts("Error: Getting platforms!"); return 0; } cl_platform_id platforms[16]; /*For clarity, choose the first available platform. */ if(numPlatforms > 0) { status = clGetPlatformIDs(numPlatforms, platforms, NULL); if(status != CL_SUCCESS) { puts("Failed to get platform IDs"); return 0; } } /*Step 2:Query the platform and choose the first GPU device if has one.Otherwise use the CPU as device.*/ cl_uint numDevices = 0; cl_device_id devices[16]; clGetDeviceIDs(platforms[0], CL_DEVICE_TYPE_GPU, 0, NULL, &numDevices); if(numDevices == 0) //no GPU available. { puts("No devices available!"); return 0; } else { printf("The number of available devices is: %u ", numDevices); clGetDeviceIDs(platforms[0], CL_DEVICE_TYPE_GPU, numDevices, devices, NULL); } /*Step 3: Create context.*/ cl_context context = clCreateContext(NULL,1, devices,NULL,NULL,NULL); /*Step 4: Creating command queue associate with the context.*/ cl_command_queue commandQueue = clCreateCommandQueue(context, devices[0], 0, NULL); /*Step 5: Create program object */ char filePath[512]; GetCurrentLocationFilePath(filePath, "test.cl"); FILE *fp = fopen(filePath, "r"); if(fp == NULL) { puts("OpenCL kernel source file open failed!"); return 0; } fseek(fp, 0, SEEK_END); long fileLength = ftell(fp); fseek(fp, 0, SEEK_SET); char *source = (char*)malloc(fileLength + 1); fread(source, 1, fileLength, fp); fclose(fp); size_t sourceSize[] = {fileLength}; cl_program program = clCreateProgramWithSource(context, 1, (const char**)&source, sourceSize, NULL); free(source); if(program == NULL) { puts("Failed to create the program!"); return 0; } /*Step 6: Build program. */ status = clBuildProgram(program, 1,devices,NULL,NULL,NULL); if(status != CL_SUCCESS) { puts("Failed to build the program!"); return 0; } /*Step 7: Initial input,output for the host and create memory objects for the kernel*/ int input[128]; for(int i = 0; i < 128; i++) input[i] = i + 1; cl_mem inputBuffer = clCreateBuffer(context, CL_MEM_READ_ONLY|CL_MEM_COPY_HOST_PTR, sizeof(input), input, NULL); cl_mem outputBuffer = clCreateBuffer(context, CL_MEM_WRITE_ONLY , sizeof(input), NULL, NULL); /*Step 8: Create kernel object */ cl_kernel kernel = clCreateKernel(program, "test", NULL); /*Step 9: Sets Kernel arguments.*/ status = clSetKernelArg(kernel, 0, sizeof(cl_mem), &inputBuffer); status = clSetKernelArg(kernel, 1, sizeof(cl_mem), &outputBuffer); /*Step 10: Running the kernel.*/ size_t global_work_size[1] = { 128 }; status = clEnqueueNDRangeKernel(commandQueue, kernel, 1, NULL, global_work_size, NULL, 0, NULL, NULL); /*Step 11: Read the cout put back to host memory.*/ int output[128]; status = clEnqueueReadBuffer(commandQueue, outputBuffer, CL_TRUE, 0, sizeof(input), output, 0, NULL, NULL); /*Step 12: Clean the resources.*/ status = clReleaseKernel(kernel); //Release kernel. status = clReleaseProgram(program); //Release the program object. status = clReleaseMemObject(inputBuffer); //Release mem object. status = clReleaseMemObject(outputBuffer); status = clReleaseCommandQueue(commandQueue); //Release Command queue. status = clReleaseContext(context); //Release context. for(int i = 0; i < 128; i++) { if(output[i] != i + 2) { printf("Error occurred @%d!", i); return 0; } } puts("Pass!"); return 1; }
在编译选项中，使用-std=gnu99或-std=gnu11。上述代码为纯C语言，因此即便你没有安装g++也完全没关系。
下面看看内核源代码：
/* ============================================================================ Name : OpenCLTest.c Author : Zenny Chen Version : Copyright : Your copyright notice Description : Simple OpenCL kernel source ============================================================================ */ __kernel void test(__global int* in, __global int* out) { int index = get_global_id(0); out[index] = in[index] + 1; }
将此文件放在可执行文件相同路径下，然后我们就能正常运行了。