Ubuntu下使用AMD APP编写OpenCL程序

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.cAuthor      : Zenny ChenVersion     :Copyright   : Your copyright noticeDescription : 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] = '\0';return retSize;
}int main(void)
{/*Step1: Getting platforms and choose an available one.*/cl_uint numPlatforms;   //the NO. of platformscl_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\n", 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.cAuthor      : Zenny ChenVersion     :Copyright   : Your copyright noticeDescription : Simple OpenCL kernel source============================================================================*/__kernel void test(__global int* in, __global int* out)
{int index = get_global_id(0);out[index] = in[index] + 1;
}