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[], const char *filename)
{
if(pDst == NULL || filename == NULL)
return ; int size = readlink("/proc/self/exe", pDst, );
while(pDst[size - ] != '/')
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 platforms
cl_int status = clGetPlatformIDs(, NULL, &numPlatforms);
if (status != CL_SUCCESS)
{
puts("Error: Getting platforms!");
return ;
} cl_platform_id platforms[]; /*For clarity, choose the first available platform. */
if(numPlatforms > )
{
status = clGetPlatformIDs(numPlatforms, platforms, NULL);
if(status != CL_SUCCESS)
{
puts("Failed to get platform IDs");
return ;
}
} /*Step 2:Query the platform and choose the first GPU device if has one.Otherwise use the CPU as device.*/
cl_uint numDevices = ;
cl_device_id devices[];
clGetDeviceIDs(platforms[], CL_DEVICE_TYPE_GPU, , NULL, &numDevices);
if(numDevices == ) //no GPU available.
{
puts("No devices available!");
return ;
}
else
{
printf("The number of available devices is: %u\n", numDevices);
clGetDeviceIDs(platforms[], CL_DEVICE_TYPE_GPU, numDevices, devices, NULL);
} /*Step 3: Create context.*/
cl_context context = clCreateContext(NULL,, devices,NULL,NULL,NULL); /*Step 4: Creating command queue associate with the context.*/
cl_command_queue commandQueue = clCreateCommandQueue(context, devices[], , NULL); /*Step 5: Create program object */
char filePath[];
GetCurrentLocationFilePath(filePath, "test.cl");
FILE *fp = fopen(filePath, "r");
if(fp == NULL)
{
puts("OpenCL kernel source file open failed!");
return ;
}
fseek(fp, , SEEK_END);
long fileLength = ftell(fp);
fseek(fp, , SEEK_SET);
char *source = (char*)malloc(fileLength + );
fread(source, , fileLength, fp);
fclose(fp);
size_t sourceSize[] = {fileLength};
cl_program program = clCreateProgramWithSource(context, , (const char**)&source, sourceSize, NULL); free(source);
if(program == NULL)
{
puts("Failed to create the program!");
return ;
} /*Step 6: Build program. */
status = clBuildProgram(program, ,devices,NULL,NULL,NULL);
if(status != CL_SUCCESS)
{
puts("Failed to build the program!");
return ;
} /*Step 7: Initial input,output for the host and create memory objects for the kernel*/
int input[];
for(int i = ; i < ; i++)
input[i] = i + ; 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, , sizeof(cl_mem), &inputBuffer);
status = clSetKernelArg(kernel, , sizeof(cl_mem), &outputBuffer); /*Step 10: Running the kernel.*/
size_t global_work_size[] = { };
status = clEnqueueNDRangeKernel(commandQueue, kernel, , NULL, global_work_size, NULL, , NULL, NULL); /*Step 11: Read the cout put back to host memory.*/
int output[];
status = clEnqueueReadBuffer(commandQueue, outputBuffer, CL_TRUE, , sizeof(input), output, , 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 = ; i < ; i++)
{
if(output[i] != i + )
{
printf("Error occurred @%d!", i);
return ;
}
} puts("Pass!");
return ;
}
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();
out[index] = in[index] + ;
}
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。