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OpenCL Example


Platform informations​

get_info.cpp
#include <CL/cl.h>
#include <cstdlib>
#include <iostream>

using namespace std;

int main(void) {
    cl_int  status;
    size_t  str_info_size;
    char *  str_info;
    cl_uint uint_info;

    cl_uint         num_platforms;
    cl_platform_id *platforms;

    cl_uint       num_devices;
    cl_device_id *devices;

    status = clGetPlatformIDs(0, NULL, &num_platforms);
    if(status != CL_SUCCESS) {
        cerr << "Failed to get the number of platforms." << endl;
        return -1;
    }

    if(num_platforms > 0) {
        cout << "* The number of platforms: " << num_platforms << endl;
    } else {
        cerr << "The number of platforms is zero." << endl;
        return -1;
    }

    platforms
        = (cl_platform_id *)malloc(sizeof(cl_platform_id) * num_platforms);
    clGetPlatformIDs(num_platforms, platforms, NULL);

    for(int i = 0; i < num_platforms; ++i) {
        cout << "  -----------------------------------------------" << endl;
        cout << "  Platform-" << i + 1 << endl;

        clGetPlatformInfo(
            platforms[i], CL_PLATFORM_NAME, 0, NULL, &str_info_size);
        str_info = (char *)malloc(str_info_size);
        clGetPlatformInfo(
            platforms[i], CL_PLATFORM_NAME, str_info_size, str_info, NULL);
        cout << "  * Platform: " << str_info << endl;
        free(str_info);

        clGetPlatformInfo(
            platforms[i], CL_PLATFORM_PROFILE, 0, NULL, &str_info_size);
        str_info = (char *)malloc(str_info_size);
        clGetPlatformInfo(
            platforms[i], CL_PLATFORM_PROFILE, str_info_size, str_info, NULL);
        cout << "  * Profile: " << str_info << endl;
        free(str_info);

        clGetPlatformInfo(
            platforms[i], CL_PLATFORM_VERSION, 0, NULL, &str_info_size);
        str_info = (char *)malloc(str_info_size);
        clGetPlatformInfo(
            platforms[i], CL_PLATFORM_VERSION, str_info_size, str_info, NULL);
        cout << "  * " << str_info << endl;
        free(str_info);

        status = clGetDeviceIDs(
            platforms[i], CL_DEVICE_TYPE_ALL, 0, NULL, &num_devices);
        if(status != CL_SUCCESS) {
            cerr << "Failed to get the number of devices in the platform "
                 << i + 1 << '.' << endl;
            continue;
        }

        if(num_devices > 0) {
            cout << "  * The number of devices: " << num_devices << endl;
        } else {
            cerr << "Platform-" << i + 1 << " has no devices." << endl;
            continue;
        }

        devices = (cl_device_id *)malloc(sizeof(cl_device_id) * num_devices);
        clGetDeviceIDs(
            platforms[i], CL_DEVICE_TYPE_ALL, num_devices, devices, NULL);

        for(int j = 0; j < num_devices; ++j) {
            cout << "    ================================================="
                 << endl;
            cout << "    Device-" << j + 1 << endl;

            clGetDeviceInfo(
                devices[j], CL_DEVICE_NAME, 0, NULL, &str_info_size);
            str_info = (char *)malloc(str_info_size);
            clGetDeviceInfo(
                devices[j], CL_DEVICE_NAME, str_info_size, str_info, NULL);
            cout << "    * name: " << str_info << endl;
            free(str_info);

            clGetDeviceInfo(devices[j],
                            CL_DEVICE_MAX_COMPUTE_UNITS,
                            sizeof(uint_info),
                            &uint_info,
                            NULL);
            cout << "    * Max Compute Units: " << uint_info << endl;

            clGetDeviceInfo(devices[j],
                            CL_DEVICE_MAX_CLOCK_FREQUENCY,
                            sizeof(uint_info),
                            &uint_info,
                            NULL);
            cout << "    * Max Clock freq: " << uint_info << endl;

            cout << "    ================================================="
                 << endl;
        }
        cout << "  -----------------------------------------------" << endl;
    }

    free(devices);
    free(platforms);
    return 0;
}
g++ -o get_info get_info.cpp -lOpenCL

SAXPY, CPU vs. GPU or Mali-GPU​

saxpy_cpu_vs_gpu.cpp
#include <CL/cl.h>
#include <cstdlib>
#include <cstring>
#include <ctime>
#include <iostream>

using namespace std;

const int LENGTH = 1000000;

const char *source
    = "__kernel void saxpy(const __global float *X, \n"
      "                    __global float *Y,       \n"
      "                    const float a) {         \n"
      "    uint gid = get_global_id(0);             \n"
      "    Y[gid]   = a * X[gid] + Y[gid];          \n"
      "}                                            \n";

int main(void) {
    cout << fixed;

    cl_int status;
    time_t t, t2 = 0;

    cl_uint         num_platforms = 1;
    cl_platform_id *platforms
        = (cl_platform_id *)malloc(sizeof(cl_platform_id) * num_platforms);
    clGetPlatformIDs(num_platforms, platforms, NULL);

    cl_uint       num_devices = 2;
    cl_device_id *devices
        = (cl_device_id *)malloc(sizeof(cl_device_id) * num_devices);
    clGetDeviceIDs(
        platforms[0], CL_DEVICE_TYPE_ALL, num_devices, devices, NULL);

    cl_context context
        = clCreateContext(NULL, 1, &devices[0], NULL, NULL, NULL);

    cl_command_queue queue = clCreateCommandQueue(context, devices[0], 0, NULL);

    cl_program program = clCreateProgramWithSource(
        context, 1, (const char **)&source, NULL, NULL);

    status = clBuildProgram(program, 1, &devices[0], NULL, NULL, NULL);
    if(status != CL_SUCCESS) {
        cerr << "clBuildProgram failed: " << status << endl;
        char log[0x10000];
        clGetProgramBuildInfo(
            program, devices[0], CL_PROGRAM_BUILD_LOG, 0x10000, log, NULL);
        cerr << log << endl;
        return -1;
    }

    cl_kernel kernel = clCreateKernel(program, "saxpy", NULL);

    cl_float *p_x      = (cl_float *)calloc(LENGTH, sizeof(cl_float));
    cl_float *p_y      = (cl_float *)calloc(LENGTH, sizeof(cl_float));
    cl_float *p_ret    = (cl_float *)calloc(LENGTH, sizeof(cl_float));
    cl_float *p_cl_ret = (cl_float *)calloc(LENGTH, sizeof(cl_float));
    cl_float  a        = 2.f;

    srand(time(NULL));
    for(int i = 0; i < LENGTH; ++i) {
        p_x[i] = (cl_float)rand() / RAND_MAX;
        p_y[i] = (cl_float)rand() / RAND_MAX;
    }

    cl_mem buf_x = clCreateBuffer(
        context, CL_MEM_READ_ONLY, sizeof(cl_float) * LENGTH, NULL, NULL);
    cl_mem buf_y = clCreateBuffer(
        context, CL_MEM_READ_WRITE, sizeof(cl_float) * LENGTH, NULL, NULL);

    t = clock();

    for(int i = 0; i < LENGTH; ++i) { p_ret[i] = a * p_x[i] + p_y[i]; }

    t = clock() - t;
    cout << "CPU" << endl;
    cout << "  * Time (s):                              "
         << (double)t / CLOCKS_PER_SEC << endl;
    cout << "---------------------------------------------------" << endl;

    t = clock();

    clEnqueueWriteBuffer(queue,
                         buf_x,
                         CL_TRUE,
                         0,
                         sizeof(cl_float) * LENGTH,
                         p_x,
                         0,
                         NULL,
                         NULL);
    clEnqueueWriteBuffer(queue,
                         buf_y,
                         CL_TRUE,
                         0,
                         sizeof(cl_float) * LENGTH,
                         p_y,
                         0,
                         NULL,
                         NULL);

    clSetKernelArg(kernel, 0, sizeof(cl_mem), &buf_x);
    clSetKernelArg(kernel, 1, sizeof(cl_mem), &buf_y);
    clSetKernelArg(kernel, 2, sizeof(cl_float), &a);

    t = clock() - t;
    t2 += t;
    cout << "GPU" << endl;
    cout << "  * Writes buffers and sets arguments (s): "
         << (double)t / CLOCKS_PER_SEC << endl;

    t = clock();

    clEnqueueNDRangeKernel(
        queue, kernel, 1, NULL, (size_t *)&LENGTH, NULL, 0, NULL, NULL);

    clFinish(queue);

    t = clock() - t;
    t2 += t;
    cout << "  * Runnig a kernel (s):                   "
         << (double)t / CLOCKS_PER_SEC << endl;

    t = clock();

    clEnqueueReadBuffer(queue,
                        buf_y,
                        CL_TRUE,
                        0,
                        sizeof(cl_float) * LENGTH,
                        p_cl_ret,
                        0,
                        NULL,
                        NULL);

    t = clock() - t;
    t2 += t;
    cout << "  * Reads buffer (s):                      "
         << (double)t / CLOCKS_PER_SEC << endl;
    cout << endl
         << "  * Total time (s):                        "
         << (double)t2 / CLOCKS_PER_SEC << endl;

    for(int i = 0; i < LENGTH; ++i) {
        if(abs(p_ret[i] - p_cl_ret[i]) > 0.01) {
            cout << "Failed to SAXPY" << endl;
        }
    }

    clReleaseMemObject(buf_y);
    clReleaseMemObject(buf_x);
    free(p_cl_ret);
    free(p_ret);
    free(p_y);
    free(p_x);
    clReleaseKernel(kernel);
    clReleaseProgram(program);
    clReleaseCommandQueue(queue);
    clReleaseContext(context);
    free(devices);
    free(platforms);

    return 0;
}
g++ -o saxpy_cpu_vs_gpu saxpy_cpu_vs_gpu.cpp -lOpenCL

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