starpu-max/doc/vector_scal_c.texi

/*
 * This example demonstrates how to use StarPU to scale an array by a factor.
 * It shows how to manipulate data with StarPU's data management library.
 *  1- how to declare a piece of data to StarPU (starpu_vector_data_register)
 *  2- how to describe which data are accessed by a task (task->buffers[0])
 *  3- how a kernel can manipulate the data (buffers[0].vector.ptr)
 */
#include <starpu.h>
#include <starpu_opencl.h>

#define    NX    2048

extern void scal_cpu_func(void *buffers[], void *_args);
extern void scal_cuda_func(void *buffers[], void *_args);
extern void scal_opencl_func(void *buffers[], void *_args);

static starpu_codelet cl = @{
    .where = STARPU_CPU | STARPU_CUDA | STARPU_OPENCL,
    /* CPU implementation of the codelet */
    .cpu_func = scal_cpu_func,
#ifdef STARPU_USE_CUDA
    /* CUDA implementation of the codelet */
    .cuda_func = scal_cuda_func,
#endif
#ifdef STARPU_USE_OPENCL
    /* OpenCL implementation of the codelet */
    .opencl_func = scal_opencl_func,
#endif
    .nbuffers = 1
@};

#ifdef STARPU_USE_OPENCL
struct starpu_opencl_program programs;
#endif

int main(int argc, char **argv)
@{
    /* We consider a vector of float that is initialized just as any of C
      * data */
    float vector[NX];
    unsigned i;
    for (i = 0; i < NX; i++)
        vector[i] = 1.0f;

    fprintf(stderr, "BEFORE : First element was %f\n", vector[0]);

    /* Initialize StarPU with default configuration */
    starpu_init(NULL);

#ifdef STARPU_USE_OPENCL
        starpu_opencl_load_opencl_from_file(
               "examples/basic_examples/vector_scal_opencl_kernel.cl", &programs);
#endif

    /* Tell StaPU to associate the "vector" vector with the "vector_handle"
     * identifier. When a task needs to access a piece of data, it should
     * refer to the handle that is associated to it.
     * In the case of the "vector" data interface:
     *  - the first argument of the registration method is a pointer to the
     *    handle that should describe the data
     *  - the second argument is the memory node where the data (ie. "vector")
     *    resides initially: 0 stands for an address in main memory, as
     *    opposed to an adress on a GPU for instance.
     *  - the third argument is the adress of the vector in RAM
     *  - the fourth argument is the number of elements in the vector
     *  - the fifth argument is the size of each element.
     */
    starpu_data_handle vector_handle;
    starpu_vector_data_register(&vector_handle, 0, (uintptr_t)vector,
                                NX, sizeof(vector[0]));

    float factor = 3.14;

    /* create a synchronous task: any call to starpu_task_submit will block
      * until it is terminated */
    struct starpu_task *task = starpu_task_create();
    task->synchronous = 1;

    task->cl = &cl;

    /* the codelet manipulates one buffer in RW mode */
    task->buffers[0].handle = vector_handle;
    task->buffers[0].mode = STARPU_RW;

    /* an argument is passed to the codelet, beware that this is a
     * READ-ONLY buffer and that the codelet may be given a pointer to a
     * COPY of the argument */
    task->cl_arg = &factor;
    task->cl_arg_size = sizeof(factor);

    /* execute the task on any eligible computational ressource */
    starpu_task_submit(task);

    /* StarPU does not need to manipulate the array anymore so we can stop
      * monitoring it */
    starpu_data_unregister(vector_handle);

#ifdef STARPU_USE_OPENCL
    starpu_opencl_unload_opencl(&programs);
#endif

    /* terminate StarPU, no task can be submitted after */
    starpu_shutdown();

    fprintf(stderr, "AFTER First element is %f\n", vector[0]);

    return 0;
@}