First invocation: OpenACC library API

In this second use case (see below), a function in the OpenACC library is called prior to any of the functions in the CUBLAS library. More specificially, the function acc_set_device_num().

In the use case presented here, the function acc_set_device_num() is used to both initialize the OpenACC library and allocate the hardware resources on the host and the device. In the call to the function, the call parameters specify which device to use and what device type to use, i.e., acc_device_nvidia. It should be noted that this is but one method to initialize the OpenACC library and allocate the appropriate hardware resources. Other methods are available through the use of environment variables and these will be discussed in the next section.

Once the call to acc_set_device_num() has completed, other OpenACC functions can be called as seen with multiple calls being made to acc_copyin(). In addition, calls can be made to functions in the CUBLAS library. In the use case a call to cublasCreate() is made subsequent to the calls to acc_copyin(). As seen in the previous use case, a call to cublasCreate() initializes the CUBLAS library and allocates the hardware resources on the host and the device. However, since the device has already been allocated, cublasCreate() will only initialize the CUBLAS library and allocate the appropriate hardware resources on the host. The context that was created as part of the OpenACC initialization is shared with the CUBLAS library, similarly to the first use case.

dev = 0;

acc_set_device_num(dev, acc_device_nvidia);

/* Copy the first set to the device */
d_X = acc_copyin(&h_X[0], N * sizeof (float));
if (d_X == NULL)
{
    fprintf(stderr, "copyin error h_X\n");
    exit(EXIT_FAILURE);
}

/* Copy the second set to the device */
d_Y = acc_copyin(&h_Y1[0], N * sizeof (float));
if (d_Y == NULL)
{
    fprintf(stderr, "copyin error h_Y1\n");
    exit(EXIT_FAILURE);
}

/* Create the handle */
s = cublasCreate(&h);
if (s != CUBLAS_STATUS_SUCCESS)
{
    fprintf(stderr, "cublasCreate failed %d\n", s);
    exit(EXIT_FAILURE);
}

/* Perform saxpy using CUBLAS library function */
s = cublasSaxpy(h, N, &alpha, d_X, 1, d_Y, 1);
if (s != CUBLAS_STATUS_SUCCESS)
{
    fprintf(stderr, "cublasSaxpy failed %d\n", s);
    exit(EXIT_FAILURE);
}

/* Copy the results from the device */
acc_memcpy_from_device(&h_Y1[0], d_Y, N * sizeof (float));