SYCL

SYCL (pronounced ‘sickle’) is a royalty-free, cross-platform abstraction layer that enables code for heterogeneous processors to be written using standard ISO C++ with the host and kernel code for an application contained in the same source file.

• Specification: https://www.khronos.org/sycl/
• Source code of the compiler: https://github.com/intel/llvm
• ALCF Tutorial: https://github.com/argonne-lcf/sycltrain

module load oneapi

Note

This module (compilers, libraries) gets built periodically from the latest open-source rather than releases. For more details on the release version of compiler, please find the details here. As such, these compilers will get new features and updates quickly that may break on occasion. Please submit any issues at the respective github repositories for the compilers and libraries.

Components

• These are the list of components associated with this module

User Application	Component
Compilers	DPC++
oneMKL Interfaces	oneMKL
oneDPL	oneDPL
SYCLomatic/DPCT	dpct

Dependencies

• SYCL programming model is supported through oneapi compilers that were built from source-code
• Loading this module switches the default programming environment to GNU and with the following dependencies
• PrgEnv-gnu
• cudatoolkit-standalone
• Environment variable is set when loading the module: ONEAPI_DEVICE_SELECTOR=ext_oneapi_cuda:gpu

Example (memory intilization)

#include <sycl/sycl.hpp>

int main(){
    const int N= 100;
    sycl::queue Q;
    float *A = sycl::malloc_shared<float>(N, Q);

    std::cout << "Running on "
              << Q.get_device().get_info<sycl::info::device::name>()
              << "\n";

    // Create a command_group to issue command to the group
    Q.parallel_for(N, [=](sycl::item<1> id) { A[id] = 0.1 * id; }).wait();

    for (size_t i = 0; i < N; i++)
        std::cout << "A[ " << i << " ] = " << A[i] << std::endl;
    return 0;
}

Compile and Run

$ clang++ -std=c++17 -sycl-std=2020 -fsycl -fsycl-targets=nvptx64-nvidia-cuda -Xsycl-target-backend --cuda-gpu-arch=sm_80 main.cpp
$ ./a.out

Example (using GPU-aware MPI)

#include <stdlib.h>
#include <stdio.h>
#include <mpi.h>

#include <sycl/sycl.hpp>

// Modified from NERSC website:
// https://docs.nersc.gov/development/programming-models/mpi
int main(int argc, char *argv[]) {

    int myrank, num_ranks;
    double *val_device;
    double *val_host;
    char machine_name[MPI_MAX_PROCESSOR_NAME];
    int name_len=0;

    MPI_Init(&argc, &argv);
    MPI_Comm_rank(MPI_COMM_WORLD, &myrank);
    MPI_Comm_size(MPI_COMM_WORLD, &num_ranks);
    MPI_Get_processor_name(machine_name, &name_len);

    sycl::queue q{sycl::gpu_selector_v};

    std::cout << "Rank #" << myrank << " runs on: " << machine_name
              << ", uses device: "
              << q.get_device().get_info<sycl::info::device::name>() << "\n";

    MPI_Barrier(MPI_COMM_WORLD);
    int one=1;
    val_host = (double *)malloc(one*sizeof(double));
    val_device = sycl::malloc_device<double>(one,q);

    const size_t size_of_double = sizeof(double);
    *val_host = -1.0;
    if (myrank != 0) {
        std::cout << "I am rank " << myrank
                  << " and my initial value is: " << *val_host << "\n";
    }

    if (myrank == 0) {
        *val_host = 42.0;
        q.memcpy(val_device,val_host,size_of_double).wait();
        std::cout << "I am rank " << myrank
                  << " and will broadcast value: " << *val_host << "\n";
    }

    MPI_Bcast(val_device, 1, MPI_DOUBLE, 0, MPI_COMM_WORLD);

    double check = 42.0;
    if (myrank != 0) {
        //Device to Host
        q.memcpy(val_host,val_device,size_of_double).wait();
        assert(*val_host == check);
        std::cout << "I am rank " << myrank
                  << " and received broadcast value: " << *val_host << "\n";
    }

    sycl::free(val_device,q);
    free(val_host);

    MPI_Finalize();

    return 0;
}

Load Modules

module load oneapi
module load mpiwrappers/cray-mpich-oneapi
export MPICH_GPU_SUPPORT_ENABLED=1

Compile and Run

$ mpicxx -L/opt/cray/pe/mpich/8.1.16/gtl/lib -lmpi_gtl_cuda -std=c++17 -fsycl -fsycl-targets=nvptx64-nvidia-cuda -Xsycl-target-backend --cuda-gpu-arch=sm_80 main.cpp
$ mpiexec -n 2 --ppn 2 --depth=1 --cpu-bind depth ./set_affinity_gpu_polaris.sh ./a.out

For further details regarding the arguments passed to mpiexec command shown above, please visit the Job Scheduling and Execution section. A simple example describing the details and execution of the set_affinity_gpu_polaris.sh file can be found here.

Note: By default, there is no GPU-aware MPI library linking support. The example above shows how the user can enable the linking by specifying the path to the GTL (GPU Transport Layer) library (libmpi_gtl_cuda) to the link line.

oneAPI Math Kernel Library (oneMKL) Interfaces

oneMKL Interfaces is an open-source implementation of the oneMKL Data Parallel C++ (DPC++) interface according to the oneMKL specification. It works with multiple devices (backends) using device-specific libraries underneath.

oneMKL is part of oneAPI. Various backend supported are shown below. More Information here.

User Application	Third-Party Library
	cuBLAS
oneMKL interface	cuSOLVER
	cuRAND

Example (using onemkl::gemm)

The following snippet shows how to compile and run a SYCL code with oneMKL library. For instance, a GPU-based GEMM is performed using mkl::gemm API and the results are compared to a CPU-based GEMM performed using the traditional blas (e.g., AOCL-BLIS) library.

#include <limits>
#include <random>

#include <sycl/sycl.hpp>

#include <oneapi/mkl.hpp>  // ONEMKL GPU header
#include <cblas.h>         // BLIS   CPU header

// Matrix size constants
#define SIZE 4800 // Must be a multiple of 8.
#define M SIZE / 8
#define N SIZE / 4
#define P SIZE / 2

//////////////////////////////////////////////////////////////////////////////////////////

bool ValueSame(double a, double b) { return std::fabs(a - b) < 1.0e-08; }
int VerifyResult(double *c_A, double *c_B) {
  bool MismatchFound = false;

  for (size_t i = 0; i < M; i++) {
    for (size_t j = 0; j < P; j++) {
      if (!ValueSame(c_A[i * P + j], c_B[i * P + j])) {
        std::cout << "fail - The result is incorrect for element: [" << i << ", " << j
                  << "], expected: " << c_A[i * P + j] << " , but got: " << c_B[i * P + j]
                  << std::endl;
        MismatchFound = true;
      }
    }
  }

  if (!MismatchFound) {
    std::cout << "SUCCESS - The results are correct!" << std::endl;
    return 0;
  } else {
    std::cout << "FAIL - The results mis-match!" << std::endl;
    return -1;
  }
}

//////////////////////////////////////////////////////////////////////////////////////////

int main() {
  std::random_device rd;  // Will be used to obtain a seed for the random number engine
  std::mt19937 gen(rd()); // Standard mersenne_twister_engine seeded with rd()
  std::uniform_real_distribution<> dis(1.0, 2.0);

  // C = alpha * op(A) * op(B)  + beta * C
  oneapi::mkl::transpose transA = oneapi::mkl::transpose::nontrans;
  oneapi::mkl::transpose transB = oneapi::mkl::transpose::nontrans;

  // matrix data sizes
  int m = M;
  int n = P;
  int k = N;

  // leading dimensions of data
  int ldA = k;
  int ldB = n;
  int ldC = n;

  // set scalar fp values
  double alpha = 1.0;
  double beta = 0.0;

  // 1D arrays on host side
  double *A;
  double *B;
  double *C_host_onemkl, *C_cblas;

  A = new double[M * N]{};
  B = new double[N * P]{};
  C_cblas = new double[M * P]{};
  C_host_onemkl = new double[M * P]{};

  // prepare matrix data with ROW-major style
  // A(M, N)
  for (size_t i = 0; i < M; i++)
    for (size_t j = 0; j < N; j++)
      A[i * N + j] = dis(gen);
  // B(N, P)
  for (size_t i = 0; i < N; i++)
    for (size_t j = 0; j < P; j++)
      B[i * P + j] = dis(gen);

  std::cout << "Problem size: c(" << M << "," << P << ") = a(" << M << "," << N << ") * b(" << N
            << "," << P << ")" << std::endl;

  // Resultant matrix: C_cblas
  cblas_dgemm(CblasRowMajor, CblasNoTrans, CblasNoTrans, m, n, k, alpha, A, ldA, B, ldB, beta,
              C_cblas, ldC);

  // Resultant matrix: C_onemkl
  sycl::queue q(sycl::property_list{sycl::property::queue::in_order{}});
  std::cout << "Device: " << q.get_device().get_info<info::device::name>() << std::endl << std::endl;

  double* A_dev        = sycl::malloc_device<double>(M*N, q);
  double* B_dev        = sycl::malloc_device<double>(N*P, q);
  double* C_dev_onemkl = sycl::malloc_device<double>(M*P, q);

  q.memcpy(A_dev, A, (M*N) * sizeof(double));
  q.memcpy(B_dev, B, (N*P) * sizeof(double));

  auto gemm_event = oneapi::mkl::blas::column_major::gemm(q, transB, transA, n, m, k, alpha, B_dev, ldB, A_dev, ldA, beta, C_dev_onemkl, ldC);

  q.memcpy(C_host_onemkl, C_dev_onemkl, (M*P) * sizeof(double));

  q.wait();
  std::cout << "Verify results between OneMKL & CBLAS: ";
  int result_cblas = VerifyResult(C_cblas, C_host_onemkl);

  delete[] A;
  delete[] B;
  delete[] C_cblas;
  delete[] C_host_onemkl;
  sycl::free(A_dev, q);
  sycl::free(B_dev, q);
  sycl::free(C_dev_onemkl, q);
  return result_cblas;
}

Compile and Run

The user would need to provide paths the math-libraris as shown below. Also please provide AOCL library for CPU GEMM by module load aocl. Environment variables MKLROOT is defined with oneapi module & AOCL_ROOT is defined with aocl module. Note: Please pay attention to the linker options for AOCL & oneMKL libraries.

$ clang++ -std=c++17 -sycl-std=2020 -O3 -fsycl -fsycl-targets=nvptx64-nvidia-cuda -Xsycl-target-backend --cuda-gpu-arch=sm_80 -L$AOCL_ROOT/lib -lblis -L$MKLROOT/lib -lonemkl sycl_onemkl_gemm.cpp -o sycl_onemkl_gemm.out