WIP stencil example

mpi_stencil_gt.cc

@@ -0,0 +1,198 @@
+/*
+ * Test GPU aware MPI on different platforms using a simple
+ * distributed 1d stencil as an example. Gtensor is used so
+ * a single source can be used for all platforms.
+ */
+
+#include <cmath>
+#include <mpi.h>
+#include <stdio.h>
+#include <stdlib.h>
+
+#include "gtensor/gtensor.h"
+#include "gtensor/reductions.h"
+
+using namespace gt::placeholders;
+
+// little hack to make code parameterizable on managed vs device memory
+namespace gt
+{
+
+namespace ext
+{
+
+namespace detail
+{
+
+template <typename T, gt::size_type N, typename S = gt::space::device>
+struct gthelper
+{
+  using gtensor = gt::gtensor<T, N, S>;
+};
+
+#ifdef GTENSOR_HAVE_DEVICE
+
+template <typename T, gt::size_type N>
+struct gthelper<T, N, gt::space::managed>
+{
+  using gtensor = gt::gtensor_container<gt::space::managed_vector<T>, N>;
+};
+#endif
+
+} // namespace detail
+
+template <typename T, gt::size_type N, typename S = gt::space::device>
+using gtensor2 = typename detail::gthelper<T, N, S>::gtensor;
+
+} // namespace ext
+
+} // namespace gt
+
+static const gt::gtensor<double, 1> stencil5 = {1.0 / 12.0, -2.0 / 3.0, 0.0,
+                                                2.0 / 3.0, -1.0 / 12.0};
+
+/*
+ * Return unevaluated expression that calculates the stencil.
+ *
+ * Size of the result will be size of y minus 4 (the number of boundary points).
+ */
+inline auto stencil1d_5(const gt::gtensor_device<double, 1>& y,
+                        const gt::gtensor<double, 1>& stencil)
+{
+  return stencil(0) * y.view(_s(0, -4)) + stencil(1) * y.view(_s(1, -3)) +
+         stencil(2) * y.view(_s(2, -2)) + stencil(3) * y.view(_s(3, -1)) +
+         stencil(4) * y.view(_s(4, _));
+}
+
+void set_rank_device(int n_ranks, int rank)
+{
+  int n_devices, device, ranks_per_device;
+
+  n_devices = gt::backend::clib::device_get_count();
+
+  if (n_ranks > n_devices) {
+    if (n_ranks % n_devices != 0) {
+      printf("ERROR: Number of ranks (%d) not a multiple of number of GPUs "
+             "(%d)\n_global",
+             n_ranks, n_devices);
+      exit(EXIT_FAILURE);
+    }
+    ranks_per_device = n_ranks / n_devices;
+    device = rank / ranks_per_device;
+  } else {
+    ranks_per_device = 1;
+    device = rank;
+  }
+
+  gt::backend::clib::device_set(device);
+}
+
+void boundary_exchange(MPI_Comm comm, int world_size, int rank,
+                       gt::gtensor_device<double, 1>& d_y, int n_bnd)
+{
+  double* d_y_data = gt::raw_pointer_cast(d_y.data());
+  double* d_y_data_end = gt::raw_pointer_cast(d_y.data()) + d_y.size();
+
+  MPI_Request req_l[2];
+  MPI_Request req_r[2];
+
+  int rank_l = rank - 1;
+  int rank_r = rank + 1;
+
+  if (rank_l >= 0) {
+    printf("%d left\n", rank);
+    // send/recv left boundary
+    MPI_Irecv(d_y_data, n_bnd, MPI_DOUBLE, rank_l, 123, comm,
+              &req_l[0]);
+    MPI_Isend(d_y_data + n_bnd, n_bnd, MPI_DOUBLE, rank_l, 456, comm,
+              &req_l[1]);
+  }
+
+  if (rank_r < world_size) {
+    printf("%d right\n", rank);
+    // send/recv right boundary
+    MPI_Irecv(d_y_data_end - n_bnd, n_bnd, MPI_DOUBLE, rank_r, 456,
+              comm, &req_r[0]);
+    MPI_Isend(d_y_data - 2 * n_bnd, n_bnd, MPI_DOUBLE, rank_r, 123,
+              comm, &req_r[1]);
+  }
+
+  int mpi_rval;
+  if (rank_l >= 0) {
+    printf("%d wait left\n", rank);
+    mpi_rval = MPI_Waitall(2, req_l, MPI_STATUSES_IGNORE);
+    if (mpi_rval != MPI_SUCCESS) {
+      printf("send_l error: %d\n", mpi_rval);
+    }
+  }
+  if (rank_r < world_size) {
+    printf("%d wait right\n", rank);
+    mpi_rval = MPI_Waitall(2, req_r, MPI_STATUSES_IGNORE);
+    if (mpi_rval != MPI_SUCCESS) {
+      printf("send_r error: %d\n", mpi_rval);
+    }
+  }
+}
+
+int main(int argc, char** argv)
+{
+  constexpr int n_global = 1024 * 1024 * 1024;
+  constexpr int n_sten = 5;
+  constexpr int n_bnd = (n_sten - 1) / 2;
+  int world_size, world_rank, device_id;
+  uint32_t vendor_id;
+
+  MPI_Init(NULL, NULL);
+
+  MPI_Comm_size(MPI_COMM_WORLD, &world_size);
+  MPI_Comm_rank(MPI_COMM_WORLD, &world_rank);
+
+  const int n_local = n_global / world_size;
+  const int n_local_with_ghost = n_local + 2 * n_bnd;
+
+  set_rank_device(world_size, world_rank);
+  device_id = gt::backend::clib::device_get();
+  vendor_id = gt::backend::clib::device_get_vendor_id(device_id);
+
+  auto h_y = gt::empty<double>({n_local_with_ghost});
+  auto d_y = gt::empty_device<double>({n_local_with_ghost});
+
+  auto h_dydx_numeric = gt::empty<double>({n_local});
+  auto h_dydx_actual = gt::empty<double>({n_local});
+  auto d_dydx_numeric = gt::empty_device<double>({n_local});
+
+  double lx = 8;
+  double dx = lx / n_global;
+  double lx_local = lx / world_rank;
+  double scale = n_global / lx;
+  auto fn_x_cubed = [](double x) { return x * x * x; };
+  auto fn_x_cubed_deriv = [](double x) { return 3 * x * x; };
+
+  printf("%d Init\n", world_rank);
+  double x_start = world_rank * lx_local;
+  for (int i = 0; i < n_local; i++) {
+    double xtmp = x_start + i * dx;
+    h_y(i + n_bnd) = fn_x_cubed(xtmp);
+    h_dydx_actual(i) = fn_x_cubed_deriv(xtmp);
+  }
+
+  printf("%d Ex\n", world_rank);
+
+  boundary_exchange(MPI_COMM_WORLD, world_size, world_rank, d_y, n_bnd);
+
+  printf("%d Sten\n", world_rank);
+  //d_dydx_numeric = stencil1d_5(d_y, stencil5) * scale;
+
+  printf("Copy\n");
+  gt::copy(d_dydx_numeric, h_dydx_numeric);
+
+  printf("Err calc\n");
+  double err_norm = std::sqrt(gt::sum_squares(h_dydx_numeric - h_dydx_actual));
+
+  printf("%d/%d [%d:0x%08x] err_norm = %f\n", world_rank, world_size, device_id,
+         vendor_id, err_norm);
+
+  MPI_Finalize();
+
+  return EXIT_SUCCESS;
+}