code example
MPI message passing interface
two-sided communication.
POSIX threads
Cell Cell Broadband Engine
file sub1.h: common interface
class data1 {
public:
   data1() {}
   int n0, n1;
   float *x, *y;
   float e;
   int pad[27];// pad to 128 byte length
};
file spe1.cc: SPU code
#include <spu_mfcio.h>
#include "sub1.h"
#define BLOCK (2048)
int main(unsigned long long id,
     unsigned long long argp, unsigned long long envp) {
  data1 vec __attribute__ (aligned(128));
  // read parameter
  mfc_get(&vec, (unsigned int)argp, sizeof(data1), 1, 0, 0);
  mfc_write_tag_mask(0xffffffff);
  mfc_read_tag_status_all();// wait for data transfer
  float e = 0;
  // allocate double buffer in local SPU memory
  float *x = (float*)malloc(BLOCK*sizeof(float));
  float *x0 = (float*)malloc(BLOCK*sizeof(float));
  float *y = (float*)malloc((BLOCK+32)*sizeof(float)) + 1;
  float *y0 = (float*)malloc((BLOCK+32)*sizeof(float)) + 1;
  // get first buffer
  mfc_get(x, &vec.x[vec.n0], BLOCK*sizeof(float), 2, 0, 0);
  mfc_get(y-1, &vec.y[vec.n0], (BLOCK+32)*sizeof(float), 3, 0, 0);
  mfc_read_tag_status_all();
  for (int ib=vec.n0; ib<vec.n1; ib += BLOCK) {
   if (ib+BLOCK<vec.n1) {
    // get next buffer, fence after put x
    mfc_getf(x0, &vec.x[ib+BLOCK], BLOCK*sizeof(float), 2, 0, 0);
    mfc_get(y0-1, &vec.y[ib+BLOCK], (BLOCK+32)*sizeof(float), 3, 0, 0);
   }
  // do computation
  for (int i=0; iBLOCK; ++i) {
   x[i] += ( y[i+1] + y[i-1] )*.5;
   e += y[i] * y[i];
  }
   mfc_read_tag_status_all(); // wait for data transfer
   // put current buffer
   mfc_put(x, &vec.x[ib], BLOCK*sizeof(float), 2, 0, 0);
   float *t = x; x = x0; x0 = t;
   t = y; y = y0; y0 = t; // swap buffers
  }
  // put reduction value
  vec.e = e;
  mfc_put(&vec, argp, sizeof(data1), 1, 0, 0);
  mfc_read_tag_status_all(); // wait for data transfer
  return 0;
}
main file
#include <mpi.h>
#include <pthread.h>
#include <libspe2.h>
#include "sub1.h"

float *x, *y;
#define PROC (8)
float e_vec[PROC];
int n_thread0, n_thread1;

extern spe_program_handle_t spe1; // defined in SPU code
void *thread1(void *arg) {
  int p = (int)arg;
  int n0 = n_thread0 + (p * (n_thread1-n_thread0)) / PROC;
  int n1 = n_thread0 + ((p+1) * (n_thread1-n_thread0)) / PROC;
  data1 block __attribute__ (aligned(128));
  spe_context_ptr_t ctxs;
  spe_stop_info_t st;
  ctxs = spe_context_create(0, NULL);
  spe_program_load (ctxs, &spe1);
  block.n0 = n0;
  block.n1 = n1;
  block.x = &x[n0];
  block.y = &y[n0-1];
  unsigned int entry = SPE_DEFAULT_ENTRY;
  float e = 0;
  // execute code on a single SPU and wait for termination
  spe_context_run(ctxs[p], &entry, 0, &block, NULL, st);
  spe_context_destroy(ctxs);
  e += block.e;
  e_vec[p] = e;
  return (void*) 0;
}

int main(int argc, char *argv[]) {
  int n = ...;
  MPI_Init(&argc, &argv);
  int numproc, me;
  MPI_Comm_size(MPI_COMM_WORLD, &numproc);
  MPI_Comm_rank(MPI_COMM_WORLD, &me);
  int p_left = -1, p_right = -1;
  if (me > 0)
   p_left = me-1;
  if (me < numproc-1)
   p_right = me+1;
  int n_local0 = 1 + (me * (n-1)) / numproc;
  int n_local1 = 1 + ((me+1) * (n-1)) / numproc;
  // allocate only local part + ghost zone of the arrays x,y
  float *x, *y;
  x = new float[n_local1 - n_local0 + 2];
  y = new float[n_local1 - n_local0 + 2];
  x -= (n_local0 - 1);
  y -= (n_local0 - 1);

  ... // fill x, y

  // fill ghost zone
  MPI_Status s;
  if (p_left != -1)
    MPI_Send(&y[n_local0], 1, MPI_FLOAT, p_left,
      1, MPI_COMM_WORLD);
  if (p_right != -1) {
    MPI_Recv(&y[n_local1], 1, MPI_FLOAT, p_right,
      1, MPI_COMM_WORLD, &s);
    MPI_Send(&y[n_local1-1], 1, MPI_FLOAT, p_right,
      2, MPI_COMM_WORLD);
  }
  if (p_left != -1)
    MPI_Recv(&y[n_local0-1], 1, MPI_FLOAT, p_left,
      2, MPI_COMM_WORLD, &s);
 

  pthread_t threads[PROC];
  pthread_attr_t attr;
  pthread_attr_init(&attr);
  n_thread0 = n_local0;
  n_thread1 = n_local1;
  float e = 0;
  // start threads and wait for termination
  for (int p=0; p<PROC; ++p)
   pthread_create(&threads[p], &attr, thread1, (void *)p);
  for (int p=0; p<PROC; ++p) {
   pthread_join(threads[p], NULL);
   e += e_vec[p];
  }

  float e_local = e;
  MPI_Allreduce(&e_local, &e, 1, MPI_FLOAT, MPI_SUM, MPI_COMM_WORLD);

  ... // output x, e

  x += (n_local0 - 1);
  y += (n_local0 - 1);
  delete[] x, y;
  MPI_Finalize();
  return 0;
}
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