WIP - SMPI tuto - add parts about sampling and memory sharing

[simgrid.git] / docs / source / tuto_smpi / gemm_mpi.cpp

diff --git a/docs/source/tuto_smpi/gemm_mpi.cpp b/docs/source/tuto_smpi/gemm_mpi.cpp
new file mode 100644 (file)
index 0000000..950e809
--- /dev/null
+++ b/docs/source/tuto_smpi/gemm_mpi.cpp
@@ -0,0 +1,98 @@
+#include "stdio.h"
+#include "mpi.h"
+
+const int size = 3000;
+
+float a[size][size];
+float b[size][size];
+float c[size][size];
+
+void multiply(int istart, int iend)
+{
+    for (int i = istart; i <= iend; ++i){
+        for (int j = 0; j < size; ++j) {
+            for (int k = 0; k < size; ++k) {
+                c[i][j] += a[i][k] * b[k][j];
+            }
+        }
+    }
+}
+
+int main(int argc, char* argv[])
+{
+    int rank, nproc;
+    int istart, iend;
+    double start, end;
+
+    MPI_Init(&argc, &argv);
+    MPI_Comm_size(MPI_COMM_WORLD, &nproc);
+    MPI_Comm_rank(MPI_COMM_WORLD, &rank);
+
+    // MPI_Barrier(MPI_COMM_WORLD);
+    // start = MPI_Wtime();
+
+    if (rank == 0) {
+        // Initialize buffers.
+        for (int i = 0; i < size; ++i) {
+            for (int j = 0; j < size; ++j) {
+                a[i][j] = (float)i + j;
+                b[i][j] = (float)i - j;
+                c[i][j] = 0.0f;
+            }
+        }
+    }
+
+    // Broadcast matrices to all workers.
+    MPI_Bcast(a, size*size, MPI_FLOAT, 0,MPI_COMM_WORLD);
+    MPI_Bcast(b, size*size, MPI_FLOAT, 0,MPI_COMM_WORLD);
+    MPI_Bcast(c, size*size, MPI_FLOAT, 0,MPI_COMM_WORLD);
+
+    // Partition work by i-for-loop.
+    istart = (size / nproc) * rank;
+    iend = (size / nproc) * (rank + 1) - 1;
+
+    // Compute matrix multiplication in [istart,iend]
+    // of i-for-loop.
+    // C <- C + A x B
+    multiply(istart, iend);
+
+    // Gather computed results.
+    MPI_Gather(c + (size/nproc*rank),
+               size*size/nproc,
+               MPI_FLOAT,
+               c + (size/nproc*rank),
+               size*size/nproc,
+               MPI_FLOAT,
+               0,
+               MPI_COMM_WORLD);
+
+    if (rank == 0) {
+        // Compute remaining multiplications
+        // when size % nproc > 0.
+        if (size % nproc > 0) {
+            multiply((size/nproc)*nproc, size-1);
+        }
+    }
+    
+    // MPI_Barrier(MPI_COMM_WORLD);
+    // end = MPI_Wtime();
+
+    MPI_Finalize();
+
+    // if (rank == 0) { /* use time on master node */
+    //     float msec_total = 0.0f;
+
+    //     // Compute and print the performance
+    //     float msec_per_matrix_mul = end-start;
+    //     double flops_per_matrix_mul = 2.0 * (double)size * (double)size * (double)size;
+    //     double giga_flops = (flops_per_matrix_mul * 1.0e-9f) / (msec_per_matrix_mul / 1000.0f);
+    //     printf(
+    //         "Performance= %.2f GFlop/s, Time= %.3f msec, Size= %.0f Ops\n",
+    //         giga_flops,
+    //         msec_per_matrix_mul,
+    //         flops_per_matrix_mul);
+    // }
+   
+
+    return 0;
+}