92 lines
2.5 KiB
C
92 lines
2.5 KiB
C
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#include <stdio.h>
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#include <stdlib.h>
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#include <math.h>
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#include <mpi.h>
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// perform the dot product between the two vectors x and y of size n
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float dot(float x[], float y[], int n);
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int main(int argc, char *argv[])
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{
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int const local_data_size = 5;
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float local_x[local_data_size], local_y[local_data_size];
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float local_dot, global_dot1, global_dot2, reference;
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int borne;
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int my_rank, size;
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MPI_Init(NULL, NULL);
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MPI_Comm_rank(MPI_COMM_WORLD, &my_rank);
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MPI_Comm_size(MPI_COMM_WORLD, &size);
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borne = size * local_data_size - 1;
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reference = (float)(borne * (borne + 1) * (2 * borne + 1) / 6);
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// Initialization of both local vectors with the same values
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// the global vectors would be [0, 1, ..., local_data_size -1]
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for (int i = 0; i < local_data_size; i++)
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{
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local_x[i] = (float)(local_data_size * my_rank + i);
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local_y[i] = (float)(local_data_size * my_rank + i);
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// printf("[MPI process %d] value[%d]: %f\n", my_rank, i, local_x[i]);
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}
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local_dot = dot(local_x, local_y, local_data_size);
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printf("[MPI process %d] my local dot product: %f\n", my_rank, local_dot);
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/* Two-step operation */
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global_dot1 = 0.0;
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// Step 1
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// Use a collective communication to compute the global dot product
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// in such a way that the node 0 gets this value
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MPI_Reduce(&local_dot, &global_dot1, 1, MPI_FLOAT, MPI_SUM, 0, MPI_COMM_WORLD);
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// Node 0 displays the global value and the reference (sum of first integer ^ 2)
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if (my_rank == 0)
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{
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printf("[MPI process %d] *Two-step collective operation* global dot product: %f == %f\n", my_rank, global_dot1, reference);
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}
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// Step 2
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// Use a collective communication to broadcast the global value on each node
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MPI_Bcast(&global_dot1, 1, MPI_FLOAT, 0, MPI_COMM_WORLD);
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// A node i (i different from 0) displays the global value
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if (my_rank != 0)
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{
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printf("[MPI process %d] *Two-step collective operation* global dot product: %f == %f\n", my_rank, global_dot1, reference);
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}
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/* One-step operation */
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global_dot2 = 0;
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// Step 3
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// Now use one single collective communication to perfom both step 1 and 2
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MPI_Allreduce(&local_dot, &global_dot2, 1, MPI_FLOAT, MPI_SUM, MPI_COMM_WORLD);
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// Another node displays the global value
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printf("[MPI process %d] *One-step collective operation* global dot product: %f == %f\n", my_rank, global_dot2, reference);
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MPI_Finalize();
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return EXIT_SUCCESS;
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}
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float dot(float x[], float y[], int n)
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{
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float res = 0.0;
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for (int i = 0; i < n; i++)
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{
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res += x[i] * y[i];
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}
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return res;
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}
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