CoE Cluster november 2011/MPI

Programmering med MPI

http://www.lam-mpi.org/tutorials/one-step/ezstart.php

Geany IDE

Der findes et IDE man kan tilrette til cluster kompilering og eksekvering kaldet geany. Installation:

aptitude install geany

For at kompilere det med mpicc og eksekvere med mpiexec skal man lige rette lidt til under "Build > Set Includes and Arguments".

Geany IDE

mpicc -Wall "%f" -o "%e"

mpiexec -n 20 -hostfile ~/mpd.hosts "%e"

Og til C++ bruger man mpic++ -Wall "%f" -o "%e"

Programmet man skriver skal selvfølgelig ligge i /var/mirror for de andre noder også har adgang til det.

Og den kan man selvfølgelig X'e over med

env DISPLAY=172.16.4.105:1 geany

Hello World eksempel

HelloWorld program

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

int main (int argc, char *argv[] )
{
        int rank, size, namelen;
        char processor_name[MPI_MAX_PROCESSOR_NAME];


        MPI_Init( &argc, &argv );

        MPI_Get_processor_name( processor_name, &namelen );
        MPI_Comm_rank( MPI_COMM_WORLD, &rank );
        MPI_Comm_size( MPI_COMM_WORLD, &size );
        printf( "Hello World from process %d, of %d on %s\n", rank, size, processor_name );
        MPI_Finalize();
        return 0;
}

Compile det med

 mpicxx -o helloWorld helloWorld.c

og kør det med

mpiexec -n 10 /var/mirror/helloWorld

Resultatet skulle gerne blive

Hello World from process 2, of 10 on C05
Hello World from process 6, of 10 on C05
Hello World from process 3, of 10 on C06
Hello World from process 1, of 10 on C04
Hello World from process 5, of 10 on C04
Hello World from process 7, of 10 on C06
Hello World from process 9, of 10 on C04
Hello World from process 0, of 10 on C01
Hello World from process 4, of 10 on C01
Hello World from process 8, of 10 on C01

Hello World med MPI

Det forrige eksempel brugte ikke rigtig MPI til noget, ud over at få rank og size.
Hvis vi skal lave det om til at rank 0 er den der printer til skærmen og alle de andre sender via MPI til den, ville det se sådan ud:

#include "mpi.h"
#include <stdio.h>
#include <string.h>

int main (int argc, char *argv[] )
{
        int rank, size, namelen, i;
        char processor_name[MPI_MAX_PROCESSOR_NAME];
        char greeting[MPI_MAX_PROCESSOR_NAME + 100];
        MPI_Status status;

        MPI_Init( &argc, &argv );

        MPI_Get_processor_name( processor_name, &namelen );
        MPI_Comm_rank( MPI_COMM_WORLD, &rank );
        MPI_Comm_size( MPI_COMM_WORLD, &size );
        sprintf( greeting,  "Hello World from process %d, of %d on %s\n", rank, size, processor_name );

        if ( rank == 0 ) {
                printf( "%s", greeting );
                for (i = 1; i < size; i++ ) {
                        MPI_Recv( greeting, sizeof( greeting ), MPI_CHAR, i, 1, MPI_COMM_WORLD, &status );
                        printf( "%s", greeting );
                }
        }
        else {
                MPI_Send( greeting, strlen( greeting ) + 1, MPI_CHAR, 0, 1, MPI_COMM_WORLD );
        }
        MPI_Finalize();
        return 0;
}

Hvilket returnenrer:

0: Hello World from process 0, of 10 on C01
0: Hello World from process 1, of 10 on C04
0: Hello World from process 2, of 10 on C05
0: Hello World from process 3, of 10 on C06
0: Hello World from process 4, of 10 on C01
0: Hello World from process 5, of 10 on C04
0: Hello World from process 6, of 10 on C05
0: Hello World from process 7, of 10 on C06
0: Hello World from process 8, of 10 on C01
0: Hello World from process 9, of 10 on C04