}
On Apr 17, 2012, at 5:05 AM, Rohan Deshpande wrote:
>
> Hi,
>
> I am trying to distribute large amount of data using MPI.
>
> When I exceed the certain data size the segmentation fault occurs.
>
> Here is my code,
>
>
> #include "mpi.h"
> #include <stdio.h>
> #include <stdlib.h>
> #include <string.h>
> #define ARRAYSIZE 2000000
> #define MASTER 0
>
> int data[ARRAYSIZE];
>
>
> int main(int argc, char* argv[])
> {
> int numtasks, taskid, rc, dest, offset, i, j, tag1, tag2, source, chunksize, namelen;
> int mysum, sum;
> int update(int myoffset, int chunk, int myid);
> char myname[MPI_MAX_PROCESSOR_NAME];
> MPI_Status status;
> double start, stop, time;
> double totaltime;
> FILE *fp;
> char line[128];
> char element;
> int n;
> int k=0;
>
>
>
> /***** Initializations *****/
> MPI_Init(&argc, &argv);
> MPI_Comm_size(MPI_COMM_WORLD, &numtasks);
> MPI_Comm_rank(MPI_COMM_WORLD,&taskid);
> MPI_Get_processor_name(myname, &namelen);
> printf ("MPI task %d has started on host %s...\n", taskid, myname);
> chunksize = (ARRAYSIZE / numtasks);
> tag2 = 1;
> tag1 = 2;
>
>
> /***** Master task only ******/
> if (taskid == MASTER){
>
> /* Initialize the array */
> sum = 0;
> for(i=0; i<ARRAYSIZE; i++) {
> data[i] = i * 1 ;
> sum = sum + data[i];
> }
> printf("Initialized array sum = %d\n",sum);
>
> /* Send each task its portion of the array - master keeps 1st part */
> offset = chunksize;
> for (dest=1; dest<numtasks; dest++) {
> MPI_Send(&offset, 1, MPI_INT, dest, tag1, MPI_COMM_WORLD);
> MPI_Send(&data[offset], chunksize, MPI_INT, dest, tag2, MPI_COMM_WORLD);
> printf("Sent %d elements to task %d offset= %d\n",chunksize,dest,offset);
> offset = offset + chunksize;
> }
>
> /* Master does its part of the work */
> offset = 0;
> mysum = update(offset, chunksize, taskid);
>
> /* Wait to receive results from each task */
> for (i=1; i<numtasks; i++) {
> source = i;
> MPI_Recv(&offset, 1, MPI_INT, source, tag1, MPI_COMM_WORLD, &status);
> MPI_Recv(&data[offset], chunksize, MPI_INT, source, tag2,
> MPI_COMM_WORLD, &status);
> }
>
> /* Get final sum and print sample results */
> MPI_Reduce(&mysum, &sum, 1, MPI_INT, MPI_SUM, MASTER, MPI_COMM_WORLD);
> /* printf("Sample results: \n");
> offset = 0;
> for (i=0; i<numtasks; i++) {
> for (j=0; j<5; j++)
> printf(" %d",data[offset+j]);ARRAYSIZE
> printf("\n");
> offset = offset + chunksize;
> }*/
> printf("\n*** Final sum= %d ***\n",sum);
>
> } /* end of master section */
>
>
> #include <stdlib.h>
> /***** Non-master tasks only *****/
>
> if (taskid > MASTER) {
>
> /* Receive my portion of array from the master task */
> start= MPI_Wtime();
> source = MASTER;
> MPI_Recv(&offset, 1, MPI_INT, source, tag1, MPI_COMM_WORLD, &status);
> MPI_Recv(&data[offset], chunksize, MPI_INT, source, tag2,MPI_COMM_WORLD, &status);
>
> mysum = update(offset, chunksize, taskid);
> stop = MPI_Wtime();
> time = stop -start;
> printf("time taken by process %d to recieve elements and caluclate own sum is = %lf seconds \n", taskid, time);
> totaltime = totaltime + time;
>
> /* Send my results back to the master task */
> dest = MASTER;
> MPI_Send(&offset, 1, MPI_INT, dest, tag1, MPI_COMM_WORLD);
> MPI_Send(&data[offset], chunksize, MPI_INT, MASTER, tag2, MPI_COMM_WORLD);
>
> MPI_Reduce(&mysum, &sum, 1, MPI_INT, MPI_SUM, MASTER, MPI_COMM_WORLD);
>
> } /* end of non-master */
>
> // printf("Total time taken for distribution is - %lf seconds", totaltime);
> MPI_Finalize();
>
> } /* end of main */
>
>
> int update(int myoffset, int chunk, int myid) {
> int i,j;
> int mysum;
> int mydata[myoffset+chunk];
> /* Perform addition to each of my array elements and keep my sum */
> mysum = 0;
> /* printf("task %d has elements:",myid);
> for(j = myoffset; j<myoffset+chunk; j++){
> printf("\t%d", data[j]);
> }
> printf("\n");*/
> for(i=myoffset; i < myoffset + chunk; i++) {
>
> //data[i] = data[i] + i;
> mysum = mysum + data[i];
> }
> printf("Task %d has sum = %d\n",myid,mysum);
> return(mysum);
> }
>
>
> When I run it with ARRAYSIZE = 2000000 The program works fine. But when I increase the size ARRAYSIZE = 20000000. The program ends with segmentation fault.
> I am running it on a cluster (machine 4 is master, machine 5,6 are slaves) and np=20
>
> MPI task 0 has started on host machine4
> MPI task 2 has started on host machine4
> MPI task 3 has started on host machine4
> MPI task 14 has started on host machine4
> MPI task 8 has started on host machine6
> MPI task 10 has started on host machine6
> MPI task 13 has started on host machine4
> MPI task 4 has started on host machine5
> MPI task 6 has started on host machine5
> MPI task 7 has started on host machine5
> MPI task 16 has started on host machine5
> MPI task 11 has started on host machine6
> MPI task 12 has started on host machine4
> MPI task 5 has started on hostmachine5
> MPI task 17 has started on host machine5
> MPI task 18 has started on host machine5
> MPI task 15 has started on host machine4
> MPI task 19 has started on host machine5
> MPI task 1 has started on host machine4
> MPI task 9 has started on host machine6
> Initialized array sum = 542894464
> Sent 1000000 elements to task 1 offset= 1000000
> Task 1 has sum = 1055913696
> time taken by process 1 to recieve elements and caluclate own sum is = 0.249345 seconds
> Sent 1000000 elements to task 2 offset= 2000000
> Sent 1000000 elements to task 3 offset= 3000000
> Task 2 has sum = 328533728
> time taken by process 2 to recieve elements and caluclate own sum is = 0.274285 seconds
> Sent 1000000 elements to task 4 offset= 4000000
> --------------------------------------------------------------------------
> mpirun noticed that process rank 3 with PID 5695 on node machine4 exited on signal 11 (Segmentation fault).
>
> Any idea what could be wrong here?
>
>
> --
>
> Best Regards,
>
> ROHAN DESHPANDE
>
>
>