Hello,
Could someone explain, why the following code works for MSG_SIZE=4096, but does
no work for MSG_SIZE=16384. The messages are composed of doubles, so the bigger
message has 131072 bytes length, which, as far as I know, involves rendez-vous
communication protocol for implementation of communications.
#include <stdio.h>
#include <stdlib.h>
#include <mpi.h>
//#define MSG_SIZE 16384
#define MSG_SIZE 4096
int main(int argc, char** argv){
int iMyRank, iPeerRank;
int iIntTypeSize, iDoubleTypeSize, iRecvdCount;
double* pdBufIn, *pdBufOut;
MPI_Status status1, status2;
MPI_Init(&argc,&argv);
MPI_Comm_rank(MPI_COMM_WORLD,&iMyRank);
MPI_Type_size(MPI_INT,&iIntTypeSize);
MPI_Type_size(MPI_DOUBLE,&iDoubleTypeSize);
if( sizeof(double) != iDoubleTypeSize ) {fprintf(stderr,"Different sizes
for DOUBLE type\n"); return 0;}
if( sizeof(int) != iIntTypeSize ) {fprintf(stderr,"Different sizes for INT
type\n"); return 0;}
pdBufIn = (double *)calloc(MSG_SIZE,sizeof(double));
pdBufOut = (double *)calloc(MSG_SIZE,sizeof(double));
fprintf(stderr,"%d: start %d bytes\n", iMyRank, MSG_SIZE*iDoubleTypeSize);
fflush(stderr);
if(iMyRank==0){
MPI_Send(&iMyRank,1,MPI_INT,1,10,MPI_COMM_WORLD);
MPI_Send(pdBufOut,MSG_SIZE,MPI_DOUBLE,1,30,MPI_COMM_WORLD);
MPI_Recv(&iPeerRank,1,MPI_INT,MPI_ANY_SOURCE,11,MPI_COMM_WORLD,&status1);
MPI_Recv(pdBufIn,MSG_SIZE,MPI_DOUBLE,status1.MPI_SOURCE,31,MPI_COMM_WORLD,&status2);
}else{
MPI_Send(&iMyRank,1,MPI_INT,0,11,MPI_COMM_WORLD);
MPI_Send(pdBufOut,MSG_SIZE,MPI_DOUBLE,0,31,MPI_COMM_WORLD);
MPI_Recv(&iPeerRank,1,MPI_INT,MPI_ANY_SOURCE,10,MPI_COMM_WORLD,&status1);
MPI_Recv(pdBufIn,MSG_SIZE,MPI_DOUBLE,status1.MPI_SOURCE,30,MPI_COMM_WORLD,&status2);
}
fprintf(stderr,"%d: done\n",iMyRank);
MPI_Finalize();
return 0;
}
Thanks!
Anton
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