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/*
* Copyright (C) 2010. See COPYRIGHT in top-level directory.
*/
#include <stdio.h>
#include <stdlib.h>
#include <assert.h>
#include <mpi.h>
#define INTERCOMM_TAG 0
#define NITER 1024
void pgroup_create(int grp_size, int *pid_list, MPI_Comm *group_out);
void pgroup_free(MPI_Comm *group);
/** Free a pgroup
*/
void pgroup_free(MPI_Comm *group) {
/* Note: It's ok to compare predefined handles */
if (*group == MPI_COMM_NULL || *group == MPI_COMM_SELF)
return;
MPI_Comm_free(group);
}
/* Create a processor group containing the processes in pid_list.
*
* NOTE: pid_list list must be identical and sorted on all processes
*/
void pgroup_create(int grp_size, int *pid_list, MPI_Comm *group_out) {
int i, grp_me, me, nproc, merge_size;
MPI_Comm pgroup, inter_pgroup;
MPI_Comm_rank(MPI_COMM_WORLD, &me);
MPI_Comm_size(MPI_COMM_WORLD, &nproc);
/* CASE: pgroup size 0 */
if (grp_size == 0) {
*group_out = MPI_COMM_NULL;
return;
}
/* CASE: pgroup size 1 */
else if (grp_size == 1 && pid_list[0] == me) {
*group_out = MPI_COMM_SELF;
return;
}
/* CHECK: If I'm not a member, return COMM_NULL */
grp_me = -1;
for (i = 0; i < grp_size; i++) {
if (pid_list[i] == me) {
grp_me = i;
break;
}
}
if (grp_me < 0) {
*group_out = MPI_COMM_NULL;
return;
}
pgroup = MPI_COMM_SELF;
for (merge_size = 1; merge_size < grp_size; merge_size *= 2) {
int gid = grp_me / merge_size;
MPI_Comm pgroup_old = pgroup;
if (gid % 2 == 0) {
/* Check if right partner doesn't exist */
if ((gid+1)*merge_size >= grp_size)
continue;
MPI_Intercomm_create(pgroup, 0, MPI_COMM_WORLD, pid_list[(gid+1)*merge_size], INTERCOMM_TAG, &inter_pgroup);
MPI_Intercomm_merge(inter_pgroup, 0 /* LOW */, &pgroup);
} else {
MPI_Intercomm_create(pgroup, 0, MPI_COMM_WORLD, pid_list[(gid-1)*merge_size], INTERCOMM_TAG, &inter_pgroup);
MPI_Intercomm_merge(inter_pgroup, 1 /* HIGH */, &pgroup);
}
MPI_Comm_free(&inter_pgroup);
if (pgroup_old != MPI_COMM_SELF) MPI_Comm_free(&pgroup_old);
}
*group_out = pgroup;
}
int main(int argc, char **argv) {
int me, nproc, i, j, *glist;
MPI_Comm groups[NITER];
MPI_Group world_group;
MPI_Init(&argc, &argv);
MPI_Comm_rank(MPI_COMM_WORLD, &me);
MPI_Comm_size(MPI_COMM_WORLD, &nproc);
MPI_Comm_group(MPI_COMM_WORLD, &world_group);
glist = (int*) malloc(nproc*sizeof(int));
for (i = 0; i < nproc; i++)
glist[i] = i;
if (me == 0)
printf("Gsize\tPGgroup (sec)\tComm (sec)\n");
MPI_Barrier(MPI_COMM_WORLD);
for (i = 1; i <= nproc; i*= 2) {
double t_start, t_pg, t_comm;
MPI_Group intracomm_group;
/** Benchmark pgroup creation cost **/
MPI_Barrier(MPI_COMM_WORLD);
t_start = MPI_Wtime();
for (j = 0; j < NITER; j++)
pgroup_create(i, glist, &groups[j]);
t_pg = MPI_Wtime() - t_start;
for (j = 0; j < NITER; j++)
pgroup_free(&groups[j]);
/** Benchmark intracommunicator creation cost **/
MPI_Group_incl(world_group, i, glist, &intracomm_group);
MPI_Barrier(MPI_COMM_WORLD);
t_start = MPI_Wtime();
for (j = 0; j < NITER; j++)
MPI_Comm_create(MPI_COMM_WORLD, intracomm_group, &groups[j]);
t_comm = MPI_Wtime() - t_start;
MPI_Group_free(&intracomm_group);
for (j = 0; j < NITER; j++)
pgroup_free(&groups[j]);
if (me == 0)
printf("%6d\t%0.9f\t%0.9f\n", i, t_pg/NITER, t_comm/NITER);
}
free(glist);
MPI_Group_free(&world_group);
MPI_Finalize();
return 0;
}
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