/* -*- Mode: C; c-basic-offset:4 ; indent-tabs-mode:nil ; -*- */
/*
*
* (C) 2001 by Argonne National Laboratory.
* See COPYRIGHT in top-level directory.
*/
#include "mpiimpl.h"
/* Algorithm: Pairwise Exchange
*
* This pairwise exchange algorithm takes p-1 steps.
*
* We calculate the pairs by using an exclusive-or algorithm:
* for (i=1; i<comm_size; i++)
* dest = rank ^ i;
* This algorithm doesn't work if the number of processes is not a power of
* two. For a non-power-of-two number of processes, we use an
* algorithm in which, in step i, each process receives from (rank-i)
* and sends to (rank+i).
*
* Cost = (p-1).alpha + n.beta
*
* where n is the total amount of data a process needs to send to all
* other processes.
*/
#undef FUNCNAME
#define FUNCNAME MPIR_Alltoall_intra_pairwise
#undef FCNAME
#define FCNAME MPL_QUOTE(FUNCNAME)
int MPIR_Alltoall_intra_pairwise(const void *sendbuf,
int sendcount,
MPI_Datatype sendtype,
void *recvbuf,
int recvcount,
MPI_Datatype recvtype,
MPIR_Comm * comm_ptr, MPIR_Errflag_t * errflag)
{
int comm_size, i, pof2;
MPI_Aint sendtype_extent, recvtype_extent;
int mpi_errno = MPI_SUCCESS, src, dst, rank;
int mpi_errno_ret = MPI_SUCCESS;
MPI_Status status;
if (recvcount == 0)
return MPI_SUCCESS;
comm_size = comm_ptr->local_size;
rank = comm_ptr->rank;
#ifdef HAVE_ERROR_CHECKING
MPIR_Assert(sendbuf != MPI_IN_PLACE);
#endif /* HAVE_ERROR_CHECKING */
/* Get extent of send and recv types */
MPIR_Datatype_get_extent_macro(recvtype, recvtype_extent);
MPIR_Datatype_get_extent_macro(sendtype, sendtype_extent);
/* Make local copy first */
mpi_errno = MPIR_Localcopy(((char *) sendbuf +
rank * sendcount * sendtype_extent),
sendcount, sendtype,
((char *) recvbuf +
rank * recvcount * recvtype_extent), recvcount, recvtype);
if (mpi_errno) {
MPIR_ERR_POP(mpi_errno);
}
/* Is comm_size a power-of-two? */
i = 1;
while (i < comm_size)
i *= 2;
if (i == comm_size)
pof2 = 1;
else
pof2 = 0;
/* Do the pairwise exchanges */
for (i = 1; i < comm_size; i++) {
if (pof2 == 1) {
/* use exclusive-or algorithm */
src = dst = rank ^ i;
} else {
src = (rank - i + comm_size) % comm_size;
dst = (rank + i) % comm_size;
}
mpi_errno = MPIC_Sendrecv(((char *) sendbuf +
dst * sendcount * sendtype_extent),
sendcount, sendtype, dst,
MPIR_ALLTOALL_TAG,
((char *) recvbuf +
src * recvcount * recvtype_extent),
recvcount, recvtype, src,
MPIR_ALLTOALL_TAG, comm_ptr, &status, errflag);
if (mpi_errno) {
/* for communication errors, just record the error but continue */
*errflag =
MPIX_ERR_PROC_FAILED ==
MPIR_ERR_GET_CLASS(mpi_errno) ? MPIR_ERR_PROC_FAILED : MPIR_ERR_OTHER;
MPIR_ERR_SET(mpi_errno, *errflag, "**fail");
MPIR_ERR_ADD(mpi_errno_ret, mpi_errno);
}
}
fn_exit:
if (mpi_errno_ret)
mpi_errno = mpi_errno_ret;
else if (*errflag != MPIR_ERR_NONE)
MPIR_ERR_SET(mpi_errno, *errflag, "**coll_fail");
return mpi_errno;
fn_fail:
goto fn_exit;
}