/* -*- Mode: C; c-basic-offset:4 ; indent-tabs-mode:nil ; -*- */
/*
*
* (C) 2017 by Argonne National Laboratory.
* See COPYRIGHT in top-level directory.
*/
/* This implementation of MPI_Reduce_scatter_block was obtained by taking
the implementation of MPI_Reduce_scatter from reduce_scatter.c and replacing
recvcnts[i] with recvcount everywhere. */
#include "mpiimpl.h"
#undef FUNCNAME
#define FUNCNAME MPIR_Reduce_scatter_block_intra_pairwise
#undef FCNAME
#define FCNAME MPL_QUOTE(FUNCNAME)
/* Algorithm: Pairwise Exchange
*
* This is a pairwise exchange algorithm similar to
* the one used in MPI_Alltoall. At step i, each process sends n/p amount of
* data to (rank+i) and receives n/p amount of data from (rank-i).
*
* Cost = (p-1).alpha + n.((p-1)/p).beta + n.((p-1)/p).gamma
*/
int MPIR_Reduce_scatter_block_intra_pairwise(const void *sendbuf,
void *recvbuf,
int recvcount,
MPI_Datatype datatype,
MPI_Op op,
MPIR_Comm * comm_ptr, MPIR_Errflag_t * errflag)
{
int rank, comm_size, i;
MPI_Aint extent, true_extent, true_lb;
int *disps;
void *tmp_recvbuf;
int mpi_errno = MPI_SUCCESS;
int mpi_errno_ret = MPI_SUCCESS;
int src, dst;
MPIR_CHKLMEM_DECL(5);
comm_size = comm_ptr->local_size;
rank = comm_ptr->rank;
/* set op_errno to 0. stored in perthread structure */
{
MPIR_Per_thread_t *per_thread = NULL;
int err = 0;
MPID_THREADPRIV_KEY_GET_ADDR(MPIR_ThreadInfo.isThreaded, MPIR_Per_thread_key,
MPIR_Per_thread, per_thread, &err);
MPIR_Assert(err == 0);
per_thread->op_errno = 0;
}
if (recvcount == 0) {
goto fn_exit;
}
MPIR_Datatype_get_extent_macro(datatype, extent);
MPIR_Type_get_true_extent_impl(datatype, &true_lb, &true_extent);
#ifdef HAVE_ERROR_CHECKING
{
int is_commutative;
is_commutative = MPIR_Op_is_commutative(op);
MPIR_Assert(is_commutative);
}
#endif /* HAVE_ERROR_CHECKING */
MPIR_CHKLMEM_MALLOC(disps, int *, comm_size * sizeof(int), mpi_errno, "disps", MPL_MEM_BUFFER);
for (i = 0; i < comm_size; i++) {
disps[i] = i * recvcount;
}
/* commutative and long message, or noncommutative and long message.
* use (p-1) pairwise exchanges */
if (sendbuf != MPI_IN_PLACE) {
/* copy local data into recvbuf */
mpi_errno = MPIR_Localcopy(((char *) sendbuf + disps[rank] * extent),
recvcount, datatype, recvbuf, recvcount, datatype);
if (mpi_errno)
MPIR_ERR_POP(mpi_errno);
}
/* allocate temporary buffer to store incoming data */
MPIR_CHKLMEM_MALLOC(tmp_recvbuf, void *, recvcount * (MPL_MAX(true_extent, extent)) + 1,
mpi_errno, "tmp_recvbuf", MPL_MEM_BUFFER);
/* adjust for potential negative lower bound in datatype */
tmp_recvbuf = (void *) ((char *) tmp_recvbuf - true_lb);
for (i = 1; i < comm_size; i++) {
src = (rank - i + comm_size) % comm_size;
dst = (rank + i) % comm_size;
/* send the data that dst needs. recv data that this process
* needs from src into tmp_recvbuf */
if (sendbuf != MPI_IN_PLACE)
mpi_errno = MPIC_Sendrecv(((char *) sendbuf + disps[dst] * extent),
recvcount, datatype, dst,
MPIR_REDUCE_SCATTER_BLOCK_TAG, tmp_recvbuf,
recvcount, datatype, src,
MPIR_REDUCE_SCATTER_BLOCK_TAG, comm_ptr,
MPI_STATUS_IGNORE, errflag);
else
mpi_errno = MPIC_Sendrecv(((char *) recvbuf + disps[dst] * extent),
recvcount, datatype, dst,
MPIR_REDUCE_SCATTER_BLOCK_TAG, tmp_recvbuf,
recvcount, datatype, src,
MPIR_REDUCE_SCATTER_BLOCK_TAG, comm_ptr,
MPI_STATUS_IGNORE, 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);
}
if (sendbuf != MPI_IN_PLACE) {
mpi_errno = MPIR_Reduce_local(tmp_recvbuf, recvbuf, recvcount, datatype, op);
} else {
mpi_errno = MPIR_Reduce_local(tmp_recvbuf, ((char *) recvbuf + disps[rank] * extent),
recvcount, datatype, op);
/* we can't store the result at the beginning of
* recvbuf right here because there is useful data
* there that other process/processes need. at the
* end, we will copy back the result to the
* beginning of recvbuf. */
}
}
/* if MPI_IN_PLACE, move output data to the beginning of
* recvbuf. already done for rank 0. */
if ((sendbuf == MPI_IN_PLACE) && (rank != 0)) {
mpi_errno = MPIR_Localcopy(((char *) recvbuf +
disps[rank] * extent),
recvcount, datatype, recvbuf, recvcount, datatype);
if (mpi_errno)
MPIR_ERR_POP(mpi_errno);
}
fn_exit:
MPIR_CHKLMEM_FREEALL();
{
MPIR_Per_thread_t *per_thread = NULL;
int err = 0;
MPID_THREADPRIV_KEY_GET_ADDR(MPIR_ThreadInfo.isThreaded, MPIR_Per_thread_key,
MPIR_Per_thread, per_thread, &err);
MPIR_Assert(err == 0);
if (per_thread->op_errno)
mpi_errno = per_thread->op_errno;
}
/* --BEGIN ERROR HANDLING-- */
if (mpi_errno_ret)
mpi_errno = mpi_errno_ret;
else if (*errflag != MPIR_ERR_NONE)
MPIR_ERR_SET(mpi_errno, *errflag, "**coll_fail");
/* --END ERROR HANDLING-- */
return mpi_errno;
fn_fail:
goto fn_exit;
}