bd12e2b1c6
Implements recursive doubling algorithm for MPI_Scan and MPI_Exscan. The algorithm preserves order of operations so it can be used both by commutative and non-commutative operations. Signed-off-by: Mikhail Kurnosov <mkurnosov@gmail.com>
137 строки
5.0 KiB
C
137 строки
5.0 KiB
C
/*
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* $COPYRIGHT$
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*
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* Additional copyrights may follow
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*
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* $HEADER$
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*/
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#include "ompi_config.h"
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#include "coll_spacc.h"
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#include "mpi.h"
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#include "ompi/constants.h"
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#include "opal/util/bit_ops.h"
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#include "ompi/datatype/ompi_datatype.h"
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#include "ompi/communicator/communicator.h"
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#include "ompi/mca/coll/coll.h"
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#include "ompi/mca/coll/base/coll_base_functions.h"
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#include "ompi/mca/coll/base/coll_tags.h"
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#include "ompi/mca/coll/base/coll_base_util.h"
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#include "ompi/mca/pml/pml.h"
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#include "ompi/op/op.h"
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/*
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* mca_coll_spacc_exscan_intra_recursivedoubling
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*
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* Function: Recursive doubling algorithm for exclusive scan.
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* Accepts: Same as MPI_Exscan
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* Returns: MPI_SUCCESS or error code
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*
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* Description: Implements recursive doubling algorithm for MPI_Exscan.
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* The algorithm preserves order of operations so it can
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* be used both by commutative and non-commutative operations.
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*
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* Example for 5 processes and commutative operation MPI_SUM:
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* Process: 0 1 2 3 4
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* rbuf: - - - - -
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* psend: [0] [1] [2] [3] [4]
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*
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* Step 1:
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* rbuf: - [0] - [2] -
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* psend: [1+0] [0+1] [3+2] [2+3] [4]
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*
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* Step 2:
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* rbuf: - [0] [1+0] [(0+1)+2] -
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* psend: [(3+2)+(1+0)] [(2+3)+(0+1)] [(1+0)+(3+2)] [(1+0)+(2+3)] [4]
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*
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* Step 3:
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* rbuf - [0] [1+0] [(0+1)+2] [(3+2)+(1+0)]
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* psend: [4+((3+2)+(1+0))] [((3+2)+(1+0))+4]
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*
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* Time complexity (worst case): \ceil(\log_2(p))(2\alpha + 2m\beta + 2m\gamma)
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* Memory requirements (per process): 2 * count * typesize = O(count)
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* Limitations: intra-communicators only
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*/
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int mca_coll_spacc_exscan_intra_recursivedoubling(
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const void *sbuf, void *rbuf, int count, struct ompi_datatype_t *dtype,
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struct ompi_op_t *op, struct ompi_communicator_t *comm,
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mca_coll_base_module_t *module)
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{
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int err = MPI_SUCCESS;
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char *tmpsend_raw = NULL, *tmprecv_raw = NULL;
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int comm_size = ompi_comm_size(comm);
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int rank = ompi_comm_rank(comm);
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OPAL_OUTPUT((mca_coll_spacc_stream, "coll:spacc:exscan_intra_recursivedoubling: rank %d/%d",
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rank, comm_size));
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if (count == 0)
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return MPI_SUCCESS;
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if (comm_size < 2)
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return MPI_SUCCESS;
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ptrdiff_t dsize, gap;
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dsize = opal_datatype_span(&dtype->super, count, &gap);
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tmpsend_raw = malloc(dsize);
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tmprecv_raw = malloc(dsize);
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if (NULL == tmpsend_raw || NULL == tmprecv_raw) {
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err = OMPI_ERR_OUT_OF_RESOURCE;
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goto cleanup_and_return;
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}
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char *psend = tmpsend_raw - gap;
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char *precv = tmprecv_raw - gap;
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if (sbuf != MPI_IN_PLACE) {
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err = ompi_datatype_copy_content_same_ddt(dtype, count, psend, sbuf);
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if (MPI_SUCCESS != err) { goto cleanup_and_return; }
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} else {
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err = ompi_datatype_copy_content_same_ddt(dtype, count, psend, rbuf);
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if (MPI_SUCCESS != err) { goto cleanup_and_return; }
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}
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int is_commute = ompi_op_is_commute(op);
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int is_first_block = 1;
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for (int mask = 1; mask < comm_size; mask <<= 1) {
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int remote = rank ^ mask;
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if (remote < comm_size) {
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err = ompi_coll_base_sendrecv(psend, count, dtype, remote,
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MCA_COLL_BASE_TAG_SCAN,
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precv, count, dtype, remote,
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MCA_COLL_BASE_TAG_SCAN, comm,
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MPI_STATUS_IGNORE, rank);
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if (MPI_SUCCESS != err) { goto cleanup_and_return; }
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if (rank > remote) {
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/* Assertion: rank > 0 and rbuf is valid */
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if (is_first_block) {
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err = ompi_datatype_copy_content_same_ddt(dtype, count, rbuf, precv);
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if (MPI_SUCCESS != err) { goto cleanup_and_return; }
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is_first_block = 0;
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} else {
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/* Accumulate prefix reduction: rbuf = precv <op> rbuf */
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ompi_op_reduce(op, precv, rbuf, count, dtype);
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}
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/* Partial result: psend = precv <op> psend */
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ompi_op_reduce(op, precv, psend, count, dtype);
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} else {
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if (is_commute) {
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/* psend = precv <op> psend */
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ompi_op_reduce(op, precv, psend, count, dtype);
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} else {
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/* precv = psend <op> precv */
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ompi_op_reduce(op, psend, precv, count, dtype);
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char *tmp = psend;
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psend = precv;
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precv = tmp;
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}
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}
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}
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}
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cleanup_and_return:
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if (NULL != tmpsend_raw)
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free(tmpsend_raw);
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if (NULL != tmprecv_raw)
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free(tmprecv_raw);
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return err;
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}
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