/
coll_base_reduce_scatter_block.c
973 lines (905 loc) · 41.7 KB
/
coll_base_reduce_scatter_block.c
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/* -*- Mode: C; c-basic-offset:4 ; indent-tabs-mode:nil -*- */
/*
* Copyright (c) 2004-2005 The Trustees of Indiana University and Indiana
* University Research and Technology
* Corporation. All rights reserved.
* Copyright (c) 2004-2017 The University of Tennessee and The University
* of Tennessee Research Foundation. All rights
* reserved.
* Copyright (c) 2004-2005 High Performance Computing Center Stuttgart,
* University of Stuttgart. All rights reserved.
* Copyright (c) 2004-2005 The Regents of the University of California.
* All rights reserved.
* Copyright (c) 2008 Sun Microsystems, Inc. All rights reserved.
* Copyright (c) 2012 Oak Ridge National Labs. All rights reserved.
* Copyright (c) 2012 Sandia National Laboratories. All rights reserved.
* Copyright (c) 2014-2018 Research Organization for Information Science
* and Technology (RIST). All rights reserved.
* Copyright (c) 2018 Siberian State University of Telecommunications
* and Information Sciences. All rights reserved.
* Copyright (c) 2022 IBM Corporation. All rights reserved.
* Copyright (c) 2023 Jeffrey M. Squyres. All rights reserved.
* $COPYRIGHT$
*
* Additional copyrights may follow
*
* $HEADER$
*/
#include "ompi_config.h"
#include "mpi.h"
#include "opal/util/bit_ops.h"
#include "ompi/constants.h"
#include "ompi/datatype/ompi_datatype.h"
#include "ompi/communicator/communicator.h"
#include "ompi/mca/coll/coll.h"
#include "ompi/mca/coll/basic/coll_basic.h"
#include "ompi/mca/pml/pml.h"
#include "ompi/op/op.h"
#include "coll_tags.h"
#include "coll_base_functions.h"
#include "coll_base_topo.h"
#include "coll_base_util.h"
/*
* ompi_reduce_scatter_block_basic_linear
*
* Function: - reduce then scatter
* Accepts: - same as MPI_Reduce_scatter_block()
* Returns: - MPI_SUCCESS or error code
*
* Algorithm:
* reduce and scatter (needs to be cleaned
* up at some point)
*/
int
ompi_coll_base_reduce_scatter_block_basic_linear(const void *sbuf, void *rbuf, int rcount,
struct ompi_datatype_t *dtype,
struct ompi_op_t *op,
struct ompi_communicator_t *comm,
mca_coll_base_module_t *module)
{
int rank, size, err = OMPI_SUCCESS;
size_t count;
ptrdiff_t gap, span;
char *recv_buf = NULL, *recv_buf_free = NULL;
/* Initialize */
rank = ompi_comm_rank(comm);
size = ompi_comm_size(comm);
/* short cut the trivial case */
count = rcount * (size_t)size;
if (0 == count) {
return OMPI_SUCCESS;
}
/* Handle MPI_IN_PLACE */
if (MPI_IN_PLACE == sbuf) {
sbuf = rbuf;
}
/*
* For large payload (defined as a count greater than INT_MAX)
* to reduce the memory footprint on the root we segment the
* reductions per rank, then send to each rank.
*
* Additionally, sending the message in the coll_reduce() as
* "rcount*size" would exceed the 'int count' parameter in the
* coll_reduce() function. So another technique is required
* for count values that exceed INT_MAX.
*/
if ( OPAL_UNLIKELY(count > INT_MAX) ) {
int i;
void *sbuf_ptr;
/* Get datatype information for an individual block */
span = opal_datatype_span(&dtype->super, rcount, &gap);
if (0 == rank) {
/* temporary receive buffer. See coll_basic_reduce.c for
details on sizing */
recv_buf_free = (char*) malloc(span);
if (NULL == recv_buf_free) {
err = OMPI_ERR_OUT_OF_RESOURCE;
goto cleanup;
}
recv_buf = recv_buf_free - gap;
}
for( i = 0; i < size; ++i ) {
/* Calculate the portion of the send buffer to reduce over */
sbuf_ptr = (char*)sbuf + span * (size_t)i;
/* Reduction for this peer */
err = comm->c_coll->coll_reduce(sbuf_ptr, recv_buf, rcount,
dtype, op, 0, comm,
comm->c_coll->coll_reduce_module);
if (MPI_SUCCESS != err) {
goto cleanup;
}
/* Send reduce results to this peer */
if (0 == rank ) {
if( i == rank ) {
err = ompi_datatype_copy_content_same_ddt(dtype, rcount, rbuf, recv_buf);
} else {
err = MCA_PML_CALL(send(recv_buf, rcount, dtype, i,
MCA_COLL_BASE_TAG_REDUCE_SCATTER_BLOCK,
MCA_PML_BASE_SEND_STANDARD, comm));
}
if (MPI_SUCCESS != err) {
goto cleanup;
}
}
else if( i == rank ) {
err = MCA_PML_CALL(recv(rbuf, rcount, dtype, 0,
MCA_COLL_BASE_TAG_REDUCE_SCATTER_BLOCK,
comm, MPI_STATUS_IGNORE));
if (MPI_SUCCESS != err) {
goto cleanup;
}
}
}
}
else {
/* get datatype information */
span = opal_datatype_span(&dtype->super, count, &gap);
if (0 == rank) {
/* temporary receive buffer. See coll_basic_reduce.c for
details on sizing */
recv_buf_free = (char*) malloc(span);
if (NULL == recv_buf_free) {
err = OMPI_ERR_OUT_OF_RESOURCE;
goto cleanup;
}
recv_buf = recv_buf_free - gap;
}
/* reduction */
err =
comm->c_coll->coll_reduce(sbuf, recv_buf, (int)count, dtype, op, 0,
comm, comm->c_coll->coll_reduce_module);
if (MPI_SUCCESS != err) {
goto cleanup;
}
/* scatter */
err = comm->c_coll->coll_scatter(recv_buf, rcount, dtype,
rbuf, rcount, dtype, 0,
comm, comm->c_coll->coll_scatter_module);
}
cleanup:
if (NULL != recv_buf_free) free(recv_buf_free);
return err;
}
/*
* ompi_coll_base_reduce_scatter_block_intra_recursivedoubling
*
* Function: Recursive doubling algorithm for reduce_scatter_block.
* Accepts: Same as MPI_Reduce_scatter_block
* Returns: MPI_SUCCESS or error code
*
* Description: Implements recursive doubling algorithm for MPI_Reduce_scatter_block.
* The algorithm preserves order of operations so it can
* be used both by commutative and non-commutative operations.
*
* Time complexity: \alpha\log(p) + \beta*m(\log(p)-(p-1)/p) + \gamma*m(\log(p)-(p-1)/p),
* where m = rcount * comm_size, p = comm_size
* Memory requirements (per process): 2 * rcount * comm_size * typesize
*/
int
ompi_coll_base_reduce_scatter_block_intra_recursivedoubling(
const void *sbuf, void *rbuf, int rcount, struct ompi_datatype_t *dtype,
struct ompi_op_t *op, struct ompi_communicator_t *comm,
mca_coll_base_module_t *module)
{
struct ompi_datatype_t *dtypesend = NULL, *dtyperecv = NULL;
char *tmprecv_raw = NULL, *tmpbuf_raw = NULL, *tmprecv, *tmpbuf;
ptrdiff_t span, gap, totalcount, extent;
int blocklens[2], displs[2];
int err = MPI_SUCCESS;
int comm_size = ompi_comm_size(comm);
int rank = ompi_comm_rank(comm);
OPAL_OUTPUT((ompi_coll_base_framework.framework_output,
"coll:base:reduce_scatter_block_intra_recursivedoubling: rank %d/%d",
rank, comm_size));
if (rcount == 0)
return MPI_SUCCESS;
if (comm_size < 2)
return MPI_SUCCESS;
totalcount = comm_size * (size_t)rcount;
if( OPAL_UNLIKELY(totalcount > INT_MAX) ) {
/*
* Large payload collectives are not supported by this algorithm.
* The blocklens and displs calculations in the loop below
* will overflow an int data type.
* Fallback to the linear algorithm.
*/
return ompi_coll_base_reduce_scatter_block_basic_linear(sbuf, rbuf, rcount, dtype, op, comm, module);
}
ompi_datatype_type_extent(dtype, &extent);
span = opal_datatype_span(&dtype->super, totalcount, &gap);
tmpbuf_raw = malloc(span);
tmprecv_raw = malloc(span);
if (NULL == tmpbuf_raw || NULL == tmprecv_raw) {
err = OMPI_ERR_OUT_OF_RESOURCE;
goto cleanup_and_return;
}
tmpbuf = tmpbuf_raw - gap;
tmprecv = tmprecv_raw - gap;
if (sbuf != MPI_IN_PLACE) {
err = ompi_datatype_copy_content_same_ddt(dtype, totalcount, tmpbuf, (char *)sbuf);
if (MPI_SUCCESS != err) { goto cleanup_and_return; }
} else {
err = ompi_datatype_copy_content_same_ddt(dtype, totalcount, tmpbuf, rbuf);
if (MPI_SUCCESS != err) { goto cleanup_and_return; }
}
int is_commutative = ompi_op_is_commute(op);
/* Recursive distance doubling */
for (int mask = 1; mask < comm_size; mask <<= 1) {
int remote = rank ^ mask;
int cur_tree_root = ompi_rounddown(rank, mask);
int remote_tree_root = ompi_rounddown(remote, mask);
/*
* Let be m is a block size in bytes (rcount), p is a comm_size,
* p*m is a total message size in sbuf.
* Step 1: processes send and recv (p*m-m) amount of data
* Step 2: processes send and recv (p*m-2*m) amount of data
* Step 3: processes send and recv (p*m-4*m) amount of data
* ...
* Step ceil(\log_2(p)): send and recv (p*m-m*2^floor{\log_2(p-1)})
*
* Send block from tmpbuf: [0..cur_tree_root - 1], [cur_tree_root + mask, p - 1]
* Recv block into tmprecv: [0..remote_tree_root - 1], [remote_tree_root + mask, p - 1]
*/
/* Send type */
blocklens[0] = rcount * cur_tree_root;
blocklens[1] = (comm_size >= cur_tree_root + mask) ?
rcount * (comm_size - cur_tree_root - mask) : 0;
displs[0] = 0;
displs[1] = comm_size * rcount - blocklens[1];
err = ompi_datatype_create_indexed(2, blocklens, displs, dtype, &dtypesend);
if (MPI_SUCCESS != err) { goto cleanup_and_return; }
err = ompi_datatype_commit(&dtypesend);
if (MPI_SUCCESS != err) { goto cleanup_and_return; }
/* Recv type */
blocklens[0] = rcount * remote_tree_root;
blocklens[1] = (comm_size >= remote_tree_root + mask) ?
rcount * (comm_size - remote_tree_root - mask) : 0;
displs[0] = 0;
displs[1] = comm_size * rcount - blocklens[1];
err = ompi_datatype_create_indexed(2, blocklens, displs, dtype, &dtyperecv);
if (MPI_SUCCESS != err) { goto cleanup_and_return; }
err = ompi_datatype_commit(&dtyperecv);
if (MPI_SUCCESS != err) { goto cleanup_and_return; }
int is_block_received = 0;
if (remote < comm_size) {
err = ompi_coll_base_sendrecv(tmpbuf, 1, dtypesend, remote,
MCA_COLL_BASE_TAG_REDUCE_SCATTER_BLOCK,
tmprecv, 1, dtyperecv, remote,
MCA_COLL_BASE_TAG_REDUCE_SCATTER_BLOCK,
comm, MPI_STATUS_IGNORE, rank);
if (MPI_SUCCESS != err) { goto cleanup_and_return; }
is_block_received = 1;
}
/*
* Non-power-of-two case: if process did not have destination process
* to communicate with, we need to send him the current result.
* Recursive halving algorithm is used for search of process.
*/
if (remote_tree_root + mask > comm_size) {
/*
* Compute the number of processes in current subtree
* that have all the data
*/
int nprocs_alldata = comm_size - cur_tree_root - mask;
for (int rhalving_mask = mask >> 1; rhalving_mask > 0; rhalving_mask >>= 1) {
remote = rank ^ rhalving_mask;
int tree_root = ompi_rounddown(rank, rhalving_mask << 1);
/*
* Send only if:
* 1) current process has data: (remote > rank) && (rank < tree_root + nprocs_alldata)
* 2) remote process does not have data at any step: remote >= tree_root + nprocs_alldata
*/
if ((remote > rank) && (rank < tree_root + nprocs_alldata)
&& (remote >= tree_root + nprocs_alldata)) {
err = MCA_PML_CALL(send(tmprecv, 1, dtyperecv, remote,
MCA_COLL_BASE_TAG_REDUCE_SCATTER_BLOCK,
MCA_PML_BASE_SEND_STANDARD, comm));
if (MPI_SUCCESS != err) { goto cleanup_and_return; }
} else if ((remote < rank) && (remote < tree_root + nprocs_alldata) &&
(rank >= tree_root + nprocs_alldata)) {
err = MCA_PML_CALL(recv(tmprecv, 1, dtyperecv, remote,
MCA_COLL_BASE_TAG_REDUCE_SCATTER_BLOCK,
comm, MPI_STATUS_IGNORE));
if (MPI_SUCCESS != err) { goto cleanup_and_return; }
is_block_received = 1;
}
}
}
if (is_block_received) {
/* After reduction the result must be in tmpbuf */
if (is_commutative || (remote_tree_root < cur_tree_root)) {
ompi_op_reduce(op, tmprecv, tmpbuf, blocklens[0], dtype);
ompi_op_reduce(op, tmprecv + (ptrdiff_t)displs[1] * extent,
tmpbuf + (ptrdiff_t)displs[1] * extent,
blocklens[1], dtype);
} else {
ompi_op_reduce(op, tmpbuf, tmprecv, blocklens[0], dtype);
ompi_op_reduce(op, tmpbuf + (ptrdiff_t)displs[1] * extent,
tmprecv + (ptrdiff_t)displs[1] * extent,
blocklens[1], dtype);
err = ompi_datatype_copy_content_same_ddt(dtyperecv, 1,
tmpbuf, tmprecv);
if (MPI_SUCCESS != err) { goto cleanup_and_return; }
}
}
err = ompi_datatype_destroy(&dtypesend);
if (MPI_SUCCESS != err) { goto cleanup_and_return; }
err = ompi_datatype_destroy(&dtyperecv);
if (MPI_SUCCESS != err) { goto cleanup_and_return; }
}
err = ompi_datatype_copy_content_same_ddt(dtype, rcount, rbuf,
tmpbuf + (ptrdiff_t)rank * rcount * extent);
if (MPI_SUCCESS != err) { goto cleanup_and_return; }
cleanup_and_return:
if (dtypesend)
ompi_datatype_destroy(&dtypesend);
if (dtyperecv)
ompi_datatype_destroy(&dtyperecv);
if (tmpbuf_raw)
free(tmpbuf_raw);
if (tmprecv_raw)
free(tmprecv_raw);
return err;
}
/*
* ompi_range_sum: Returns sum of elems in intersection of [a, b] and [0, r]
* index: 0 1 2 3 4 ... r r+1 r+2 ... nproc_pof2
* value: 2 2 2 2 2 ... 2 1 1 ... 1
*/
static int ompi_range_sum(int a, int b, int r)
{
if (r < a)
return b - a + 1;
else if (r > b)
return 2 * (b - a + 1);
return 2 * (r - a + 1) + b - r;
}
/*
* ompi_coll_base_reduce_scatter_block_intra_recursivehalving
*
* Function: Recursive halving algorithm for reduce_scatter_block
* Accepts: Same as MPI_Reduce_scatter_block
* Returns: MPI_SUCCESS or error code
*
* Description: Implements recursive halving algorithm for MPI_Reduce_scatter_block.
* The algorithm can be used by commutative operations only.
*
* Limitations: commutative operations only
* Memory requirements (per process): 2 * rcount * comm_size * typesize
*/
int
ompi_coll_base_reduce_scatter_block_intra_recursivehalving(
const void *sbuf, void *rbuf, int rcount, struct ompi_datatype_t *dtype,
struct ompi_op_t *op, struct ompi_communicator_t *comm,
mca_coll_base_module_t *module)
{
char *tmprecv_raw = NULL, *tmpbuf_raw = NULL, *tmprecv, *tmpbuf;
ptrdiff_t span, gap, totalcount, extent;
int err = MPI_SUCCESS;
int comm_size = ompi_comm_size(comm);
int rank = ompi_comm_rank(comm);
OPAL_OUTPUT((ompi_coll_base_framework.framework_output,
"coll:base:reduce_scatter_block_intra_recursivehalving: rank %d/%d",
rank, comm_size));
if (rcount == 0 || comm_size < 2)
return MPI_SUCCESS;
if (!ompi_op_is_commute(op)) {
OPAL_OUTPUT((ompi_coll_base_framework.framework_output,
"coll:base:reduce_scatter_block_intra_recursivehalving: rank %d/%d "
"switching to basic reduce_scatter_block", rank, comm_size));
return ompi_coll_base_reduce_scatter_block_basic_linear(sbuf, rbuf, rcount, dtype,
op, comm, module);
}
totalcount = comm_size * (size_t)rcount;
ompi_datatype_type_extent(dtype, &extent);
span = opal_datatype_span(&dtype->super, totalcount, &gap);
tmpbuf_raw = malloc(span);
tmprecv_raw = malloc(span);
if (NULL == tmpbuf_raw || NULL == tmprecv_raw) {
err = OMPI_ERR_OUT_OF_RESOURCE;
goto cleanup_and_return;
}
tmpbuf = tmpbuf_raw - gap;
tmprecv = tmprecv_raw - gap;
if (sbuf != MPI_IN_PLACE) {
err = ompi_datatype_copy_content_same_ddt(dtype, totalcount, tmpbuf, (char *)sbuf);
if (MPI_SUCCESS != err) { goto cleanup_and_return; }
} else {
err = ompi_datatype_copy_content_same_ddt(dtype, totalcount, tmpbuf, rbuf);
if (MPI_SUCCESS != err) { goto cleanup_and_return; }
}
/*
* Step 1. Reduce the number of processes to the nearest lower power of two
* p' = 2^{\floor{\log_2 p}} by removing r = p - p' processes.
* In the first 2r processes (ranks 0 to 2r - 1), all the even ranks send
* the input vector to their neighbor (rank + 1) and all the odd ranks recv
* the input vector and perform local reduction.
* The odd ranks (0 to 2r - 1) contain the reduction with the input
* vector on their neighbors (the even ranks). The first r odd
* processes and the p - 2r last processes are renumbered from
* 0 to 2^{\floor{\log_2 p}} - 1. Even ranks do not participate in the
* rest of the algorithm.
*/
/* Find nearest power-of-two less than or equal to comm_size */
int nprocs_pof2 = opal_next_poweroftwo(comm_size);
nprocs_pof2 >>= 1;
int nprocs_rem = comm_size - nprocs_pof2;
int vrank = -1;
if (rank < 2 * nprocs_rem) {
if ((rank % 2) == 0) {
/* Even process */
err = MCA_PML_CALL(send(tmpbuf, totalcount, dtype, rank + 1,
MCA_COLL_BASE_TAG_REDUCE_SCATTER_BLOCK,
MCA_PML_BASE_SEND_STANDARD, comm));
if (OMPI_SUCCESS != err) { goto cleanup_and_return; }
/* This process does not pariticipate in the rest of the algorithm */
vrank = -1;
} else {
/* Odd process */
err = MCA_PML_CALL(recv(tmprecv, totalcount, dtype, rank - 1,
MCA_COLL_BASE_TAG_REDUCE_SCATTER_BLOCK,
comm, MPI_STATUS_IGNORE));
if (OMPI_SUCCESS != err) { goto cleanup_and_return; }
ompi_op_reduce(op, tmprecv, tmpbuf, totalcount, dtype);
/* Adjust rank to be the bottom "remain" ranks */
vrank = rank / 2;
}
} else {
/* Adjust rank to show that the bottom "even remain" ranks dropped out */
vrank = rank - nprocs_rem;
}
if (vrank != -1) {
/*
* Step 2. Recursive vector halving. We have p' = 2^{\floor{\log_2 p}}
* power-of-two number of processes with new ranks (vrank) and partial
* result in tmpbuf.
* All processes then compute the reduction between the local
* buffer and the received buffer. In the next \log_2(p') - 1 steps, the
* buffers are recursively halved. At the end, each of the p' processes
* has 1 / p' of the total reduction result.
*/
int send_index = 0, recv_index = 0, last_index = nprocs_pof2;
for (int mask = nprocs_pof2 >> 1; mask > 0; mask >>= 1) {
int vpeer = vrank ^ mask;
int peer = (vpeer < nprocs_rem) ? vpeer * 2 + 1 : vpeer + nprocs_rem;
/*
* Calculate the recv_count and send_count because the
* even-numbered processes who no longer participate will
* have their result calculated by the process to their
* right (rank + 1).
*/
size_t send_count = 0, recv_count = 0;
if (vrank < vpeer) {
/* Send the right half of the buffer, recv the left half */
send_index = recv_index + mask;
send_count = rcount * (size_t)ompi_range_sum(send_index, last_index - 1, nprocs_rem - 1);
recv_count = rcount * (size_t)ompi_range_sum(recv_index, send_index - 1, nprocs_rem - 1);
} else {
/* Send the left half of the buffer, recv the right half */
recv_index = send_index + mask;
send_count = rcount * (size_t)ompi_range_sum(send_index, recv_index - 1, nprocs_rem - 1);
recv_count = rcount * (size_t)ompi_range_sum(recv_index, last_index - 1, nprocs_rem - 1);
}
ptrdiff_t rdispl = rcount * (size_t)((recv_index <= nprocs_rem - 1) ?
2 * recv_index : nprocs_rem + recv_index);
ptrdiff_t sdispl = rcount * (size_t)((send_index <= nprocs_rem - 1) ?
2 * send_index : nprocs_rem + send_index);
struct ompi_request_t *request = NULL;
if (recv_count > 0) {
err = MCA_PML_CALL(irecv(tmprecv + rdispl * extent, recv_count,
dtype, peer, MCA_COLL_BASE_TAG_REDUCE_SCATTER_BLOCK,
comm, &request));
if (OMPI_SUCCESS != err) { goto cleanup_and_return; }
}
if (send_count > 0) {
err = MCA_PML_CALL(send(tmpbuf + sdispl * extent, send_count,
dtype, peer, MCA_COLL_BASE_TAG_REDUCE_SCATTER_BLOCK,
MCA_PML_BASE_SEND_STANDARD,
comm));
if (OMPI_SUCCESS != err) { goto cleanup_and_return; }
}
if (recv_count > 0) {
err = ompi_request_wait(&request, MPI_STATUS_IGNORE);
if (OMPI_SUCCESS != err) { goto cleanup_and_return; }
ompi_op_reduce(op, tmprecv + rdispl * extent,
tmpbuf + rdispl * extent, recv_count, dtype);
}
send_index = recv_index;
last_index = recv_index + mask;
}
err = ompi_datatype_copy_content_same_ddt(dtype, rcount, rbuf,
tmpbuf + (ptrdiff_t)rank * rcount * extent);
if (MPI_SUCCESS != err) { goto cleanup_and_return; }
}
/* Step 3. Send the result to excluded even ranks */
if (rank < 2 * nprocs_rem) {
if ((rank % 2) == 0) {
/* Even process */
err = MCA_PML_CALL(recv(rbuf, rcount, dtype, rank + 1,
MCA_COLL_BASE_TAG_REDUCE_SCATTER_BLOCK, comm,
MPI_STATUS_IGNORE));
if (OMPI_SUCCESS != err) { goto cleanup_and_return; }
} else {
/* Odd process */
err = MCA_PML_CALL(send(tmpbuf + (ptrdiff_t)(rank - 1) * rcount * extent,
rcount, dtype, rank - 1,
MCA_COLL_BASE_TAG_REDUCE_SCATTER_BLOCK,
MCA_PML_BASE_SEND_STANDARD, comm));
if (MPI_SUCCESS != err) { goto cleanup_and_return; }
}
}
cleanup_and_return:
if (tmpbuf_raw)
free(tmpbuf_raw);
if (tmprecv_raw)
free(tmprecv_raw);
return err;
}
static int ompi_coll_base_reduce_scatter_block_intra_butterfly_pof2(
const void *sbuf, void *rbuf, int rcount, struct ompi_datatype_t *dtype,
struct ompi_op_t *op, struct ompi_communicator_t *comm,
mca_coll_base_module_t *module);
/*
* ompi_coll_base_reduce_scatter_block_intra_butterfly
*
* Function: Butterfly algorithm for reduce_scatter_block
* Accepts: Same as MPI_Reduce_scatter_block
* Returns: MPI_SUCCESS or error code
*
* Description: Implements butterfly algorithm for MPI_Reduce_scatter_block [*].
* The algorithm can be used both by commutative and non-commutative
* operations, for power-of-two and non-power-of-two number of processes.
*
* [*] J.L. Traff. An improved Algorithm for (non-commutative) Reduce-scatter
* with an Application // Proc. of EuroPVM/MPI, 2005. -- pp. 129-137.
*
* Time complexity:
* m\lambda + (\alpha + m\beta + m\gamma) +
* + 2\log_2(p)\alpha + 2m(1-1/p)\beta + m(1-1/p)\gamma +
* + 3(\alpha + m/p\beta) = O(m\lambda + log(p)\alpha + m\beta + m\gamma),
* where m = rcount * comm_size, p = comm_size
* Memory requirements (per process): 2 * rcount * comm_size * typesize
*
* Example: comm_size=6, nprocs_pof2=4, nprocs_rem=2, rcount=1, sbuf=[0,1,...,5]
* Step 1. Reduce the number of processes to 4
* rank 0: [0|1|2|3|4|5]: send to 1: vrank -1
* rank 1: [0|1|2|3|4|5]: recv from 0, op: vrank 0: [0|2|4|6|8|10]
* rank 2: [0|1|2|3|4|5]: send to 3: vrank -1
* rank 3: [0|1|2|3|4|5]: recv from 2, op: vrank 1: [0|2|4|6|8|10]
* rank 4: [0|1|2|3|4|5]: vrank 2: [0|1|2|3|4|5]
* rank 5: [0|1|2|3|4|5]: vrank 3: [0|1|2|3|4|5]
*
* Step 2. Butterfly. Buffer of 6 elements is divided into 4 blocks.
* Round 1 (mask=1, nblocks=2)
* 0: vrank -1
* 1: vrank 0 [0 2|4 6|8|10]: exch with 1: send [2,3], recv [0,1]: [0 4|8 12|*|*]
* 2: vrank -1
* 3: vrank 1 [0 2|4 6|8|10]: exch with 0: send [0,1], recv [2,3]: [**|**|16|20]
* 4: vrank 2 [0 1|2 3|4|5] : exch with 3: send [2,3], recv [0,1]: [0 2|4 6|*|*]
* 5: vrank 3 [0 1|2 3|4|5] : exch with 2: send [0,1], recv [2,3]: [**|**|8|10]
*
* Round 2 (mask=2, nblocks=1)
* 0: vrank -1
* 1: vrank 0 [0 4|8 12|*|*]: exch with 2: send [1], recv [0]: [0 6|**|*|*]
* 2: vrank -1
* 3: vrank 1 [**|**|16|20] : exch with 3: send [3], recv [2]: [**|**|24|*]
* 4: vrank 2 [0 2|4 6|*|*] : exch with 0: send [0], recv [1]: [**|12 18|*|*]
* 5: vrank 3 [**|**|8|10] : exch with 1: send [2], recv [3]: [**|**|*|30]
*
* Step 3. Exchange with remote process according to a mirror permutation:
* mperm(0)=0, mperm(1)=2, mperm(2)=1, mperm(3)=3
* 0: vrank -1: recv "0" from process 0
* 1: vrank 0 [0 6|**|*|*]: send "0" to 0, copy "6" to rbuf (mperm(0)=0)
* 2: vrank -1: recv result "12" from process 4
* 3: vrank 1 [**|**|24|*]
* 4: vrank 2 [**|12 18|*|*]: send "12" to 2, send "18" to 3, recv "24" from 3
* 5: vrank 3 [**|**|*|30]: copy "30" to rbuf (mperm(3)=3)
*/
int
ompi_coll_base_reduce_scatter_block_intra_butterfly(
const void *sbuf, void *rbuf, int rcount, struct ompi_datatype_t *dtype,
struct ompi_op_t *op, struct ompi_communicator_t *comm,
mca_coll_base_module_t *module)
{
char *tmpbuf[2] = {NULL, NULL}, *psend, *precv;
ptrdiff_t span, gap, totalcount, extent;
int err = MPI_SUCCESS;
int comm_size = ompi_comm_size(comm);
int rank = ompi_comm_rank(comm);
OPAL_OUTPUT((ompi_coll_base_framework.framework_output,
"coll:base:reduce_scatter_block_intra_butterfly: rank %d/%d",
rank, comm_size));
if (rcount == 0 || comm_size < 2)
return MPI_SUCCESS;
if (!(comm_size & (comm_size - 1))) {
/* Special case: comm_size is a power of two */
return ompi_coll_base_reduce_scatter_block_intra_butterfly_pof2(
sbuf, rbuf, rcount, dtype, op, comm, module);
}
totalcount = comm_size * (size_t)rcount;
ompi_datatype_type_extent(dtype, &extent);
span = opal_datatype_span(&dtype->super, totalcount, &gap);
tmpbuf[0] = malloc(span);
tmpbuf[1] = malloc(span);
if (NULL == tmpbuf[0] || NULL == tmpbuf[1]) {
err = OMPI_ERR_OUT_OF_RESOURCE;
goto cleanup_and_return;
}
psend = tmpbuf[0] - gap;
precv = tmpbuf[1] - gap;
if (sbuf != MPI_IN_PLACE) {
err = ompi_datatype_copy_content_same_ddt(dtype, totalcount, psend, (char *)sbuf);
if (MPI_SUCCESS != err) { goto cleanup_and_return; }
} else {
err = ompi_datatype_copy_content_same_ddt(dtype, totalcount, psend, rbuf);
if (MPI_SUCCESS != err) { goto cleanup_and_return; }
}
/*
* Step 1. Reduce the number of processes to the nearest lower power of two
* p' = 2^{\floor{\log_2 p}} by removing r = p - p' processes.
* In the first 2r processes (ranks 0 to 2r - 1), all the even ranks send
* the input vector to their neighbor (rank + 1) and all the odd ranks recv
* the input vector and perform local reduction.
* The odd ranks (0 to 2r - 1) contain the reduction with the input
* vector on their neighbors (the even ranks). The first r odd
* processes and the p - 2r last processes are renumbered from
* 0 to 2^{\floor{\log_2 p}} - 1. Even ranks do not participate in the
* rest of the algorithm.
*/
/* Find nearest power-of-two less than or equal to comm_size */
int nprocs_pof2 = opal_next_poweroftwo(comm_size);
nprocs_pof2 >>= 1;
int nprocs_rem = comm_size - nprocs_pof2;
int log2_size = opal_cube_dim(nprocs_pof2);
int vrank = -1;
if (rank < 2 * nprocs_rem) {
if ((rank % 2) == 0) {
/* Even process */
err = MCA_PML_CALL(send(psend, totalcount, dtype, rank + 1,
MCA_COLL_BASE_TAG_REDUCE_SCATTER_BLOCK,
MCA_PML_BASE_SEND_STANDARD, comm));
if (OMPI_SUCCESS != err) { goto cleanup_and_return; }
/* This process does not participate in the rest of the algorithm */
vrank = -1;
} else {
/* Odd process */
err = MCA_PML_CALL(recv(precv, totalcount, dtype, rank - 1,
MCA_COLL_BASE_TAG_REDUCE_SCATTER_BLOCK,
comm, MPI_STATUS_IGNORE));
if (OMPI_SUCCESS != err) { goto cleanup_and_return; }
ompi_op_reduce(op, precv, psend, totalcount, dtype);
/* Adjust rank to be the bottom "remain" ranks */
vrank = rank / 2;
}
} else {
/* Adjust rank to show that the bottom "even remain" ranks dropped out */
vrank = rank - nprocs_rem;
}
if (vrank != -1) {
/*
* Now, psend vector of size rcount * comm_size elements is divided into
* nprocs_pof2 blocks:
* block 0 has 2*rcount elems (for process 0 and 1)
* block 1 has 2*rcount elems (for process 2 and 3)
* ...
* block r-1 has 2*rcount elems (for process 2*(r-1) and 2*(r-1)+1)
* block r has rcount elems (for process r+r)
* block r+1 has rcount elems (for process r+r+1)
* ...
* block nprocs_pof2 - 1 has rcount elems (for process r + nprocs_pof2-1)
*/
int nblocks = nprocs_pof2, send_index = 0, recv_index = 0;
for (int mask = 1; mask < nprocs_pof2; mask <<= 1) {
int vpeer = vrank ^ mask;
int peer = (vpeer < nprocs_rem) ? vpeer * 2 + 1 : vpeer + nprocs_rem;
nblocks /= 2;
if ((vrank & mask) == 0) {
/* Send the upper half of reduction buffer, recv the lower half */
send_index += nblocks;
} else {
/* Send the upper half of reduction buffer, recv the lower half */
recv_index += nblocks;
}
size_t send_count = rcount *
(size_t)ompi_range_sum(send_index,
send_index + nblocks - 1,
nprocs_rem - 1);
size_t recv_count = rcount *
(size_t)ompi_range_sum(recv_index,
recv_index + nblocks - 1,
nprocs_rem - 1);
ptrdiff_t sdispl = rcount * (size_t)((send_index <= nprocs_rem - 1) ?
2 * send_index : nprocs_rem + send_index);
ptrdiff_t rdispl = rcount * (size_t)((recv_index <= nprocs_rem - 1) ?
2 * recv_index : nprocs_rem + recv_index);
err = ompi_coll_base_sendrecv(psend + (ptrdiff_t)sdispl * extent, send_count,
dtype, peer, MCA_COLL_BASE_TAG_REDUCE_SCATTER_BLOCK,
precv + (ptrdiff_t)rdispl * extent, recv_count,
dtype, peer, MCA_COLL_BASE_TAG_REDUCE_SCATTER_BLOCK,
comm, MPI_STATUS_IGNORE, rank);
if (MPI_SUCCESS != err) { goto cleanup_and_return; }
if (vrank < vpeer) {
/* precv = psend <op> precv */
ompi_op_reduce(op, psend + (ptrdiff_t)rdispl * extent,
precv + (ptrdiff_t)rdispl * extent, recv_count, dtype);
char *p = psend;
psend = precv;
precv = p;
} else {
/* psend = precv <op> psend */
ompi_op_reduce(op, precv + (ptrdiff_t)rdispl * extent,
psend + (ptrdiff_t)rdispl * extent, recv_count, dtype);
}
send_index = recv_index;
}
/*
* psend points to the result: [send_index, send_index + recv_count - 1]
* Exchange results with remote process according to a mirror permutation.
*/
int vpeer = ompi_mirror_perm(vrank, log2_size);
int peer = (vpeer < nprocs_rem) ? vpeer * 2 + 1 : vpeer + nprocs_rem;
if (vpeer < nprocs_rem) {
/*
* Process has two blocks: for excluded process and own.
* Send result to the excluded process.
*/
ptrdiff_t sdispl = rcount * (size_t)((send_index <= nprocs_rem - 1) ?
2 * send_index : nprocs_rem + send_index);
err = MCA_PML_CALL(send(psend + (ptrdiff_t)sdispl * extent,
rcount, dtype, peer - 1,
MCA_COLL_BASE_TAG_REDUCE_SCATTER_BLOCK,
MCA_PML_BASE_SEND_STANDARD, comm));
if (MPI_SUCCESS != err) { goto cleanup_and_return; }
}
/* Send result to a remote process according to a mirror permutation */
ptrdiff_t sdispl = rcount * (size_t)((send_index <= nprocs_rem - 1) ?
2 * send_index : nprocs_rem + send_index);
/* If process has two blocks, then send the second block (own block) */
if (vpeer < nprocs_rem)
sdispl += rcount;
if (vpeer != vrank) {
err = ompi_coll_base_sendrecv(psend + (ptrdiff_t)sdispl * extent, rcount,
dtype, peer, MCA_COLL_BASE_TAG_REDUCE_SCATTER_BLOCK,
rbuf, rcount, dtype, peer,
MCA_COLL_BASE_TAG_REDUCE_SCATTER_BLOCK,
comm, MPI_STATUS_IGNORE, rank);
if (MPI_SUCCESS != err) { goto cleanup_and_return; }
} else {
err = ompi_datatype_copy_content_same_ddt(dtype, rcount, rbuf,
psend + (ptrdiff_t)sdispl * extent);
if (MPI_SUCCESS != err) { goto cleanup_and_return; }
}
} else {
/* Excluded process: receive result */
int vpeer = ompi_mirror_perm((rank + 1) / 2, log2_size);
int peer = (vpeer < nprocs_rem) ? vpeer * 2 + 1 : vpeer + nprocs_rem;
err = MCA_PML_CALL(recv(rbuf, rcount, dtype, peer,
MCA_COLL_BASE_TAG_REDUCE_SCATTER_BLOCK, comm,
MPI_STATUS_IGNORE));
if (OMPI_SUCCESS != err) { goto cleanup_and_return; }
}
cleanup_and_return:
if (tmpbuf[0])
free(tmpbuf[0]);
if (tmpbuf[1])
free(tmpbuf[1]);
return err;
}
/*
* ompi_coll_base_reduce_scatter_block_intra_butterfly_pof2
*
* Function: Butterfly algorithm for reduce_scatter_block
* Accepts: Same as MPI_Reduce_scatter_block
* Returns: MPI_SUCCESS or error code
* Limitations: Power-of-two number of processes.
*
* Description: Implements butterfly algorithm for MPI_Reduce_scatter_block [*].
* The algorithm can be used both by commutative and non-commutative
* operations, for power-of-two number of processes.
*
* [*] J.L. Traff. An improved Algorithm for (non-commutative) Reduce-scatter
* with an Application // Proc. of EuroPVM/MPI, 2005. -- pp. 129-137.
*
* Time complexity:
* m\lambda + 2\log_2(p)\alpha + 2m(1-1/p)\beta + m(1-1/p)\gamma + m/p\lambda =
* = O(m\lambda + log(p)\alpha + m\beta + m\gamma),
* where m = rcount * comm_size, p = comm_size
* Memory requirements (per process): 2 * rcount * comm_size * typesize
*
* Example: comm_size=4, rcount=1, sbuf=[0,1,2,3]
* Step 1. Permute the blocks according to a mirror permutation:
* mperm(0)=0, mperm(1)=2, mperm(2)=1, mperm(3)=3
* sbuf=[0|1|2|3] ==> psend=[0|2|1|3]
*
* Step 2. Butterfly
* Round 1 (mask=1, nblocks=2)
* 0: [0|2|1|3]: exch with 1: send [2,3], recv [0,1]: [0|4|*|*]
* 1: [0|2|1|3]: exch with 0: send [0,1], recv [2,3]: [*|*|2|6]
* 2: [0|2|1|3]: exch with 3: send [2,3], recv [0,1]: [0|4|*|*]
* 3: [0|2|1|3]: exch with 2: send [0,1], recv [2,3]: [*|*|2|6]
*
* Round 2 (mask=2, nblocks=1)
* 0: [0|4|*|*]: exch with 2: send [1], recv [0]: [0|*|*|*]
* 1: [*|*|2|6]: exch with 3: send [3], recv [2]: [*|*|4|*]
* 2: [0|4|*|*]: exch with 0: send [0], recv [1]: [*|8|*|*]
* 3: [*|*|2|6]: exch with 1: send [2], recv [3]: [*|*|*|12]
*
* Step 3. Copy result to rbuf
*/
static int
ompi_coll_base_reduce_scatter_block_intra_butterfly_pof2(
const void *sbuf, void *rbuf, int rcount, struct ompi_datatype_t *dtype,
struct ompi_op_t *op, struct ompi_communicator_t *comm,
mca_coll_base_module_t *module)
{
char *tmpbuf[2] = {NULL, NULL}, *psend, *precv;
ptrdiff_t span, gap, totalcount, extent;
int err = MPI_SUCCESS;
int comm_size = ompi_comm_size(comm);
int rank = ompi_comm_rank(comm);
if (rcount == 0 || comm_size < 2)
return MPI_SUCCESS;
totalcount = comm_size * (size_t)rcount;
ompi_datatype_type_extent(dtype, &extent);
span = opal_datatype_span(&dtype->super, totalcount, &gap);
tmpbuf[0] = malloc(span);
tmpbuf[1] = malloc(span);
if (NULL == tmpbuf[0] || NULL == tmpbuf[1]) {
err = OMPI_ERR_OUT_OF_RESOURCE;
goto cleanup_and_return;
}
psend = tmpbuf[0] - gap;
precv = tmpbuf[1] - gap;
/* Permute the blocks according to a mirror permutation */
int log2_comm_size = opal_cube_dim(comm_size);
char *pdata = (sbuf != MPI_IN_PLACE) ? (char *)sbuf : rbuf;
for (int i = 0; i < comm_size; i++) {
char *src = pdata + (ptrdiff_t)i * extent * rcount;
char *dst = psend + (ptrdiff_t)ompi_mirror_perm(i, log2_comm_size) * extent * rcount;
err = ompi_datatype_copy_content_same_ddt(dtype, rcount, dst, src);
if (MPI_SUCCESS != err) { goto cleanup_and_return; }
}
size_t nblocks = totalcount, send_index = 0, recv_index = 0;
for (int mask = 1; mask < comm_size; mask <<= 1) {
int peer = rank ^ mask;
nblocks /= 2;
if ((rank & mask) == 0) {
/* Send the upper half of reduction buffer, recv the lower half */
send_index += nblocks;
} else {
/* Send the upper half of reduction buffer, recv the lower half */
recv_index += nblocks;
}
err = ompi_coll_base_sendrecv(psend + (ptrdiff_t)send_index * extent,
nblocks, dtype, peer,
MCA_COLL_BASE_TAG_REDUCE_SCATTER_BLOCK,
precv + (ptrdiff_t)recv_index * extent,
nblocks, dtype, peer,
MCA_COLL_BASE_TAG_REDUCE_SCATTER_BLOCK,
comm, MPI_STATUS_IGNORE, rank);
if (MPI_SUCCESS != err) { goto cleanup_and_return; }
if (rank < peer) {
/* precv = psend <op> precv */
ompi_op_reduce(op, psend + (ptrdiff_t)recv_index * extent,
precv + (ptrdiff_t)recv_index * extent, nblocks, dtype);
char *p = psend;
psend = precv;
precv = p;
} else {
/* psend = precv <op> psend */
ompi_op_reduce(op, precv + (ptrdiff_t)recv_index * extent,
psend + (ptrdiff_t)recv_index * extent, nblocks, dtype);
}
send_index = recv_index;
}
/* Copy the result to the rbuf */
err = ompi_datatype_copy_content_same_ddt(dtype, rcount, rbuf,
psend + (ptrdiff_t)recv_index * extent);
if (MPI_SUCCESS != err) { goto cleanup_and_return; }
cleanup_and_return:
if (tmpbuf[0])
free(tmpbuf[0]);
if (tmpbuf[1])
free(tmpbuf[1]);
return err;
}