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openmpi/ompi/mca/coll/base/coll_base_reduce.c
2015-02-26 15:52:00 -05:00

829 строки
35 KiB
C

/* -*- 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) 2004-2015 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) 2013 Los Alamos National Security, LLC. All Rights
* reserved.
* Copyright (c) 2015 Research Organization for Information Science
* and Technology (RIST). All rights reserved.
* $COPYRIGHT$
*
* Additional copyrights may follow
*
* $HEADER$
*/
#include "ompi_config.h"
#include "mpi.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/base/coll_tags.h"
#include "ompi/mca/pml/pml.h"
#include "ompi/op/op.h"
#include "ompi/mca/coll/base/coll_base_functions.h"
#include "coll_base_topo.h"
/**
* This is a generic implementation of the reduce protocol. It used the tree
* provided as an argument and execute all operations using a segment of
* count times a datatype.
* For the last communication it will update the count in order to limit
* the number of datatype to the original count (original_count)
*
* Note that for non-commutative operations we cannot save memory copy
* for the first block: thus we must copy sendbuf to accumbuf on intermediate
* to keep the optimized loop happy.
*/
int ompi_coll_base_reduce_generic( void* sendbuf, void* recvbuf, int original_count,
ompi_datatype_t* datatype, ompi_op_t* op,
int root, ompi_communicator_t* comm,
mca_coll_base_module_t *module,
ompi_coll_tree_t* tree, int count_by_segment,
int max_outstanding_reqs )
{
char *inbuf[2] = {NULL, NULL}, *inbuf_free[2] = {NULL, NULL};
char *accumbuf = NULL, *accumbuf_free = NULL;
char *local_op_buffer = NULL, *sendtmpbuf = NULL;
ptrdiff_t extent, lower_bound, segment_increment;
size_t typelng;
ompi_request_t* reqs[2] = {MPI_REQUEST_NULL, MPI_REQUEST_NULL};
int num_segments, line, ret, segindex, i, rank;
int recvcount, prevcount, inbi;
/**
* Determine number of segments and number of elements
* sent per operation
*/
ompi_datatype_get_extent( datatype, &lower_bound, &extent );
ompi_datatype_type_size( datatype, &typelng );
num_segments = (original_count + count_by_segment - 1) / count_by_segment;
segment_increment = (ptrdiff_t)count_by_segment * extent;
sendtmpbuf = (char*) sendbuf;
if( sendbuf == MPI_IN_PLACE ) {
sendtmpbuf = (char *)recvbuf;
}
OPAL_OUTPUT((ompi_coll_base_framework.framework_output, "coll:base:reduce_generic count %d, msg size %ld, segsize %ld, max_requests %d",
original_count, (unsigned long)((ptrdiff_t)num_segments * (ptrdiff_t)segment_increment),
(unsigned long)segment_increment, max_outstanding_reqs));
rank = ompi_comm_rank(comm);
/* non-leaf nodes - wait for children to send me data & forward up
(if needed) */
if( tree->tree_nextsize > 0 ) {
ptrdiff_t true_lower_bound, true_extent, real_segment_size;
ompi_datatype_get_true_extent( datatype, &true_lower_bound,
&true_extent );
/* handle non existant recv buffer (i.e. its NULL) and
protect the recv buffer on non-root nodes */
accumbuf = (char*)recvbuf;
if( (NULL == accumbuf) || (root != rank) ) {
/* Allocate temporary accumulator buffer. */
accumbuf_free = (char*)malloc(true_extent +
(ptrdiff_t)(original_count - 1) * extent);
if (accumbuf_free == NULL) {
line = __LINE__; ret = -1; goto error_hndl;
}
accumbuf = accumbuf_free - lower_bound;
}
/* If this is a non-commutative operation we must copy
sendbuf to the accumbuf, in order to simplfy the loops */
if (!ompi_op_is_commute(op)) {
ompi_datatype_copy_content_same_ddt(datatype, original_count,
(char*)accumbuf,
(char*)sendtmpbuf);
}
/* Allocate two buffers for incoming segments */
real_segment_size = true_extent + (ptrdiff_t)(count_by_segment - 1) * extent;
inbuf_free[0] = (char*) malloc(real_segment_size);
if( inbuf_free[0] == NULL ) {
line = __LINE__; ret = -1; goto error_hndl;
}
inbuf[0] = inbuf_free[0] - lower_bound;
/* if there is chance to overlap communication -
allocate second buffer */
if( (num_segments > 1) || (tree->tree_nextsize > 1) ) {
inbuf_free[1] = (char*) malloc(real_segment_size);
if( inbuf_free[1] == NULL ) {
line = __LINE__; ret = -1; goto error_hndl;
}
inbuf[1] = inbuf_free[1] - lower_bound;
}
/* reset input buffer index and receive count */
inbi = 0;
recvcount = 0;
/* for each segment */
for( segindex = 0; segindex <= num_segments; segindex++ ) {
prevcount = recvcount;
/* recvcount - number of elements in current segment */
recvcount = count_by_segment;
if( segindex == (num_segments-1) )
recvcount = original_count - (ptrdiff_t)count_by_segment * (ptrdiff_t)segindex;
/* for each child */
for( i = 0; i < tree->tree_nextsize; i++ ) {
/**
* We try to overlap communication:
* either with next segment or with the next child
*/
/* post irecv for current segindex on current child */
if( segindex < num_segments ) {
void* local_recvbuf = inbuf[inbi];
if( 0 == i ) {
/* for the first step (1st child per segment) and
* commutative operations we might be able to irecv
* directly into the accumulate buffer so that we can
* reduce(op) this with our sendbuf in one step as
* ompi_op_reduce only has two buffer pointers,
* this avoids an extra memory copy.
*
* BUT if the operation is non-commutative or
* we are root and are USING MPI_IN_PLACE this is wrong!
*/
if( (ompi_op_is_commute(op)) &&
!((MPI_IN_PLACE == sendbuf) && (rank == tree->tree_root)) ) {
local_recvbuf = accumbuf + (ptrdiff_t)segindex * (ptrdiff_t)segment_increment;
}
}
ret = MCA_PML_CALL(irecv(local_recvbuf, recvcount, datatype,
tree->tree_next[i],
MCA_COLL_BASE_TAG_REDUCE, comm,
&reqs[inbi]));
if (ret != MPI_SUCCESS) { line = __LINE__; goto error_hndl;}
}
/* wait for previous req to complete, if any.
if there are no requests reqs[inbi ^1] will be
MPI_REQUEST_NULL. */
/* wait on data from last child for previous segment */
ret = ompi_request_wait_all( 1, &reqs[inbi ^ 1],
MPI_STATUSES_IGNORE );
if (ret != MPI_SUCCESS) { line = __LINE__; goto error_hndl; }
local_op_buffer = inbuf[inbi ^ 1];
if( i > 0 ) {
/* our first operation is to combine our own [sendbuf] data
* with the data we recvd from down stream (but only
* the operation is commutative and if we are not root and
* not using MPI_IN_PLACE)
*/
if( 1 == i ) {
if( (ompi_op_is_commute(op)) &&
!((MPI_IN_PLACE == sendbuf) && (rank == tree->tree_root)) ) {
local_op_buffer = sendtmpbuf + (ptrdiff_t)segindex * (ptrdiff_t)segment_increment;
}
}
/* apply operation */
ompi_op_reduce(op, local_op_buffer,
accumbuf + (ptrdiff_t)segindex * (ptrdiff_t)segment_increment,
recvcount, datatype );
} else if ( segindex > 0 ) {
void* accumulator = accumbuf + (ptrdiff_t)(segindex-1) * (ptrdiff_t)segment_increment;
if( tree->tree_nextsize <= 1 ) {
if( (ompi_op_is_commute(op)) &&
!((MPI_IN_PLACE == sendbuf) && (rank == tree->tree_root)) ) {
local_op_buffer = sendtmpbuf + (ptrdiff_t)(segindex-1) * (ptrdiff_t)segment_increment;
}
}
ompi_op_reduce(op, local_op_buffer, accumulator, prevcount,
datatype );
/* all reduced on available data this step (i) complete,
* pass to the next process unless you are the root.
*/
if (rank != tree->tree_root) {
/* send combined/accumulated data to parent */
ret = MCA_PML_CALL( send( accumulator, prevcount,
datatype, tree->tree_prev,
MCA_COLL_BASE_TAG_REDUCE,
MCA_PML_BASE_SEND_STANDARD,
comm) );
if (ret != MPI_SUCCESS) {
line = __LINE__; goto error_hndl;
}
}
/* we stop when segindex = number of segments
(i.e. we do num_segment+1 steps for pipelining */
if (segindex == num_segments) break;
}
/* update input buffer index */
inbi = inbi ^ 1;
} /* end of for each child */
} /* end of for each segment */
/* clean up */
if( inbuf_free[0] != NULL) free(inbuf_free[0]);
if( inbuf_free[1] != NULL) free(inbuf_free[1]);
if( accumbuf_free != NULL ) free(accumbuf_free);
}
/* leaf nodes
Depending on the value of max_outstanding_reqs and
the number of segments we have two options:
- send all segments using blocking send to the parent, or
- avoid overflooding the parent nodes by limiting the number of
outstanding requests to max_oustanding_reqs.
TODO/POSSIBLE IMPROVEMENT: If there is a way to determine the eager size
for the current communication, synchronization should be used only
when the message/segment size is smaller than the eager size.
*/
else {
/* If the number of segments is less than a maximum number of oustanding
requests or there is no limit on the maximum number of outstanding
requests, we send data to the parent using blocking send */
if ((0 == max_outstanding_reqs) ||
(num_segments <= max_outstanding_reqs)) {
segindex = 0;
while ( original_count > 0) {
if (original_count < count_by_segment) {
count_by_segment = original_count;
}
ret = MCA_PML_CALL( send((char*)sendbuf +
(ptrdiff_t)segindex * (ptrdiff_t)segment_increment,
count_by_segment, datatype,
tree->tree_prev,
MCA_COLL_BASE_TAG_REDUCE,
MCA_PML_BASE_SEND_STANDARD,
comm) );
if (ret != MPI_SUCCESS) { line = __LINE__; goto error_hndl; }
segindex++;
original_count -= count_by_segment;
}
}
/* Otherwise, introduce flow control:
- post max_outstanding_reqs non-blocking synchronous send,
- for remaining segments
- wait for a ssend to complete, and post the next one.
- wait for all outstanding sends to complete.
*/
else {
int creq = 0;
ompi_request_t **sreq = NULL;
sreq = (ompi_request_t**) calloc( max_outstanding_reqs,
sizeof(ompi_request_t*) );
if (NULL == sreq) { line = __LINE__; ret = -1; goto error_hndl; }
/* post first group of requests */
for (segindex = 0; segindex < max_outstanding_reqs; segindex++) {
ret = MCA_PML_CALL( isend((char*)sendbuf +
(ptrdiff_t)segindex * (ptrdiff_t)segment_increment,
count_by_segment, datatype,
tree->tree_prev,
MCA_COLL_BASE_TAG_REDUCE,
MCA_PML_BASE_SEND_SYNCHRONOUS, comm,
&sreq[segindex]) );
if (ret != MPI_SUCCESS) { line = __LINE__; goto error_hndl; }
original_count -= count_by_segment;
}
creq = 0;
while ( original_count > 0 ) {
/* wait on a posted request to complete */
ret = ompi_request_wait(&sreq[creq], MPI_STATUS_IGNORE);
if (ret != MPI_SUCCESS) { line = __LINE__; goto error_hndl; }
sreq[creq] = MPI_REQUEST_NULL;
if( original_count < count_by_segment ) {
count_by_segment = original_count;
}
ret = MCA_PML_CALL( isend((char*)sendbuf +
(ptrdiff_t)segindex * (ptrdiff_t)segment_increment,
count_by_segment, datatype,
tree->tree_prev,
MCA_COLL_BASE_TAG_REDUCE,
MCA_PML_BASE_SEND_SYNCHRONOUS, comm,
&sreq[creq]) );
if (ret != MPI_SUCCESS) { line = __LINE__; goto error_hndl; }
creq = (creq + 1) % max_outstanding_reqs;
segindex++;
original_count -= count_by_segment;
}
/* Wait on the remaining request to complete */
ret = ompi_request_wait_all( max_outstanding_reqs, sreq,
MPI_STATUSES_IGNORE );
if (ret != MPI_SUCCESS) { line = __LINE__; goto error_hndl; }
/* free requests */
free(sreq);
}
}
return OMPI_SUCCESS;
error_hndl: /* error handler */
OPAL_OUTPUT (( ompi_coll_base_framework.framework_output,
"ERROR_HNDL: node %d file %s line %d error %d\n",
rank, __FILE__, line, ret ));
if( inbuf_free[0] != NULL ) free(inbuf_free[0]);
if( inbuf_free[1] != NULL ) free(inbuf_free[1]);
if( accumbuf_free != NULL ) free(accumbuf);
return ret;
}
/* Attention: this version of the reduce operations does not
work for:
- non-commutative operations
- segment sizes which are not multiplies of the extent of the datatype
meaning that at least one datatype must fit in the segment !
*/
int ompi_coll_base_reduce_intra_chain( void *sendbuf, void *recvbuf, int count,
ompi_datatype_t* datatype,
ompi_op_t* op, int root,
ompi_communicator_t* comm,
mca_coll_base_module_t *module,
uint32_t segsize, int fanout,
int max_outstanding_reqs )
{
int segcount = count;
size_t typelng;
mca_coll_base_module_t *base_module = (mca_coll_base_module_t*) module;
mca_coll_base_comm_t *data = base_module->base_data;
OPAL_OUTPUT((ompi_coll_base_framework.framework_output,"coll:base:reduce_intra_chain rank %d fo %d ss %5d", ompi_comm_rank(comm), fanout, segsize));
COLL_BASE_UPDATE_CHAIN( comm, base_module, root, fanout );
/**
* Determine number of segments and number of elements
* sent per operation
*/
ompi_datatype_type_size( datatype, &typelng );
COLL_BASE_COMPUTED_SEGCOUNT( segsize, typelng, segcount );
return ompi_coll_base_reduce_generic( sendbuf, recvbuf, count, datatype,
op, root, comm, module,
data->cached_chain,
segcount, max_outstanding_reqs );
}
int ompi_coll_base_reduce_intra_pipeline( void *sendbuf, void *recvbuf,
int count, ompi_datatype_t* datatype,
ompi_op_t* op, int root,
ompi_communicator_t* comm,
mca_coll_base_module_t *module,
uint32_t segsize,
int max_outstanding_reqs )
{
int segcount = count;
size_t typelng;
mca_coll_base_module_t *base_module = (mca_coll_base_module_t*) module;
mca_coll_base_comm_t *data = base_module->base_data;
OPAL_OUTPUT((ompi_coll_base_framework.framework_output,"coll:base:reduce_intra_pipeline rank %d ss %5d",
ompi_comm_rank(comm), segsize));
COLL_BASE_UPDATE_PIPELINE( comm, base_module, root );
/**
* Determine number of segments and number of elements
* sent per operation
*/
ompi_datatype_type_size( datatype, &typelng );
COLL_BASE_COMPUTED_SEGCOUNT( segsize, typelng, segcount );
return ompi_coll_base_reduce_generic( sendbuf, recvbuf, count, datatype,
op, root, comm, module,
data->cached_pipeline,
segcount, max_outstanding_reqs );
}
int ompi_coll_base_reduce_intra_binary( void *sendbuf, void *recvbuf,
int count, ompi_datatype_t* datatype,
ompi_op_t* op, int root,
ompi_communicator_t* comm,
mca_coll_base_module_t *module,
uint32_t segsize,
int max_outstanding_reqs )
{
int segcount = count;
size_t typelng;
mca_coll_base_module_t *base_module = (mca_coll_base_module_t*) module;
mca_coll_base_comm_t *data = base_module->base_data;
OPAL_OUTPUT((ompi_coll_base_framework.framework_output,"coll:base:reduce_intra_binary rank %d ss %5d",
ompi_comm_rank(comm), segsize));
COLL_BASE_UPDATE_BINTREE( comm, base_module, root );
/**
* Determine number of segments and number of elements
* sent per operation
*/
ompi_datatype_type_size( datatype, &typelng );
COLL_BASE_COMPUTED_SEGCOUNT( segsize, typelng, segcount );
return ompi_coll_base_reduce_generic( sendbuf, recvbuf, count, datatype,
op, root, comm, module,
data->cached_bintree,
segcount, max_outstanding_reqs );
}
int ompi_coll_base_reduce_intra_binomial( void *sendbuf, void *recvbuf,
int count, ompi_datatype_t* datatype,
ompi_op_t* op, int root,
ompi_communicator_t* comm,
mca_coll_base_module_t *module,
uint32_t segsize,
int max_outstanding_reqs )
{
int segcount = count;
size_t typelng;
mca_coll_base_module_t *base_module = (mca_coll_base_module_t*) module;
mca_coll_base_comm_t *data = base_module->base_data;
OPAL_OUTPUT((ompi_coll_base_framework.framework_output,"coll:base:reduce_intra_binomial rank %d ss %5d",
ompi_comm_rank(comm), segsize));
COLL_BASE_UPDATE_IN_ORDER_BMTREE( comm, base_module, root );
/**
* Determine number of segments and number of elements
* sent per operation
*/
ompi_datatype_type_size( datatype, &typelng );
COLL_BASE_COMPUTED_SEGCOUNT( segsize, typelng, segcount );
return ompi_coll_base_reduce_generic( sendbuf, recvbuf, count, datatype,
op, root, comm, module,
data->cached_in_order_bmtree,
segcount, max_outstanding_reqs );
}
/*
* reduce_intra_in_order_binary
*
* Function: Logarithmic reduce operation for non-commutative operations.
* Acecpts: same as MPI_Reduce()
* Returns: MPI_SUCCESS or error code
*/
int ompi_coll_base_reduce_intra_in_order_binary( void *sendbuf, void *recvbuf,
int count,
ompi_datatype_t* datatype,
ompi_op_t* op, int root,
ompi_communicator_t* comm,
mca_coll_base_module_t *module,
uint32_t segsize,
int max_outstanding_reqs )
{
int ret, rank, size, io_root, segcount = count;
void *use_this_sendbuf = NULL, *use_this_recvbuf = NULL;
size_t typelng;
mca_coll_base_module_t *base_module = (mca_coll_base_module_t*) module;
mca_coll_base_comm_t *data = base_module->base_data;
rank = ompi_comm_rank(comm);
size = ompi_comm_size(comm);
OPAL_OUTPUT((ompi_coll_base_framework.framework_output,"coll:base:reduce_intra_in_order_binary rank %d ss %5d",
rank, segsize));
COLL_BASE_UPDATE_IN_ORDER_BINTREE( comm, base_module );
/**
* Determine number of segments and number of elements
* sent per operation
*/
ompi_datatype_type_size( datatype, &typelng );
COLL_BASE_COMPUTED_SEGCOUNT( segsize, typelng, segcount );
/* An in-order binary tree must use root (size-1) to preserve the order of
operations. Thus, if root is not rank (size - 1), then we must handle
1. MPI_IN_PLACE option on real root, and
2. we must allocate temporary recvbuf on rank (size - 1).
Note that generic function must be careful not to switch order of
operations for non-commutative ops.
*/
io_root = size - 1;
use_this_sendbuf = sendbuf;
use_this_recvbuf = recvbuf;
if (io_root != root) {
ptrdiff_t tlb, text, lb, ext;
char *tmpbuf = NULL;
ompi_datatype_get_extent(datatype, &lb, &ext);
ompi_datatype_get_true_extent(datatype, &tlb, &text);
if ((root == rank) && (MPI_IN_PLACE == sendbuf)) {
tmpbuf = (char *) malloc(text + (ptrdiff_t)(count - 1) * ext);
if (NULL == tmpbuf) {
return MPI_ERR_INTERN;
}
ompi_datatype_copy_content_same_ddt(datatype, count,
(char*)tmpbuf,
(char*)recvbuf);
use_this_sendbuf = tmpbuf;
} else if (io_root == rank) {
tmpbuf = (char *) malloc(text + (ptrdiff_t)(count - 1) * ext);
if (NULL == tmpbuf) {
return MPI_ERR_INTERN;
}
use_this_recvbuf = tmpbuf;
}
}
/* Use generic reduce with in-order binary tree topology and io_root */
ret = ompi_coll_base_reduce_generic( use_this_sendbuf, use_this_recvbuf, count, datatype,
op, io_root, comm, module,
data->cached_in_order_bintree,
segcount, max_outstanding_reqs );
if (MPI_SUCCESS != ret) { return ret; }
/* Clean up */
if (io_root != root) {
if (root == rank) {
/* Receive result from rank io_root to recvbuf */
ret = MCA_PML_CALL(recv(recvbuf, count, datatype, io_root,
MCA_COLL_BASE_TAG_REDUCE, comm,
MPI_STATUS_IGNORE));
if (MPI_SUCCESS != ret) { return ret; }
if (MPI_IN_PLACE == sendbuf) {
free(use_this_sendbuf);
}
} else if (io_root == rank) {
/* Send result from use_this_recvbuf to root */
ret = MCA_PML_CALL(send(use_this_recvbuf, count, datatype, root,
MCA_COLL_BASE_TAG_REDUCE,
MCA_PML_BASE_SEND_STANDARD, comm));
if (MPI_SUCCESS != ret) { return ret; }
free(use_this_recvbuf);
}
}
return MPI_SUCCESS;
}
/*
* Linear functions are copied from the BASIC coll module
* they do not segment the message and are simple implementations
* but for some small number of nodes and/or small data sizes they
* are just as fast as base/tree based segmenting operations
* and as such may be selected by the decision functions
* These are copied into this module due to the way we select modules
* in V1. i.e. in V2 we will handle this differently and so will not
* have to duplicate code.
* GEF Oct05 after asking Jeff.
*/
/* copied function (with appropriate renaming) starts here */
/*
* reduce_lin_intra
*
* Function: - reduction using O(N) algorithm
* Accepts: - same as MPI_Reduce()
* Returns: - MPI_SUCCESS or error code
*/
int
ompi_coll_base_reduce_intra_basic_linear(void *sbuf, void *rbuf, int count,
struct ompi_datatype_t *dtype,
struct ompi_op_t *op,
int root,
struct ompi_communicator_t *comm,
mca_coll_base_module_t *module)
{
int i, rank, err, size;
ptrdiff_t true_lb, true_extent, lb, extent;
char *free_buffer = NULL;
char *pml_buffer = NULL;
char *inplace_temp = NULL;
char *inbuf;
/* Initialize */
rank = ompi_comm_rank(comm);
size = ompi_comm_size(comm);
/* If not root, send data to the root. */
if (rank != root) {
err = MCA_PML_CALL(send(sbuf, count, dtype, root,
MCA_COLL_BASE_TAG_REDUCE,
MCA_PML_BASE_SEND_STANDARD, comm));
return err;
}
/* Root receives and reduces messages. Allocate buffer to receive
* messages. This comment applies to all collectives in this basic
* module where we allocate a temporary buffer. For the next few
* lines of code, it's tremendously complicated how we decided that
* this was the Right Thing to do. Sit back and enjoy. And prepare
* to have your mind warped. :-)
*
* Recall some definitions (I always get these backwards, so I'm
* going to put them here):
*
* extent: the length from the lower bound to the upper bound -- may
* be considerably larger than the buffer required to hold the data
* (or smaller! But it's easiest to think about when it's larger).
*
* true extent: the exact number of bytes required to hold the data
* in the layout pattern in the datatype.
*
* For example, consider the following buffer (just talking about
* true_lb, extent, and true extent -- extrapolate for true_ub:
*
* A B C
* --------------------------------------------------------
* | | |
* --------------------------------------------------------
*
* There are multiple cases:
*
* 1. A is what we give to MPI_Send (and friends), and A is where
* the data starts, and C is where the data ends. In this case:
*
* - extent: C-A
* - true extent: C-A
* - true_lb: 0
*
* A C
* --------------------------------------------------------
* | |
* --------------------------------------------------------
* <=======================extent=========================>
* <======================true extent=====================>
*
* 2. A is what we give to MPI_Send (and friends), B is where the
* data starts, and C is where the data ends. In this case:
*
* - extent: C-A
* - true extent: C-B
* - true_lb: positive
*
* A B C
* --------------------------------------------------------
* | | User buffer |
* --------------------------------------------------------
* <=======================extent=========================>
* <===============true extent=============>
*
* 3. B is what we give to MPI_Send (and friends), A is where the
* data starts, and C is where the data ends. In this case:
*
* - extent: C-A
* - true extent: C-A
* - true_lb: negative
*
* A B C
* --------------------------------------------------------
* | | User buffer |
* --------------------------------------------------------
* <=======================extent=========================>
* <======================true extent=====================>
*
* 4. MPI_BOTTOM is what we give to MPI_Send (and friends), B is
* where the data starts, and C is where the data ends. In this
* case:
*
* - extent: C-MPI_BOTTOM
* - true extent: C-B
* - true_lb: [potentially very large] positive
*
* MPI_BOTTOM B C
* --------------------------------------------------------
* | | User buffer |
* --------------------------------------------------------
* <=======================extent=========================>
* <===============true extent=============>
*
* So in all cases, for a temporary buffer, all we need to malloc()
* is a buffer of size true_extent. We therefore need to know two
* pointer values: what value to give to MPI_Send (and friends) and
* what value to give to free(), because they might not be the same.
*
* Clearly, what we give to free() is exactly what was returned from
* malloc(). That part is easy. :-)
*
* What we give to MPI_Send (and friends) is a bit more complicated.
* Let's take the 4 cases from above:
*
* 1. If A is what we give to MPI_Send and A is where the data
* starts, then clearly we give to MPI_Send what we got back from
* malloc().
*
* 2. If B is what we get back from malloc, but we give A to
* MPI_Send, then the buffer range [A,B) represents "dead space"
* -- no data will be put there. So it's safe to give B-true_lb to
* MPI_Send. More specifically, the true_lb is positive, so B-true_lb is
* actually A.
*
* 3. If A is what we get back from malloc, and B is what we give to
* MPI_Send, then the true_lb is negative, so A-true_lb will actually equal
* B.
*
* 4. Although this seems like the weirdest case, it's actually
* quite similar to case #2 -- the pointer we give to MPI_Send is
* smaller than the pointer we got back from malloc().
*
* Hence, in all cases, we give (return_from_malloc - true_lb) to MPI_Send.
*
* This works fine and dandy if we only have (count==1), which we
* rarely do. ;-) So we really need to allocate (true_extent +
* ((count - 1) * extent)) to get enough space for the rest. This may
* be more than is necessary, but it's ok.
*
* Simple, no? :-)
*
*/
ompi_datatype_get_extent(dtype, &lb, &extent);
ompi_datatype_get_true_extent(dtype, &true_lb, &true_extent);
if (MPI_IN_PLACE == sbuf) {
sbuf = rbuf;
inplace_temp = (char*)malloc(true_extent + (count - 1) * extent);
if (NULL == inplace_temp) {
return OMPI_ERR_OUT_OF_RESOURCE;
}
rbuf = inplace_temp - true_lb;
}
if (size > 1) {
free_buffer = (char*)malloc(true_extent + (count - 1) * extent);
if (NULL == free_buffer) {
if (NULL != inplace_temp) {
free(inplace_temp);
}
return OMPI_ERR_OUT_OF_RESOURCE;
}
pml_buffer = free_buffer - true_lb;
}
/* Initialize the receive buffer. */
if (rank == (size - 1)) {
err = ompi_datatype_copy_content_same_ddt(dtype, count, (char*)rbuf, (char*)sbuf);
} else {
err = MCA_PML_CALL(recv(rbuf, count, dtype, size - 1,
MCA_COLL_BASE_TAG_REDUCE, comm,
MPI_STATUS_IGNORE));
}
if (MPI_SUCCESS != err) {
if (NULL != free_buffer) {
free(free_buffer);
}
return err;
}
/* Loop receiving and calling reduction function (C or Fortran). */
for (i = size - 2; i >= 0; --i) {
if (rank == i) {
inbuf = (char*)sbuf;
} else {
err = MCA_PML_CALL(recv(pml_buffer, count, dtype, i,
MCA_COLL_BASE_TAG_REDUCE, comm,
MPI_STATUS_IGNORE));
if (MPI_SUCCESS != err) {
if (NULL != free_buffer) {
free(free_buffer);
}
return err;
}
inbuf = pml_buffer;
}
/* Perform the reduction */
ompi_op_reduce(op, inbuf, rbuf, count, dtype);
}
if (NULL != inplace_temp) {
err = ompi_datatype_copy_content_same_ddt(dtype, count, (char*)sbuf, inplace_temp);
free(inplace_temp);
}
if (NULL != free_buffer) {
free(free_buffer);
}
/* All done */
return MPI_SUCCESS;
}
/* copied function (with appropriate renaming) ends here */