/* -*- 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 */