openmpi/ompi/mca/coll/tuned/coll_tuned_allreduce.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) 2004-2012 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) 2009      University of Houston. All rights reserved.
 * Copyright (c) 2013      Los Alamos National Security, LLC. 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/base/coll_tags.h"
#include "ompi/mca/pml/pml.h"
#include "ompi/op/op.h"
#include "coll_tuned.h"
#include "coll_tuned_topo.h"
#include "coll_tuned_util.h"

/* allreduce algorithm variables */
static int coll_tuned_allreduce_algorithm_count = 5;
static int coll_tuned_allreduce_forced_algorithm = 0;
static int coll_tuned_allreduce_segment_size = 0;
static int coll_tuned_allreduce_tree_fanout;
static int coll_tuned_allreduce_chain_fanout;

/* valid values for coll_tuned_allreduce_forced_algorithm */
static mca_base_var_enum_value_t allreduce_algorithms[] = {
    {0, "ignore"},
    {1, "basic_linear"},
    {2, "nonoverlapping"},
    {3, "recursive_doubling"},
    {4, "ring"},
    {5, "segmented_ring"},
    {0, NULL}
};

/*
 * ompi_coll_tuned_allreduce_intra_nonoverlapping
 *
 * This function just calls a reduce followed by a broadcast
 * both called functions are tuned but they complete sequentially,
 * i.e. no additional overlapping
 * meaning if the number of segments used is greater than the topo depth 
 * then once the first segment of data is fully 'reduced' it is not broadcast
 * while the reduce continues (cost = cost-reduce + cost-bcast + decision x 3)
 *
 */
int
ompi_coll_tuned_allreduce_intra_nonoverlapping(void *sbuf, void *rbuf, int count,
                                               struct ompi_datatype_t *dtype,
                                               struct ompi_op_t *op,
                                               struct ompi_communicator_t *comm,
                                               mca_coll_base_module_t *module)
{
    int err, rank;

    rank = ompi_comm_rank(comm);

    OPAL_OUTPUT((ompi_coll_tuned_stream,"coll:tuned:allreduce_intra_nonoverlapping rank %d", rank));

    /* Reduce to 0 and broadcast. */

    if (MPI_IN_PLACE == sbuf) {
        if (0 == rank) {
            err = comm->c_coll.coll_reduce (MPI_IN_PLACE, rbuf, count, dtype, 
                                            op, 0, comm, comm->c_coll.coll_reduce_module);
        } else {
            err = comm->c_coll.coll_reduce (rbuf, NULL, count, dtype, op, 0, 
                                            comm, comm->c_coll.coll_reduce_module);
        }
    } else {
        err = comm->c_coll.coll_reduce (sbuf, rbuf, count, dtype, op, 0,
                                        comm, comm->c_coll.coll_reduce_module);
    }
    if (MPI_SUCCESS != err) {
        return err;
    }

    return comm->c_coll.coll_bcast (rbuf, count, dtype, 0, comm,
                                    comm->c_coll.coll_bcast_module);
}

/*
 *   ompi_coll_tuned_allreduce_intra_recursivedoubling
 *
 *   Function:       Recursive doubling algorithm for allreduce operation
 *   Accepts:        Same as MPI_Allreduce()
 *   Returns:        MPI_SUCCESS or error code
 *
 *   Description:    Implements recursive doubling algorithm for allreduce.  
 *                   Original (non-segmented) implementation is used in MPICH-2 
 *                   for small and intermediate size messages.
 *                   The algorithm preserves order of operations so it can 
 *                   be used both by commutative and non-commutative operations.
 *
 *         Example on 7 nodes:
 *         Initial state
 *         #      0       1      2       3      4       5      6 
 *               [0]     [1]    [2]     [3]    [4]     [5]    [6]
 *         Initial adjustment step for non-power of two nodes.
 *         old rank      1              3              5      6
 *         new rank      0              1              2      3
 *                     [0+1]          [2+3]          [4+5]   [6]
 *         Step 1
 *         old rank      1              3              5      6
 *         new rank      0              1              2      3
 *                     [0+1+]         [0+1+]         [4+5+]  [4+5+]
 *                     [2+3+]         [2+3+]         [6   ]  [6   ]
 *         Step 2
 *         old rank      1              3              5      6
 *         new rank      0              1              2      3
 *                     [0+1+]         [0+1+]         [0+1+]  [0+1+]
 *                     [2+3+]         [2+3+]         [2+3+]  [2+3+]  
 *                     [4+5+]         [4+5+]         [4+5+]  [4+5+]
 *                     [6   ]         [6   ]         [6   ]  [6   ]
 *         Final adjustment step for non-power of two nodes
 *         #      0       1      2       3      4       5      6 
 *              [0+1+] [0+1+] [0+1+]  [0+1+] [0+1+]  [0+1+] [0+1+]
 *              [2+3+] [2+3+] [2+3+]  [2+3+] [2+3+]  [2+3+] [2+3+] 
 *              [4+5+] [4+5+] [4+5+]  [4+5+] [4+5+]  [4+5+] [4+5+]
 *              [6   ] [6   ] [6   ]  [6   ] [6   ]  [6   ] [6   ]
 *
 */
int 
ompi_coll_tuned_allreduce_intra_recursivedoubling(void *sbuf, void *rbuf, 
                                                  int count,
                                                  struct ompi_datatype_t *dtype,
                                                  struct ompi_op_t *op,
                                                  struct ompi_communicator_t *comm,
                                                  mca_coll_base_module_t *module) 
{
    int ret, line, rank, size, adjsize, remote, distance;
    int newrank, newremote, extra_ranks;
    char *tmpsend = NULL, *tmprecv = NULL, *tmpswap = NULL, *inplacebuf = NULL;
    ptrdiff_t true_lb, true_extent, lb, extent;
    ompi_request_t *reqs[2] = {NULL, NULL};

    size = ompi_comm_size(comm);
    rank = ompi_comm_rank(comm);

    OPAL_OUTPUT((ompi_coll_tuned_stream,
                 "coll:tuned:allreduce_intra_recursivedoubling rank %d", rank));
   
    /* Special case for size == 1 */
    if (1 == size) {
        if (MPI_IN_PLACE != sbuf) {
            ret = ompi_datatype_copy_content_same_ddt(dtype, count, (char*)rbuf, (char*)sbuf);
            if (ret < 0) { line = __LINE__; goto error_hndl; }
        }
        return MPI_SUCCESS;
    }

    /* Allocate and initialize temporary send buffer */
    ret = ompi_datatype_get_extent(dtype, &lb, &extent);
    if (MPI_SUCCESS != ret) { line = __LINE__; goto error_hndl; }
    ret = ompi_datatype_get_true_extent(dtype, &true_lb, &true_extent);
    if (MPI_SUCCESS != ret) { line = __LINE__; goto error_hndl; }

    inplacebuf = (char*) malloc(true_extent + (ptrdiff_t)(count - 1) * extent);
    if (NULL == inplacebuf) { ret = -1; line = __LINE__; goto error_hndl; }

    if (MPI_IN_PLACE == sbuf) {
        ret = ompi_datatype_copy_content_same_ddt(dtype, count, inplacebuf, (char*)rbuf);
        if (ret < 0) { line = __LINE__; goto error_hndl; }
    } else {
        ret = ompi_datatype_copy_content_same_ddt(dtype, count, inplacebuf, (char*)sbuf);
        if (ret < 0) { line = __LINE__; goto error_hndl; }
    }

    tmpsend = (char*) inplacebuf;
    tmprecv = (char*) rbuf;

    /* Determine nearest power of two less than or equal to size */
    adjsize = opal_next_poweroftwo (size);
    adjsize >>= 1;

    /* Handle non-power-of-two case:
       - Even ranks less than 2 * extra_ranks send their data to (rank + 1), and 
       sets new rank to -1.
       - Odd ranks less than 2 * extra_ranks receive data from (rank - 1), 
       apply appropriate operation, and set new rank to rank/2
       - Everyone else sets rank to rank - extra_ranks
    */
    extra_ranks = size - adjsize;
    if (rank <  (2 * extra_ranks)) {
        if (0 == (rank % 2)) {
            ret = MCA_PML_CALL(send(tmpsend, count, dtype, (rank + 1), 
                                    MCA_COLL_BASE_TAG_ALLREDUCE,
                                    MCA_PML_BASE_SEND_STANDARD, comm));
            if (MPI_SUCCESS != ret) { line = __LINE__; goto error_hndl; }
            newrank = -1;
        } else {
            ret = MCA_PML_CALL(recv(tmprecv, count, dtype, (rank - 1),
                                    MCA_COLL_BASE_TAG_ALLREDUCE, comm,
                                    MPI_STATUS_IGNORE));
            if (MPI_SUCCESS != ret) { line = __LINE__; goto error_hndl; }
            /* tmpsend = tmprecv (op) tmpsend */
            ompi_op_reduce(op, tmprecv, tmpsend, count, dtype);
            newrank = rank >> 1;
        }
    } else {
        newrank = rank - extra_ranks;
    }

    /* Communication/Computation loop 
       - Exchange message with remote node.
       - Perform appropriate operation taking in account order of operations:
       result = value (op) result
    */
    for (distance = 0x1; distance < adjsize; distance <<=1) {
        if (newrank < 0) break;
        /* Determine remote node */
        newremote = newrank ^ distance;
        remote = (newremote < extra_ranks)? 
            (newremote * 2 + 1):(newremote + extra_ranks);

        /* Exchange the data */
        ret = MCA_PML_CALL(irecv(tmprecv, count, dtype, remote,
                                 MCA_COLL_BASE_TAG_ALLREDUCE, comm, &reqs[0]));
        if (MPI_SUCCESS != ret) { line = __LINE__; goto error_hndl; }
        ret = MCA_PML_CALL(isend(tmpsend, count, dtype, remote, 
                                 MCA_COLL_BASE_TAG_ALLREDUCE,
                                 MCA_PML_BASE_SEND_STANDARD, comm, &reqs[1]));
        if (MPI_SUCCESS != ret) { line = __LINE__; goto error_hndl; }
        ret = ompi_request_wait_all(2, reqs, MPI_STATUSES_IGNORE);
        if (MPI_SUCCESS != ret) { line = __LINE__; goto error_hndl; }

        /* Apply operation */
        if (rank < remote) {
            /* tmprecv = tmpsend (op) tmprecv */
            ompi_op_reduce(op, tmpsend, tmprecv, count, dtype);
            tmpswap = tmprecv;
            tmprecv = tmpsend;
            tmpsend = tmpswap;
        } else {
            /* tmpsend = tmprecv (op) tmpsend */
            ompi_op_reduce(op, tmprecv, tmpsend, count, dtype);
        }
    }

    /* Handle non-power-of-two case:
       - Odd ranks less than 2 * extra_ranks send result from tmpsend to 
       (rank - 1)
       - Even ranks less than 2 * extra_ranks receive result from (rank + 1)
    */
    if (rank < (2 * extra_ranks)) {
        if (0 == (rank % 2)) {
            ret = MCA_PML_CALL(recv(rbuf, count, dtype, (rank + 1),
                                    MCA_COLL_BASE_TAG_ALLREDUCE, comm, 
                                    MPI_STATUS_IGNORE));
            if (MPI_SUCCESS != ret) { line = __LINE__; goto error_hndl; }
            tmpsend = (char*)rbuf;
        } else {
            ret = MCA_PML_CALL(send(tmpsend, count, dtype, (rank - 1),
                                    MCA_COLL_BASE_TAG_ALLREDUCE,
                                    MCA_PML_BASE_SEND_STANDARD, comm));
            if (MPI_SUCCESS != ret) { line = __LINE__; goto error_hndl; }
        }
    }

    /* Ensure that the final result is in rbuf */
    if (tmpsend != rbuf) {
        ret = ompi_datatype_copy_content_same_ddt(dtype, count, (char*)rbuf, tmpsend);
        if (ret < 0) { line = __LINE__; goto error_hndl; }
    }

    if (NULL != inplacebuf) free(inplacebuf);
    return MPI_SUCCESS;

 error_hndl:
    OPAL_OUTPUT((ompi_coll_tuned_stream, "%s:%4d\tRank %d Error occurred %d\n",
                 __FILE__, line, rank, ret));
    if (NULL != inplacebuf) free(inplacebuf);
    return ret;
}

/*
 *   ompi_coll_tuned_allreduce_intra_ring
 *
 *   Function:       Ring algorithm for allreduce operation
 *   Accepts:        Same as MPI_Allreduce()
 *   Returns:        MPI_SUCCESS or error code
 *
 *   Description:    Implements ring algorithm for allreduce: the message is
 *                   automatically segmented to segment of size M/N.
 *                   Algorithm requires 2*N - 1 steps.
 *
 *   Limitations:    The algorithm DOES NOT preserve order of operations so it 
 *                   can be used only for commutative operations.
 *                   In addition, algorithm cannot work if the total count is 
 *                   less than size.
 *         Example on 5 nodes:
 *         Initial state
 *   #      0              1             2              3             4
 *        [00]           [10]          [20]           [30]           [40]
 *        [01]           [11]          [21]           [31]           [41]
 *        [02]           [12]          [22]           [32]           [42]
 *        [03]           [13]          [23]           [33]           [43]
 *        [04]           [14]          [24]           [34]           [44]
 *
 *        COMPUTATION PHASE
 *         Step 0: rank r sends block r to rank (r+1) and receives bloc (r-1) 
 *                 from rank (r-1) [with wraparound].
 *    #     0              1             2              3             4
 *        [00]          [00+10]        [20]           [30]           [40]
 *        [01]           [11]         [11+21]         [31]           [41]
 *        [02]           [12]          [22]          [22+32]         [42]
 *        [03]           [13]          [23]           [33]         [33+43]
 *      [44+04]          [14]          [24]           [34]           [44]
 *
 *         Step 1: rank r sends block (r-1) to rank (r+1) and receives bloc 
 *                 (r-2) from rank (r-1) [with wraparound].
 *    #      0              1             2              3             4
 *         [00]          [00+10]     [01+10+20]        [30]           [40]
 *         [01]           [11]         [11+21]      [11+21+31]        [41]
 *         [02]           [12]          [22]          [22+32]      [22+32+42]
 *      [33+43+03]        [13]          [23]           [33]         [33+43]
 *        [44+04]       [44+04+14]       [24]           [34]           [44]
 *
 *         Step 2: rank r sends block (r-2) to rank (r+1) and receives bloc 
 *                 (r-2) from rank (r-1) [with wraparound].
 *    #      0              1             2              3             4
 *         [00]          [00+10]     [01+10+20]    [01+10+20+30]      [40]
 *         [01]           [11]         [11+21]      [11+21+31]    [11+21+31+41]
 *     [22+32+42+02]      [12]          [22]          [22+32]      [22+32+42]
 *      [33+43+03]    [33+43+03+13]     [23]           [33]         [33+43]
 *        [44+04]       [44+04+14]  [44+04+14+24]      [34]           [44]
 *
 *         Step 3: rank r sends block (r-3) to rank (r+1) and receives bloc 
 *                 (r-3) from rank (r-1) [with wraparound].
 *    #      0              1             2              3             4
 *         [00]          [00+10]     [01+10+20]    [01+10+20+30]     [FULL]
 *        [FULL]           [11]        [11+21]      [11+21+31]    [11+21+31+41]
 *     [22+32+42+02]     [FULL]          [22]         [22+32]      [22+32+42]
 *      [33+43+03]    [33+43+03+13]     [FULL]          [33]         [33+43]
 *        [44+04]       [44+04+14]  [44+04+14+24]      [FULL]         [44]
 *         
 *        DISTRIBUTION PHASE: ring ALLGATHER with ranks shifted by 1.
 *
 */
int 
ompi_coll_tuned_allreduce_intra_ring(void *sbuf, void *rbuf, int count,
                                     struct ompi_datatype_t *dtype,
                                     struct ompi_op_t *op,
                                     struct ompi_communicator_t *comm,
                                     mca_coll_base_module_t *module) 
{
    int ret, line, rank, size, k, recv_from, send_to, block_count, inbi;
    int early_segcount, late_segcount, split_rank, max_segcount;
    size_t typelng;
    char *tmpsend = NULL, *tmprecv = NULL, *inbuf[2] = {NULL, NULL};
    ptrdiff_t true_lb, true_extent, lb, extent;
    ptrdiff_t block_offset, max_real_segsize;
    ompi_request_t *reqs[2] = {NULL, NULL};

    size = ompi_comm_size(comm);
    rank = ompi_comm_rank(comm);

    OPAL_OUTPUT((ompi_coll_tuned_stream,
                 "coll:tuned:allreduce_intra_ring rank %d, count %d", rank, count));
      
    /* Special case for size == 1 */
    if (1 == size) {
        if (MPI_IN_PLACE != sbuf) {
            ret = ompi_datatype_copy_content_same_ddt(dtype, count, (char*)rbuf, (char*)sbuf);
            if (ret < 0) { line = __LINE__; goto error_hndl; }
        }
        return MPI_SUCCESS;
    }

    /* Special case for count less than size - use recursive doubling */
    if (count < size) {
        OPAL_OUTPUT((ompi_coll_tuned_stream, "coll:tuned:allreduce_ring rank %d/%d, count %d, switching to recursive doubling", rank, size, count));
        return (ompi_coll_tuned_allreduce_intra_recursivedoubling(sbuf, rbuf, 
                                                                  count,
                                                                  dtype, op, 
                                                                  comm, module));
    }

    /* Allocate and initialize temporary buffers */
    ret = ompi_datatype_get_extent(dtype, &lb, &extent);
    if (MPI_SUCCESS != ret) { line = __LINE__; goto error_hndl; }
    ret = ompi_datatype_get_true_extent(dtype, &true_lb, &true_extent);
    if (MPI_SUCCESS != ret) { line = __LINE__; goto error_hndl; }
    ret = ompi_datatype_type_size( dtype, &typelng);
    if (MPI_SUCCESS != ret) { line = __LINE__; goto error_hndl; }

    /* Determine the number of elements per block and corresponding 
       block sizes.
       The blocks are divided into "early" and "late" ones:
       blocks 0 .. (split_rank - 1) are "early" and 
       blocks (split_rank) .. (size - 1) are "late".
       Early blocks are at most 1 element larger than the late ones.
    */
    COLL_TUNED_COMPUTE_BLOCKCOUNT( count, size, split_rank, 
                                   early_segcount, late_segcount )
        max_segcount = early_segcount;
    max_real_segsize = true_extent + (max_segcount - 1) * extent;


    inbuf[0] = (char*)malloc(max_real_segsize);
    if (NULL == inbuf[0]) { ret = -1; line = __LINE__; goto error_hndl; }
    if (size > 2) {
        inbuf[1] = (char*)malloc(max_real_segsize);
        if (NULL == inbuf[1]) { ret = -1; line = __LINE__; goto error_hndl; }
    }

    /* Handle MPI_IN_PLACE */
    if (MPI_IN_PLACE != sbuf) {
        ret = ompi_datatype_copy_content_same_ddt(dtype, count, (char*)rbuf, (char*)sbuf);
        if (ret < 0) { line = __LINE__; goto error_hndl; }
    }

    /* Computation loop */

    /* 
       For each of the remote nodes:
       - post irecv for block (r-1)
       - send block (r)
       - in loop for every step k = 2 .. n
       - post irecv for block (r + n - k) % n
       - wait on block (r + n - k + 1) % n to arrive
       - compute on block (r + n - k + 1) % n
       - send block (r + n - k + 1) % n
       - wait on block (r + 1)
       - compute on block (r + 1)
       - send block (r + 1) to rank (r + 1)
       Note that we must be careful when computing the begining of buffers and
       for send operations and computation we must compute the exact block size.
    */
    send_to = (rank + 1) % size;
    recv_from = (rank + size - 1) % size;

    inbi = 0;
    /* Initialize first receive from the neighbor on the left */
    ret = MCA_PML_CALL(irecv(inbuf[inbi], max_segcount, dtype, recv_from,
                             MCA_COLL_BASE_TAG_ALLREDUCE, comm, &reqs[inbi]));
    if (MPI_SUCCESS != ret) { line = __LINE__; goto error_hndl; }
    /* Send first block (my block) to the neighbor on the right */
    block_offset = ((rank < split_rank)? 
                    ((ptrdiff_t)rank * (ptrdiff_t)early_segcount) : 
                    ((ptrdiff_t)rank * (ptrdiff_t)late_segcount + split_rank));
    block_count = ((rank < split_rank)? early_segcount : late_segcount);
    tmpsend = ((char*)rbuf) + block_offset * extent;
    ret = MCA_PML_CALL(send(tmpsend, block_count, dtype, send_to,
                            MCA_COLL_BASE_TAG_ALLREDUCE,
                            MCA_PML_BASE_SEND_STANDARD, comm));
    if (MPI_SUCCESS != ret) { line = __LINE__; goto error_hndl; }
   
    for (k = 2; k < size; k++) {
        const int prevblock = (rank + size - k + 1) % size;
      
        inbi = inbi ^ 0x1;
      
        /* Post irecv for the current block */
        ret = MCA_PML_CALL(irecv(inbuf[inbi], max_segcount, dtype, recv_from,
                                 MCA_COLL_BASE_TAG_ALLREDUCE, comm, &reqs[inbi]));
        if (MPI_SUCCESS != ret) { line = __LINE__; goto error_hndl; }
      
        /* Wait on previous block to arrive */
        ret = ompi_request_wait(&reqs[inbi ^ 0x1], MPI_STATUS_IGNORE);
        if (MPI_SUCCESS != ret) { line = __LINE__; goto error_hndl; }
      
        /* Apply operation on previous block: result goes to rbuf
           rbuf[prevblock] = inbuf[inbi ^ 0x1] (op) rbuf[prevblock]
        */
        block_offset = ((prevblock < split_rank)?
                        ((ptrdiff_t)prevblock * early_segcount) :
                        ((ptrdiff_t)prevblock * late_segcount + split_rank));
        block_count = ((prevblock < split_rank)? early_segcount : late_segcount);
        tmprecv = ((char*)rbuf) + (ptrdiff_t)block_offset * extent;
        ompi_op_reduce(op, inbuf[inbi ^ 0x1], tmprecv, block_count, dtype);
      
        /* send previous block to send_to */
        ret = MCA_PML_CALL(send(tmprecv, block_count, dtype, send_to,
                                MCA_COLL_BASE_TAG_ALLREDUCE,
                                MCA_PML_BASE_SEND_STANDARD, comm));
        if (MPI_SUCCESS != ret) { line = __LINE__; goto error_hndl; }
    }

    /* Wait on the last block to arrive */
    ret = ompi_request_wait(&reqs[inbi], MPI_STATUS_IGNORE);
    if (MPI_SUCCESS != ret) { line = __LINE__; goto error_hndl; }

    /* Apply operation on the last block (from neighbor (rank + 1) 
       rbuf[rank+1] = inbuf[inbi] (op) rbuf[rank + 1] */
    recv_from = (rank + 1) % size;
    block_offset = ((recv_from < split_rank)?
                    ((ptrdiff_t)recv_from * early_segcount) :
                    ((ptrdiff_t)recv_from * late_segcount + split_rank));
    block_count = ((recv_from < split_rank)? early_segcount : late_segcount);
    tmprecv = ((char*)rbuf) + (ptrdiff_t)block_offset * extent;
    ompi_op_reduce(op, inbuf[inbi], tmprecv, block_count, dtype);
   
    /* Distribution loop - variation of ring allgather */
    send_to = (rank + 1) % size;
    recv_from = (rank + size - 1) % size;
    for (k = 0; k < size - 1; k++) {
        const int recv_data_from = (rank + size - k) % size;
        const int send_data_from = (rank + 1 + size - k) % size;
        const int send_block_offset = 
            ((send_data_from < split_rank)?
             ((ptrdiff_t)send_data_from * early_segcount) :
             ((ptrdiff_t)send_data_from * late_segcount + split_rank));
        const int recv_block_offset = 
            ((recv_data_from < split_rank)?
             ((ptrdiff_t)recv_data_from * early_segcount) :
             ((ptrdiff_t)recv_data_from * late_segcount + split_rank));
        block_count = ((send_data_from < split_rank)? 
                       early_segcount : late_segcount);

        tmprecv = (char*)rbuf + (ptrdiff_t)recv_block_offset * extent;
        tmpsend = (char*)rbuf + (ptrdiff_t)send_block_offset * extent;

        ret = ompi_coll_tuned_sendrecv(tmpsend, block_count, dtype, send_to,
                                       MCA_COLL_BASE_TAG_ALLREDUCE,
                                       tmprecv, max_segcount, dtype, recv_from,
                                       MCA_COLL_BASE_TAG_ALLREDUCE,
                                       comm, MPI_STATUS_IGNORE, rank);
        if (MPI_SUCCESS != ret) { line = __LINE__; goto error_hndl;}

    }

    if (NULL != inbuf[0]) free(inbuf[0]);
    if (NULL != inbuf[1]) free(inbuf[1]);

    return MPI_SUCCESS;

 error_hndl:
    OPAL_OUTPUT((ompi_coll_tuned_stream, "%s:%4d\tRank %d Error occurred %d\n",
                 __FILE__, line, rank, ret));
    if (NULL != inbuf[0]) free(inbuf[0]);
    if (NULL != inbuf[1]) free(inbuf[1]);
    return ret;
}

/*
 *   ompi_coll_tuned_allreduce_intra_ring_segmented
 *
 *   Function:       Pipelined ring algorithm for allreduce operation
 *   Accepts:        Same as MPI_Allreduce(), segment size
 *   Returns:        MPI_SUCCESS or error code
 *
 *   Description:    Implements pipelined ring algorithm for allreduce: 
 *                   user supplies suggested segment size for the pipelining of
 *                   reduce operation.
 *                   The segment size determines the number of phases, np, for 
 *                   the algorithm execution.  
 *                   The message is automatically divided into blocks of 
 *                   approximately  (count / (np * segcount)) elements.
 *                   At the end of reduction phase, allgather like step is 
 *                   executed.
 *                   Algorithm requires (np + 1)*(N - 1) steps.
 *
 *   Limitations:    The algorithm DOES NOT preserve order of operations so it 
 *                   can be used only for commutative operations.
 *                   In addition, algorithm cannot work if the total size is 
 *                   less than size * segment size.
 *         Example on 3 nodes with 2 phases
 *         Initial state
 *   #      0              1             2 
 *        [00a]          [10a]         [20a]
 *        [00b]          [10b]         [20b]
 *        [01a]          [11a]         [21a]
 *        [01b]          [11b]         [21b]
 *        [02a]          [12a]         [22a]
 *        [02b]          [12b]         [22b]
 *
 *        COMPUTATION PHASE 0 (a)
 *         Step 0: rank r sends block ra to rank (r+1) and receives bloc (r-1)a 
 *                 from rank (r-1) [with wraparound].
 *    #     0              1             2  
 *        [00a]        [00a+10a]       [20a]
 *        [00b]          [10b]         [20b]
 *        [01a]          [11a]       [11a+21a]
 *        [01b]          [11b]         [21b]
 *      [22a+02a]        [12a]         [22a]
 *        [02b]          [12b]         [22b]
 *
 *         Step 1: rank r sends block (r-1)a to rank (r+1) and receives bloc 
 *                 (r-2)a from rank (r-1) [with wraparound].
 *    #     0              1             2  
 *        [00a]        [00a+10a]   [00a+10a+20a]
 *        [00b]          [10b]         [20b]
 *    [11a+21a+01a]      [11a]       [11a+21a]
 *        [01b]          [11b]         [21b]
 *      [22a+02a]    [22a+02a+12a]     [22a]
 *        [02b]          [12b]         [22b] 
 *
 *        COMPUTATION PHASE 1 (b)
 *         Step 0: rank r sends block rb to rank (r+1) and receives bloc (r-1)b 
 *                 from rank (r-1) [with wraparound].
 *    #     0              1             2  
 *        [00a]        [00a+10a]       [20a]
 *        [00b]        [00b+10b]       [20b]
 *        [01a]          [11a]       [11a+21a]
 *        [01b]          [11b]       [11b+21b]
 *      [22a+02a]        [12a]         [22a]
 *      [22b+02b]        [12b]         [22b]
 *
 *         Step 1: rank r sends block (r-1)b to rank (r+1) and receives bloc 
 *                 (r-2)b from rank (r-1) [with wraparound].
 *    #     0              1             2  
 *        [00a]        [00a+10a]   [00a+10a+20a]
 *        [00b]          [10b]     [0bb+10b+20b]
 *    [11a+21a+01a]      [11a]       [11a+21a]
 *    [11b+21b+01b]      [11b]         [21b]
 *      [22a+02a]    [22a+02a+12a]     [22a]
 *        [02b]      [22b+01b+12b]     [22b] 
 *
 *         
 *        DISTRIBUTION PHASE: ring ALLGATHER with ranks shifted by 1 (same as
 *         in regular ring algorithm.
 *
 */
int 
ompi_coll_tuned_allreduce_intra_ring_segmented(void *sbuf, void *rbuf, int count,
                                               struct ompi_datatype_t *dtype,
                                               struct ompi_op_t *op,
                                               struct ompi_communicator_t *comm,
                                               mca_coll_base_module_t *module,
                                               uint32_t segsize) 
{
    int ret, line, rank, size, k, recv_from, send_to;
    int early_blockcount, late_blockcount, split_rank; 
    int segcount, max_segcount, num_phases, phase, block_count, inbi;
    size_t typelng;
    char *tmpsend = NULL, *tmprecv = NULL, *inbuf[2] = {NULL, NULL};
    ptrdiff_t true_lb, true_extent, lb, extent;
    ptrdiff_t block_offset, max_real_segsize;
    ompi_request_t *reqs[2] = {NULL, NULL};

    size = ompi_comm_size(comm);
    rank = ompi_comm_rank(comm);

    OPAL_OUTPUT((ompi_coll_tuned_stream,
                 "coll:tuned:allreduce_intra_ring_segmented rank %d, count %d", rank, count));
      
    /* Special case for size == 1 */
    if (1 == size) {
        if (MPI_IN_PLACE != sbuf) {
            ret = ompi_datatype_copy_content_same_ddt(dtype, count, (char*)rbuf, (char*)sbuf);
            if (ret < 0) { line = __LINE__; goto error_hndl; }
        }
        return MPI_SUCCESS;
    }

    /* Determine segment count based on the suggested segment size */
    ret = ompi_datatype_get_extent(dtype, &lb, &extent);
    if (MPI_SUCCESS != ret) { line = __LINE__; goto error_hndl; }
    ret = ompi_datatype_get_true_extent(dtype, &true_lb, &true_extent);
    if (MPI_SUCCESS != ret) { line = __LINE__; goto error_hndl; }
    ret = ompi_datatype_type_size( dtype, &typelng);
    if (MPI_SUCCESS != ret) { line = __LINE__; goto error_hndl; }
    segcount = count;
    COLL_TUNED_COMPUTED_SEGCOUNT(segsize, typelng, segcount)

        /* Special case for count less than size * segcount - use regular ring */
        if (count < (size * segcount)) {
            OPAL_OUTPUT((ompi_coll_tuned_stream, "coll:tuned:allreduce_ring_segmented rank %d/%d, count %d, switching to regular ring", rank, size, count));
            return (ompi_coll_tuned_allreduce_intra_ring(sbuf, rbuf, count, dtype, op, 
                                                         comm, module));
        }

    /* Determine the number of phases of the algorithm */
    num_phases = count / (size * segcount);
    if ((count % (size * segcount) >= size) && 
        (count % (size * segcount) > ((size * segcount) / 2))) {
        num_phases++;
    }

    /* Determine the number of elements per block and corresponding 
       block sizes.
       The blocks are divided into "early" and "late" ones:
       blocks 0 .. (split_rank - 1) are "early" and 
       blocks (split_rank) .. (size - 1) are "late".
       Early blocks are at most 1 element larger than the late ones.
       Note, these blocks will be split into num_phases segments,
       out of the largest one will have max_segcount elements.
    */
    COLL_TUNED_COMPUTE_BLOCKCOUNT( count, size, split_rank, 
                                   early_blockcount, late_blockcount )
        COLL_TUNED_COMPUTE_BLOCKCOUNT( early_blockcount, num_phases, inbi,
                                       max_segcount, k)
        max_real_segsize = true_extent + (ptrdiff_t)(max_segcount - 1) * extent;

    /* Allocate and initialize temporary buffers */
    inbuf[0] = (char*)malloc(max_real_segsize);
    if (NULL == inbuf[0]) { ret = -1; line = __LINE__; goto error_hndl; }
    if (size > 2) {
        inbuf[1] = (char*)malloc(max_real_segsize);
        if (NULL == inbuf[1]) { ret = -1; line = __LINE__; goto error_hndl; }
    }

    /* Handle MPI_IN_PLACE */
    if (MPI_IN_PLACE != sbuf) {
        ret = ompi_datatype_copy_content_same_ddt(dtype, count, (char*)rbuf, (char*)sbuf);
        if (ret < 0) { line = __LINE__; goto error_hndl; }
    }

    /* Computation loop: for each phase, repeat ring allreduce computation loop */
    for (phase = 0; phase < num_phases; phase ++) {
        ptrdiff_t phase_offset;
        int early_phase_segcount, late_phase_segcount, split_phase, phase_count;

        /* 
           For each of the remote nodes:
           - post irecv for block (r-1)
           - send block (r)
           To do this, first compute block offset and count, and use block offset
           to compute phase offset.
           - in loop for every step k = 2 .. n
           - post irecv for block (r + n - k) % n
           - wait on block (r + n - k + 1) % n to arrive
           - compute on block (r + n - k + 1) % n
           - send block (r + n - k + 1) % n
           - wait on block (r + 1)
           - compute on block (r + 1)
           - send block (r + 1) to rank (r + 1)
           Note that we must be careful when computing the begining of buffers and
           for send operations and computation we must compute the exact block size.
        */
        send_to = (rank + 1) % size;
        recv_from = (rank + size - 1) % size;
      
        inbi = 0;
        /* Initialize first receive from the neighbor on the left */
        ret = MCA_PML_CALL(irecv(inbuf[inbi], max_segcount, dtype, recv_from,
                                 MCA_COLL_BASE_TAG_ALLREDUCE, comm, &reqs[inbi]));
        if (MPI_SUCCESS != ret) { line = __LINE__; goto error_hndl; }
        /* Send first block (my block) to the neighbor on the right:
           - compute my block and phase offset
           - send data */
        block_offset = ((rank < split_rank)? 
                        ((ptrdiff_t)rank * (ptrdiff_t)early_blockcount) : 
                        ((ptrdiff_t)rank * (ptrdiff_t)late_blockcount + split_rank));
        block_count = ((rank < split_rank)? early_blockcount : late_blockcount);
        COLL_TUNED_COMPUTE_BLOCKCOUNT(block_count, num_phases, split_phase,
                                      early_phase_segcount, late_phase_segcount)
            phase_count = ((phase < split_phase)?
                           (early_phase_segcount) : (late_phase_segcount));
        phase_offset = ((phase < split_phase)?
                        ((ptrdiff_t)phase * (ptrdiff_t)early_phase_segcount) : 
                        ((ptrdiff_t)phase * (ptrdiff_t)late_phase_segcount + split_phase));
        tmpsend = ((char*)rbuf) + (ptrdiff_t)(block_offset + phase_offset) * extent;
        ret = MCA_PML_CALL(send(tmpsend, phase_count, dtype, send_to,
                                MCA_COLL_BASE_TAG_ALLREDUCE,
                                MCA_PML_BASE_SEND_STANDARD, comm));
        if (MPI_SUCCESS != ret) { line = __LINE__; goto error_hndl; }
      
        for (k = 2; k < size; k++) {
            const int prevblock = (rank + size - k + 1) % size;
         
            inbi = inbi ^ 0x1;
         
            /* Post irecv for the current block */
            ret = MCA_PML_CALL(irecv(inbuf[inbi], max_segcount, dtype, recv_from,
                                     MCA_COLL_BASE_TAG_ALLREDUCE, comm, 
                                     &reqs[inbi]));
            if (MPI_SUCCESS != ret) { line = __LINE__; goto error_hndl; }
         
            /* Wait on previous block to arrive */
            ret = ompi_request_wait(&reqs[inbi ^ 0x1], MPI_STATUS_IGNORE);
            if (MPI_SUCCESS != ret) { line = __LINE__; goto error_hndl; }
         
            /* Apply operation on previous block: result goes to rbuf
               rbuf[prevblock] = inbuf[inbi ^ 0x1] (op) rbuf[prevblock]
            */
            block_offset = ((prevblock < split_rank)?
                            ((ptrdiff_t)prevblock * (ptrdiff_t)early_blockcount) :
                            ((ptrdiff_t)prevblock * (ptrdiff_t)late_blockcount + split_rank));
            block_count = ((prevblock < split_rank)? 
                           early_blockcount : late_blockcount);
            COLL_TUNED_COMPUTE_BLOCKCOUNT(block_count, num_phases, split_phase,
                                          early_phase_segcount, late_phase_segcount)
                phase_count = ((phase < split_phase)?
                               (early_phase_segcount) : (late_phase_segcount));
            phase_offset = ((phase < split_phase)?
                            ((ptrdiff_t)phase * (ptrdiff_t)early_phase_segcount) : 
                            ((ptrdiff_t)phase * (ptrdiff_t)late_phase_segcount + split_phase));
            tmprecv = ((char*)rbuf) + (ptrdiff_t)(block_offset + phase_offset) * extent;
            ompi_op_reduce(op, inbuf[inbi ^ 0x1], tmprecv, phase_count, dtype);
         
            /* send previous block to send_to */
            ret = MCA_PML_CALL(send(tmprecv, phase_count, dtype, send_to,
                                    MCA_COLL_BASE_TAG_ALLREDUCE,
                                    MCA_PML_BASE_SEND_STANDARD, comm));
            if (MPI_SUCCESS != ret) { line = __LINE__; goto error_hndl; }
        }
      
        /* Wait on the last block to arrive */
        ret = ompi_request_wait(&reqs[inbi], MPI_STATUS_IGNORE);
        if (MPI_SUCCESS != ret) { line = __LINE__; goto error_hndl; }
      
        /* Apply operation on the last block (from neighbor (rank + 1) 
           rbuf[rank+1] = inbuf[inbi] (op) rbuf[rank + 1] */
        recv_from = (rank + 1) % size;
        block_offset = ((recv_from < split_rank)?
                        ((ptrdiff_t)recv_from * (ptrdiff_t)early_blockcount) :
                        ((ptrdiff_t)recv_from * (ptrdiff_t)late_blockcount + split_rank));
        block_count = ((recv_from < split_rank)? 
                       early_blockcount : late_blockcount);
        COLL_TUNED_COMPUTE_BLOCKCOUNT(block_count, num_phases, split_phase,
                                      early_phase_segcount, late_phase_segcount)
            phase_count = ((phase < split_phase)?
                           (early_phase_segcount) : (late_phase_segcount));
        phase_offset = ((phase < split_phase)?
                        ((ptrdiff_t)phase * (ptrdiff_t)early_phase_segcount) : 
                        ((ptrdiff_t)phase * (ptrdiff_t)late_phase_segcount + split_phase));
        tmprecv = ((char*)rbuf) + (ptrdiff_t)(block_offset + phase_offset) * extent;
        ompi_op_reduce(op, inbuf[inbi], tmprecv, phase_count, dtype);
    }

    /* Distribution loop - variation of ring allgather */
    send_to = (rank + 1) % size;
    recv_from = (rank + size - 1) % size;
    for (k = 0; k < size - 1; k++) {
        const int recv_data_from = (rank + size - k) % size;
        const int send_data_from = (rank + 1 + size - k) % size;
        const int send_block_offset = 
            ((send_data_from < split_rank)?
             ((ptrdiff_t)send_data_from * (ptrdiff_t)early_blockcount) :
             ((ptrdiff_t)send_data_from * (ptrdiff_t)late_blockcount + split_rank));
        const int recv_block_offset = 
            ((recv_data_from < split_rank)?
             ((ptrdiff_t)recv_data_from * (ptrdiff_t)early_blockcount) :
             ((ptrdiff_t)recv_data_from * (ptrdiff_t)late_blockcount + split_rank));
        block_count = ((send_data_from < split_rank)? 
                       early_blockcount : late_blockcount);

        tmprecv = (char*)rbuf + (ptrdiff_t)recv_block_offset * extent;
        tmpsend = (char*)rbuf + (ptrdiff_t)send_block_offset * extent;

        ret = ompi_coll_tuned_sendrecv(tmpsend, block_count, dtype, send_to,
                                       MCA_COLL_BASE_TAG_ALLREDUCE,
                                       tmprecv, early_blockcount, dtype, recv_from,
                                       MCA_COLL_BASE_TAG_ALLREDUCE,
                                       comm, MPI_STATUS_IGNORE, rank);
        if (MPI_SUCCESS != ret) { line = __LINE__; goto error_hndl;}

    }

    if (NULL != inbuf[0]) free(inbuf[0]);
    if (NULL != inbuf[1]) free(inbuf[1]);

    return MPI_SUCCESS;

 error_hndl:
    OPAL_OUTPUT((ompi_coll_tuned_stream, "%s:%4d\tRank %d Error occurred %d\n",
                 __FILE__, line, rank, ret));
    if (NULL != inbuf[0]) free(inbuf[0]);
    if (NULL != inbuf[1]) free(inbuf[1]);
    return ret;
}

/*
 * 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 tuned/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 */


/*
 *	allreduce_intra
 *
 *	Function:	- allreduce using other MPI collectives
 *	Accepts:	- same as MPI_Allreduce()
 *	Returns:	- MPI_SUCCESS or error code
 */
int
ompi_coll_tuned_allreduce_intra_basic_linear(void *sbuf, void *rbuf, int count,
                                             struct ompi_datatype_t *dtype,
                                             struct ompi_op_t *op,
                                             struct ompi_communicator_t *comm,
                                             mca_coll_base_module_t *module)
{
    int err, rank;

    rank = ompi_comm_rank(comm);

    OPAL_OUTPUT((ompi_coll_tuned_stream,"coll:tuned:allreduce_intra_basic_linear rank %d", rank));

    /* Reduce to 0 and broadcast. */

    if (MPI_IN_PLACE == sbuf) {
        if (0 == rank) {
            err = ompi_coll_tuned_reduce_intra_basic_linear (MPI_IN_PLACE, rbuf, count, dtype,
                                                             op, 0, comm, module);
        } else {
            err = ompi_coll_tuned_reduce_intra_basic_linear(rbuf, NULL, count, dtype,
                                                            op, 0, comm, module);
        }
    } else {
        err = ompi_coll_tuned_reduce_intra_basic_linear(sbuf, rbuf, count, dtype,
                                                        op, 0, comm, module);
    }
    if (MPI_SUCCESS != err) {
        return err;
    }

    return ompi_coll_tuned_bcast_intra_basic_linear(rbuf, count, dtype, 0, comm, module);
}


/* copied function (with appropriate renaming) ends here */

/* The following are used by dynamic and forced rules */

/* publish details of each algorithm and if its forced/fixed/locked in */
/* as you add methods/algorithms you must update this and the query/map routines */

/* this routine is called by the component only */
/* this makes sure that the mca parameters are set to their initial values and perms */
/* module does not call this they call the forced_getvalues routine instead */

int ompi_coll_tuned_allreduce_intra_check_forced_init (coll_tuned_force_algorithm_mca_param_indices_t *mca_param_indices)
{
    mca_base_var_enum_t *new_enum;

    ompi_coll_tuned_forced_max_algorithms[ALLREDUCE] = coll_tuned_allreduce_algorithm_count;

    (void) mca_base_component_var_register(&mca_coll_tuned_component.super.collm_version,
                                           "allreduce_algorithm_count",
                                           "Number of allreduce algorithms available",
                                           MCA_BASE_VAR_TYPE_INT, NULL, 0,
                                           MCA_BASE_VAR_FLAG_DEFAULT_ONLY,
                                           OPAL_INFO_LVL_5,
                                           MCA_BASE_VAR_SCOPE_CONSTANT,
                                           &coll_tuned_allreduce_algorithm_count);

    /* MPI_T: This variable should eventually be bound to a communicator */
    coll_tuned_allreduce_forced_algorithm = 0;
    (void) mca_base_var_enum_create("coll_tuned_allreduce_algorithms", allreduce_algorithms, &new_enum);
    mca_param_indices->algorithm_param_index =
        mca_base_component_var_register(&mca_coll_tuned_component.super.collm_version,
                                        "allreduce_algorithm",
                                        "Which allreduce algorithm is used. Can be locked down to any of: 0 ignore, 1 basic linear, 2 nonoverlapping (tuned reduce + tuned bcast), 3 recursive doubling, 4 ring, 5 segmented ring",
                                        MCA_BASE_VAR_TYPE_INT, new_enum, 0, 0,
                                        OPAL_INFO_LVL_5,
                                        MCA_BASE_VAR_SCOPE_READONLY,
                                        &coll_tuned_allreduce_forced_algorithm);
    OBJ_RELEASE(new_enum);
    if (mca_param_indices->algorithm_param_index < 0) {
        return mca_param_indices->algorithm_param_index;
    }

    coll_tuned_allreduce_segment_size = 0;
    mca_param_indices->segsize_param_index =
        mca_base_component_var_register(&mca_coll_tuned_component.super.collm_version,
                                        "allreduce_algorithm_segmentsize",
                                        "Segment size in bytes used by default for allreduce algorithms. Only has meaning if algorithm is forced and supports segmenting. 0 bytes means no segmentation.",
                                        MCA_BASE_VAR_TYPE_INT, NULL, 0, 0,
                                        OPAL_INFO_LVL_5,
                                        MCA_BASE_VAR_SCOPE_READONLY,
                                        &coll_tuned_allreduce_segment_size);

    coll_tuned_allreduce_tree_fanout = ompi_coll_tuned_init_tree_fanout; /* get system wide default */
    mca_param_indices->tree_fanout_param_index =
        mca_base_component_var_register(&mca_coll_tuned_component.super.collm_version,
                                        "allreduce_algorithm_tree_fanout",
                                        "Fanout for n-tree used for allreduce algorithms. Only has meaning if algorithm is forced and supports n-tree topo based operation.",
                                        MCA_BASE_VAR_TYPE_INT, NULL, 0, 0,
                                        OPAL_INFO_LVL_5,
                                        MCA_BASE_VAR_SCOPE_READONLY,
                                        &coll_tuned_allreduce_tree_fanout);

    coll_tuned_allreduce_chain_fanout = ompi_coll_tuned_init_chain_fanout; /* get system wide default */
    mca_param_indices->chain_fanout_param_index = 
      mca_base_component_var_register(&mca_coll_tuned_component.super.collm_version,
                                      "allreduce_algorithm_chain_fanout",
                                      "Fanout for chains used for allreduce algorithms. Only has meaning if algorithm is forced and supports chain topo based operation.",
                                      MCA_BASE_VAR_TYPE_INT, NULL, 0, 0,
                                      OPAL_INFO_LVL_5,
                                      MCA_BASE_VAR_SCOPE_READONLY,
                                      &coll_tuned_allreduce_chain_fanout);

    return (MPI_SUCCESS);
}


int ompi_coll_tuned_allreduce_intra_do_forced(void *sbuf, void *rbuf, int count,
                                              struct ompi_datatype_t *dtype,
                                              struct ompi_op_t *op,
                                              struct ompi_communicator_t *comm,
                                              mca_coll_base_module_t *module)
{
    mca_coll_tuned_module_t *tuned_module = (mca_coll_tuned_module_t*) module;
    mca_coll_tuned_comm_t *data = tuned_module->tuned_data;

    OPAL_OUTPUT((ompi_coll_tuned_stream,"coll:tuned:allreduce_intra_do_forced selected algorithm %d, segment size %d", 
                 data->user_forced[ALLREDUCE].algorithm,
                 data->user_forced[ALLREDUCE].segsize));

    switch (data->user_forced[ALLREDUCE].algorithm) {
    case (0):  return ompi_coll_tuned_allreduce_intra_dec_fixed (sbuf, rbuf, count, dtype, op, comm, module);
    case (1):  return ompi_coll_tuned_allreduce_intra_basic_linear (sbuf, rbuf, count, dtype, op, comm, module);
    case (2):  return ompi_coll_tuned_allreduce_intra_nonoverlapping (sbuf, rbuf, count, dtype, op, comm, module);
    case (3):  return ompi_coll_tuned_allreduce_intra_recursivedoubling (sbuf, rbuf, count, dtype, op, comm, module);
    case (4):  return ompi_coll_tuned_allreduce_intra_ring (sbuf, rbuf, count, dtype, op, comm, module);
    case (5):  return ompi_coll_tuned_allreduce_intra_ring_segmented (sbuf, rbuf, count, dtype, op, comm, module, data->user_forced[ALLREDUCE].segsize);
    default:
        OPAL_OUTPUT((ompi_coll_tuned_stream,"coll:tuned:allreduce_intra_do_forced attempt to select algorithm %d when only 0-%d is valid?",
                     data->user_forced[ALLREDUCE].algorithm, 
                     ompi_coll_tuned_forced_max_algorithms[ALLREDUCE]));
        return (MPI_ERR_ARG);
    } /* switch */

}


int ompi_coll_tuned_allreduce_intra_do_this(void *sbuf, void *rbuf, int count,
                                            struct ompi_datatype_t *dtype,
                                            struct ompi_op_t *op,
                                            struct ompi_communicator_t *comm,
                                            mca_coll_base_module_t *module,
                                            int algorithm, int faninout, int segsize)
{
    OPAL_OUTPUT((ompi_coll_tuned_stream,"coll:tuned:allreduce_intra_do_this algorithm %d topo fan in/out %d segsize %d", 
                 algorithm, faninout, segsize));

    switch (algorithm) {
    case (0):   return ompi_coll_tuned_allreduce_intra_dec_fixed (sbuf, rbuf, count, dtype, op, comm, module);
    case (1):   return ompi_coll_tuned_allreduce_intra_basic_linear (sbuf, rbuf, count, dtype, op, comm, module);
    case (2):   return ompi_coll_tuned_allreduce_intra_nonoverlapping (sbuf, rbuf, count, dtype, op, comm, module);
    case (3):   return ompi_coll_tuned_allreduce_intra_recursivedoubling (sbuf, rbuf, count, dtype, op, comm, module);
    case (4):   return ompi_coll_tuned_allreduce_intra_ring (sbuf, rbuf, count, dtype, op, comm, module);
    case (5):   return ompi_coll_tuned_allreduce_intra_ring_segmented (sbuf, rbuf, count, dtype, op, comm, module, segsize);
    default:
        OPAL_OUTPUT((ompi_coll_tuned_stream,"coll:tuned:allreduce_intra_do_this attempt to select algorithm %d when only 0-%d is valid?",
                     algorithm, ompi_coll_tuned_forced_max_algorithms[ALLREDUCE]));
        return (MPI_ERR_ARG);
    } /* switch */

}