openmpi/ompi/mca/coll/tuned/coll_tuned_reduce_scatter.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) 2008      Sun Microsystems, Inc.  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"

/* reduce_scatter algorithm variables */
static int coll_tuned_reduce_scatter_algorithm_count = 2;
static int coll_tuned_reduce_scatter_forced_algorithm = 0;
static int coll_tuned_reduce_scatter_segment_size = 0;
static int coll_tuned_reduce_scatter_tree_fanout;
static int coll_tuned_reduce_scatter_chain_fanout;

/* valid values for coll_tuned_reduce_scatter_forced_algorithm */
static mca_base_var_enum_value_t reduce_scatter_algorithms[] = {
    {0, "ignore"},
    {1, "non-overlapping"},
    {2, "recursive_halfing"},
    {3, "ring"},
    {0, NULL}
};

/*******************************************************************************
 * ompi_coll_tuned_reduce_scatter_intra_nonoverlapping
 *
 * This function just calls a reduce to rank 0, followed by an 
 * appropriate scatterv call.
 */
int ompi_coll_tuned_reduce_scatter_intra_nonoverlapping(void *sbuf, void *rbuf, 
                                                        int *rcounts,
                                                        struct ompi_datatype_t *dtype,
                                                        struct ompi_op_t *op,
                                                        struct ompi_communicator_t *comm,
                                                        mca_coll_base_module_t *module) 
{
    int err, i, rank, size, total_count, *displs = NULL;
    const int root = 0;
    char *tmprbuf = NULL, *tmprbuf_free = NULL;

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

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

    for (i = 0, total_count = 0; i < size; i++) { total_count += rcounts[i]; }

    /* Reduce to rank 0 (root) and scatterv */
    tmprbuf = (char*) rbuf;
    if (MPI_IN_PLACE == sbuf) {
        /* rbuf on root (0) is big enough to hold whole data */
        if (root == rank) {
            err = comm->c_coll.coll_reduce (MPI_IN_PLACE, tmprbuf, total_count, 
                                            dtype, op, root, comm, comm->c_coll.coll_reduce_module);
        } else {
            err = comm->c_coll.coll_reduce(tmprbuf, NULL, total_count,
                                           dtype, op, root, comm, comm->c_coll.coll_reduce_module);
        }
    } else {
        if (root == rank) {
            /* We must allocate temporary receive buffer on root to ensure that
               rbuf is big enough */
            ptrdiff_t lb, extent, tlb, textent;
         
            ompi_datatype_get_extent(dtype, &lb, &extent);
            ompi_datatype_get_true_extent(dtype, &tlb, &textent);

            tmprbuf_free = (char*) malloc(textent + (ptrdiff_t)(total_count - 1) * extent);
            tmprbuf = tmprbuf_free - lb;
        } 
        err = comm->c_coll.coll_reduce (sbuf, tmprbuf, total_count,
                                        dtype, op, root, comm, comm->c_coll.coll_reduce_module);
    }
    if (MPI_SUCCESS != err) {
        if (NULL != tmprbuf_free) free(tmprbuf_free);
        return err;
    }
 
    displs = (int*) malloc(size * sizeof(int));
    displs[0] = 0;
    for (i = 1; i < size; i++) {
        displs[i] = displs[i-1] + rcounts[i-1];
    }
    err =  comm->c_coll.coll_scatterv (tmprbuf, rcounts, displs, dtype,
                                       rbuf, rcounts[rank], dtype,
                                       root, comm, comm->c_coll.coll_scatterv_module);
    free(displs);
    if (NULL != tmprbuf_free) free(tmprbuf_free);

    return err;
}

/*
 * Recursive-halving function is (*mostly*) copied from the BASIC coll module.
 * I have removed the part which handles "large" message sizes 
 * (non-overlapping version of reduce_Scatter).
 */

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

/*
 *  reduce_scatter_intra_basic_recursivehalving
 *
 *  Function:   - reduce scatter implementation using recursive-halving 
 *                algorithm
 *  Accepts:    - same as MPI_Reduce_scatter()
 *  Returns:    - MPI_SUCCESS or error code
 *  Limitation: - Works only for commutative operations.
 */
int
ompi_coll_tuned_reduce_scatter_intra_basic_recursivehalving(void *sbuf, 
                                                            void *rbuf, 
                                                            int *rcounts,
                                                            struct ompi_datatype_t *dtype,
                                                            struct ompi_op_t *op,
                                                            struct ompi_communicator_t *comm,
                                                            mca_coll_base_module_t *module)
{
    int i, rank, size, count, err = OMPI_SUCCESS;
    int tmp_size, remain = 0, tmp_rank, *disps = NULL;
    ptrdiff_t true_lb, true_extent, lb, extent, buf_size;
    char *recv_buf = NULL, *recv_buf_free = NULL;
    char *result_buf = NULL, *result_buf_free = NULL;
   
    /* Initialize */
    rank = ompi_comm_rank(comm);
    size = ompi_comm_size(comm);
   
    OPAL_OUTPUT((ompi_coll_tuned_stream,"coll:tuned:reduce_scatter_intra_basic_recursivehalving, rank %d", rank));

    /* Find displacements and the like */
    disps = (int*) malloc(sizeof(int) * size);
    if (NULL == disps) return OMPI_ERR_OUT_OF_RESOURCE;

    disps[0] = 0;
    for (i = 0; i < (size - 1); ++i) {
        disps[i + 1] = disps[i] + rcounts[i];
    }
    count = disps[size - 1] + rcounts[size - 1];

    /* short cut the trivial case */
    if (0 == count) {
        free(disps);
        return OMPI_SUCCESS;
    }

    /* get datatype information */
    ompi_datatype_get_extent(dtype, &lb, &extent);
    ompi_datatype_get_true_extent(dtype, &true_lb, &true_extent);
    buf_size = true_extent + (ptrdiff_t)(count - 1) * extent;

    /* Handle MPI_IN_PLACE */
    if (MPI_IN_PLACE == sbuf) {
        sbuf = rbuf;
    }

    /* Allocate temporary receive buffer. */
    recv_buf_free = (char*) malloc(buf_size);
    recv_buf = recv_buf_free - lb;
    if (NULL == recv_buf_free) {
        err = OMPI_ERR_OUT_OF_RESOURCE;
        goto cleanup;
    }
   
    /* allocate temporary buffer for results */
    result_buf_free = (char*) malloc(buf_size);
    result_buf = result_buf_free - lb;
   
    /* copy local buffer into the temporary results */
    err = ompi_datatype_sndrcv(sbuf, count, dtype, result_buf, count, dtype);
    if (OMPI_SUCCESS != err) goto cleanup;
   
    /* figure out power of two mapping: grow until larger than
       comm size, then go back one, to get the largest power of
       two less than comm size */
    tmp_size = opal_next_poweroftwo (size); 
    tmp_size >>= 1;
    remain = size - tmp_size;
   
    /* If comm size is not a power of two, have the first "remain"
       procs with an even rank send to rank + 1, leaving a power of
       two procs to do the rest of the algorithm */
    if (rank < 2 * remain) {
        if ((rank & 1) == 0) {
            err = MCA_PML_CALL(send(result_buf, count, dtype, rank + 1, 
                                    MCA_COLL_BASE_TAG_REDUCE_SCATTER,
                                    MCA_PML_BASE_SEND_STANDARD,
                                    comm));
            if (OMPI_SUCCESS != err) goto cleanup;
         
            /* we don't participate from here on out */
            tmp_rank = -1;
        } else {
            err = MCA_PML_CALL(recv(recv_buf, count, dtype, rank - 1,
                                    MCA_COLL_BASE_TAG_REDUCE_SCATTER,
                                    comm, MPI_STATUS_IGNORE));
         
            /* integrate their results into our temp results */
            ompi_op_reduce(op, recv_buf, result_buf, count, dtype);
         
            /* adjust rank to be the bottom "remain" ranks */
            tmp_rank = rank / 2;
        }
    } else {
        /* just need to adjust rank to show that the bottom "even
           remain" ranks dropped out */
        tmp_rank = rank - remain;
    }
   
    /* For ranks not kicked out by the above code, perform the
       recursive halving */
    if (tmp_rank >= 0) {
        int *tmp_disps = NULL, *tmp_rcounts = NULL;
        int mask, send_index, recv_index, last_index;
      
        /* recalculate disps and rcounts to account for the
           special "remainder" processes that are no longer doing
           anything */
        tmp_rcounts = (int*) malloc(tmp_size * sizeof(int));
        if (NULL == tmp_rcounts) {
            err = OMPI_ERR_OUT_OF_RESOURCE;
            goto cleanup;
        }
        tmp_disps = (int*) malloc(tmp_size * sizeof(int));
        if (NULL == tmp_disps) {
            free(tmp_rcounts);
            err = OMPI_ERR_OUT_OF_RESOURCE;
            goto cleanup;
        }

        for (i = 0 ; i < tmp_size ; ++i) {
            if (i < remain) {
                /* need to include old neighbor as well */
                tmp_rcounts[i] = rcounts[i * 2 + 1] + rcounts[i * 2];
            } else {
                tmp_rcounts[i] = rcounts[i + remain];
            }
        }

        tmp_disps[0] = 0;
        for (i = 0; i < tmp_size - 1; ++i) {
            tmp_disps[i + 1] = tmp_disps[i] + tmp_rcounts[i];
        }

        /* do the recursive halving communication.  Don't use the
           dimension information on the communicator because I
           think the information is invalidated by our "shrinking"
           of the communicator */
        mask = tmp_size >> 1;
        send_index = recv_index = 0;
        last_index = tmp_size;
        while (mask > 0) {
            int tmp_peer, peer, send_count, recv_count;
            struct ompi_request_t *request;

            tmp_peer = tmp_rank ^ mask;
            peer = (tmp_peer < remain) ? tmp_peer * 2 + 1 : tmp_peer + remain;

            /* figure out if we're sending, receiving, or both */
            send_count = recv_count = 0;
            if (tmp_rank < tmp_peer) {
                send_index = recv_index + mask;
                for (i = send_index ; i < last_index ; ++i) {
                    send_count += tmp_rcounts[i];
                }
                for (i = recv_index ; i < send_index ; ++i) {
                    recv_count += tmp_rcounts[i];
                }
            } else {
                recv_index = send_index + mask;
                for (i = send_index ; i < recv_index ; ++i) {
                    send_count += tmp_rcounts[i];
                }
                for (i = recv_index ; i < last_index ; ++i) {
                    recv_count += tmp_rcounts[i];
                }
            }

            /* actual data transfer.  Send from result_buf,
               receive into recv_buf */
            if (recv_count > 0) {
                err = MCA_PML_CALL(irecv(recv_buf + (ptrdiff_t)tmp_disps[recv_index] * extent,
                                         recv_count, dtype, peer,
                                         MCA_COLL_BASE_TAG_REDUCE_SCATTER,
                                         comm, &request));
                if (OMPI_SUCCESS != err) {
                    free(tmp_rcounts);
                    free(tmp_disps);
                    goto cleanup;
                }                                             
            }
            if (send_count > 0) {
                err = MCA_PML_CALL(send(result_buf + (ptrdiff_t)tmp_disps[send_index] * extent,
                                        send_count, dtype, peer, 
                                        MCA_COLL_BASE_TAG_REDUCE_SCATTER,
                                        MCA_PML_BASE_SEND_STANDARD,
                                        comm));
                if (OMPI_SUCCESS != err) {
                    free(tmp_rcounts);
                    free(tmp_disps);
                    goto cleanup;
                }                                             
            }

            /* if we received something on this step, push it into
               the results buffer */
            if (recv_count > 0) {
                err = ompi_request_wait(&request, MPI_STATUS_IGNORE);
                if (OMPI_SUCCESS != err) {
                    free(tmp_rcounts);
                    free(tmp_disps);
                    goto cleanup;
                }                                             

                ompi_op_reduce(op, 
                               recv_buf + (ptrdiff_t)tmp_disps[recv_index] * extent, 
                               result_buf + (ptrdiff_t)tmp_disps[recv_index] * extent,
                               recv_count, dtype);
            }

            /* update for next iteration */
            send_index = recv_index;
            last_index = recv_index + mask;
            mask >>= 1;
        }

        /* copy local results from results buffer into real receive buffer */
        if (0 != rcounts[rank]) {
            err = ompi_datatype_sndrcv(result_buf + disps[rank] * extent,
                                       rcounts[rank], dtype, 
                                       rbuf, rcounts[rank], dtype);
            if (OMPI_SUCCESS != err) {
                free(tmp_rcounts);
                free(tmp_disps);
                goto cleanup;
            }                                             
        }

        free(tmp_rcounts);
        free(tmp_disps);
    }

    /* Now fix up the non-power of two case, by having the odd
       procs send the even procs the proper results */
    if (rank < (2 * remain)) {
        if ((rank & 1) == 0) {
            if (rcounts[rank]) {
                err = MCA_PML_CALL(recv(rbuf, rcounts[rank], dtype, rank + 1,
                                        MCA_COLL_BASE_TAG_REDUCE_SCATTER,
                                        comm, MPI_STATUS_IGNORE));
                if (OMPI_SUCCESS != err) goto cleanup;
            }
        } else {
            if (rcounts[rank - 1]) {
                err = MCA_PML_CALL(send(result_buf + disps[rank - 1] * extent,
                                        rcounts[rank - 1], dtype, rank - 1,
                                        MCA_COLL_BASE_TAG_REDUCE_SCATTER,
                                        MCA_PML_BASE_SEND_STANDARD,
                                        comm));
                if (OMPI_SUCCESS != err) goto cleanup;
            }
        }            
    }

 cleanup:
    if (NULL != disps) free(disps);
    if (NULL != recv_buf_free) free(recv_buf_free);
    if (NULL != result_buf_free) free(result_buf_free);

    return err;
}

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


/*
 *   ompi_coll_tuned_reduce_scatter_intra_ring
 *
 *   Function:       Ring algorithm for reduce_scatter operation
 *   Accepts:        Same as MPI_Reduce_scatter()
 *   Returns:        MPI_SUCCESS or error code
 *
 *   Description:    Implements ring algorithm for reduce_scatter: 
 *                   the block sizes defined in rcounts are exchanged and 
 8                    updated until they reach proper destination.
 *                   Algorithm requires 2 * max(rcounts) extra buffering
 *
 *   Limitations:    The algorithm DOES NOT preserve order of operations so it 
 *                   can be used only for commutative operations.
 *         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-1) to rank (r+1) and 
 *                 receives block (r+1) from rank (r-1) [with wraparound].
 *   #      0              1             2              3             4
 *        [00]           [10]        [10+20]   ->     [30]           [40]
 *        [01]           [11]          [21]          [21+31]  ->     [41]
 *    ->  [02]           [12]          [22]           [32]         [32+42] -->..
 *      [43+03] ->       [13]          [23]           [33]           [43]
 *        [04]         [04+14]  ->     [24]           [34]           [44]
 *         
 *         Step 1:
 *   #      0              1             2              3             4
 *        [00]           [10]        [10+20]       [10+20+30] ->     [40]
 *    ->  [01]           [11]          [21]          [21+31]      [21+31+41] ->
 *     [32+42+02] ->     [12]          [22]           [32]         [32+42] 
 *        [03]        [43+03+13] ->    [23]           [33]           [43]
 *        [04]         [04+14]      [04+14+24]  ->    [34]           [44]
 *
 *         Step 2:
 *   #      0              1             2              3             4
 *     -> [00]           [10]        [10+20]       [10+20+30]   [10+20+30+40] ->
 *   [21+31+41+01]->     [11]          [21]          [21+31]      [21+31+41]
 *     [32+42+02]   [32+42+02+12]->    [22]           [32]         [32+42] 
 *        [03]        [43+03+13]   [43+03+13+23]->    [33]           [43]
 *        [04]         [04+14]      [04+14+24]    [04+14+24+34] ->   [44]
 *
 *         Step 3:
 *   #      0             1              2              3             4
 * [10+20+30+40+00]     [10]         [10+20]       [10+20+30]   [10+20+30+40]
 *  [21+31+41+01] [21+31+41+01+11]     [21]          [21+31]      [21+31+41]
 *    [32+42+02]   [32+42+02+12] [32+42+02+12+22]     [32]         [32+42] 
 *       [03]        [43+03+13]    [43+03+13+23] [43+03+13+23+33]    [43]
 *       [04]         [04+14]       [04+14+24]    [04+14+24+34] [04+14+24+34+44]
 *    DONE :)
 *
 */
int 
ompi_coll_tuned_reduce_scatter_intra_ring(void *sbuf, void *rbuf, int *rcounts,
                                          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, i, k, recv_from, send_to, total_count, max_block_count;
    int inbi, *displs = NULL;
    char *tmpsend = NULL, *tmprecv = NULL, *accumbuf = NULL, *accumbuf_free = NULL;
    char *inbuf_free[2] = {NULL, NULL}, *inbuf[2] = {NULL, NULL};
    ptrdiff_t true_lb, true_extent, lb, extent, max_real_segsize;
    ompi_request_t *reqs[2] = {NULL, NULL};
    size_t typelng;

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

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

    /* Determine the maximum number of elements per node, 
       corresponding block size, and displacements array.
    */
    displs = (int*) malloc(size * sizeof(int));
    if (NULL == displs) { ret = -1; line = __LINE__; goto error_hndl; }
    displs[0] = 0;
    total_count = rcounts[0];
    max_block_count = rcounts[0];
    for (i = 1; i < size; i++) { 
        displs[i] = total_count;
        total_count += rcounts[i];
        if (max_block_count < rcounts[i]) max_block_count = rcounts[i];
    }
      
    /* Special case for size == 1 */
    if (1 == size) {
        if (MPI_IN_PLACE != sbuf) {
            ret = ompi_datatype_copy_content_same_ddt(dtype, total_count, 
                                                      (char*)rbuf, (char*)sbuf);
            if (ret < 0) { line = __LINE__; goto error_hndl; }
        }
        free(displs);
        return MPI_SUCCESS;
    }

    /* Allocate and initialize temporary buffers, we need:
       - a temporary buffer to perform reduction (size total_count) since
       rbuf can be of rcounts[rank] size.
       - up to two temporary buffers used for communication/computation overlap.
    */
    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; }

    max_real_segsize = true_extent + (ptrdiff_t)(max_block_count - 1) * extent;

    accumbuf_free = (char*)malloc(true_extent + (ptrdiff_t)(total_count - 1) * extent);
    if (NULL == accumbuf_free) { ret = -1; line = __LINE__; goto error_hndl; }
    accumbuf = accumbuf_free - lb;

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

    /* Handle MPI_IN_PLACE for size > 1 */
    if (MPI_IN_PLACE == sbuf) {
        sbuf = rbuf;
    }

    ret = ompi_datatype_copy_content_same_ddt(dtype, total_count, 
                                              accumbuf, (char*)sbuf);
    if (ret < 0) { line = __LINE__; goto error_hndl; }

    /* Computation loop */

    /* 
       For each of the remote nodes:
       - post irecv for block (r-2) from (r-1) with wrap around
       - send block (r-1) to (r+1)
       - in loop for every step k = 2 .. n
       - post irecv for block (r - 1 + n - k) % n
       - wait on block (r + n - k) % n to arrive
       - compute on block (r + n - k ) % n
       - send block (r + n - k) % n
       - wait on block (r)
       - compute on block (r)
       - copy block (r) to rbuf
       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_block_count, dtype, recv_from,
                             MCA_COLL_BASE_TAG_REDUCE_SCATTER, comm, 
                             &reqs[inbi]));
    if (MPI_SUCCESS != ret) { line = __LINE__; goto error_hndl; }
    tmpsend = accumbuf + (ptrdiff_t)displs[recv_from] * extent;
    ret = MCA_PML_CALL(send(tmpsend, rcounts[recv_from], dtype, send_to,
                            MCA_COLL_BASE_TAG_REDUCE_SCATTER,
                            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) % size;
      
        inbi = inbi ^ 0x1;

        /* Post irecv for the current block */
        ret = MCA_PML_CALL(irecv(inbuf[inbi], max_block_count, dtype, recv_from,
                                 MCA_COLL_BASE_TAG_REDUCE_SCATTER, 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]
        */
        tmprecv = accumbuf + (ptrdiff_t)displs[prevblock] * extent;
        ompi_op_reduce(op, inbuf[inbi ^ 0x1], tmprecv, rcounts[prevblock], dtype);
      
        /* send previous block to send_to */
        ret = MCA_PML_CALL(send(tmprecv, rcounts[prevblock], dtype, send_to,
                                MCA_COLL_BASE_TAG_REDUCE_SCATTER,
                                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 (my block)
       rbuf[rank] = inbuf[inbi] (op) rbuf[rank] */
    tmprecv = accumbuf + (ptrdiff_t)displs[rank] * extent;
    ompi_op_reduce(op, inbuf[inbi], tmprecv, rcounts[rank], dtype);
   
    /* Copy result from tmprecv to rbuf */
    ret = ompi_datatype_copy_content_same_ddt(dtype, rcounts[rank], (char *)rbuf, tmprecv);
    if (ret < 0) { line = __LINE__; goto error_hndl; }

    if (NULL != displs) free(displs);
    if (NULL != accumbuf_free) free(accumbuf_free);
    if (NULL != inbuf_free[0]) free(inbuf_free[0]);
    if (NULL != inbuf_free[1]) free(inbuf_free[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 != displs) free(displs);
    if (NULL != accumbuf_free) free(accumbuf_free);
    if (NULL != inbuf_free[0]) free(inbuf_free[0]);
    if (NULL != inbuf_free[1]) free(inbuf_free[1]);
    return ret;
}


/**
 * 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_reduce_scatter_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[REDUCESCATTER] = coll_tuned_reduce_scatter_algorithm_count;

    (void) mca_base_component_var_register(&mca_coll_tuned_component.super.collm_version,
                                           "reduce_scatter_algorithm_count",
                                           "Number of reduce_scatter 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_reduce_scatter_algorithm_count);

    /* MPI_T: This variable should eventually be bound to a communicator */
    coll_tuned_reduce_scatter_forced_algorithm = 0;
    (void) mca_base_var_enum_create("coll_tuned_reduce_scatter_algorithms", reduce_scatter_algorithms, &new_enum);
    mca_param_indices->algorithm_param_index =
        mca_base_component_var_register(&mca_coll_tuned_component.super.collm_version,
                                        "reduce_scatter_algorithm",
                                        "Which reduce reduce_scatter algorithm is used. Can be locked down to choice of: 0 ignore, 1 non-overlapping (Reduce + Scatterv), 2 recursive halving, 3 ring",
                                        MCA_BASE_VAR_TYPE_INT, new_enum, 0, 0,
                                        OPAL_INFO_LVL_5,
                                        MCA_BASE_VAR_SCOPE_READONLY,
                                        &coll_tuned_reduce_scatter_forced_algorithm);
    OBJ_RELEASE(new_enum);
    if (mca_param_indices->algorithm_param_index < 0) {
        return mca_param_indices->algorithm_param_index;
    }

    coll_tuned_reduce_scatter_segment_size = 0;
    mca_param_indices->segsize_param_index =
        mca_base_component_var_register(&mca_coll_tuned_component.super.collm_version,
                                        "reduce_scatter_algorithm_segmentsize",
                                        "Segment size in bytes used by default for reduce_scatter 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_reduce_scatter_segment_size);

    coll_tuned_reduce_scatter_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,
                                        "reduce_scatter_algorithm_tree_fanout",
                                        "Fanout for n-tree used for reduce_scatter 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_reduce_scatter_tree_fanout);

    coll_tuned_reduce_scatter_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,
                                      "reduce_scatter_algorithm_chain_fanout",
                                      "Fanout for chains used for reduce_scatter 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_reduce_scatter_chain_fanout);

    return (MPI_SUCCESS);
}


int ompi_coll_tuned_reduce_scatter_intra_do_forced(void *sbuf, void* rbuf, 
                                                   int *rcounts,
                                                   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:reduce_scatter_intra_do_forced selected algorithm %d", 
                 data->user_forced[REDUCESCATTER].algorithm));

    switch (data->user_forced[REDUCESCATTER].algorithm) {
    case (0): return ompi_coll_tuned_reduce_scatter_intra_dec_fixed (sbuf, rbuf, rcounts, 
                                                                     dtype, op, comm, module);
    case (1): return ompi_coll_tuned_reduce_scatter_intra_nonoverlapping(sbuf, rbuf, rcounts,
                                                                         dtype, op, comm, module);
    case (2): return ompi_coll_tuned_reduce_scatter_intra_basic_recursivehalving(sbuf, rbuf, rcounts,
                                                                                 dtype, op, comm, module);
    case (3): return ompi_coll_tuned_reduce_scatter_intra_ring (sbuf, rbuf, rcounts,
                                                                dtype, op, comm, module);
    default:
        OPAL_OUTPUT((ompi_coll_tuned_stream,"coll:tuned:reduce_scatter_intra_do_forced attempt to select algorithm %d when only 0-%d is valid?",
                     data->user_forced[REDUCESCATTER].algorithm, ompi_coll_tuned_forced_max_algorithms[REDUCESCATTER]));
        return (MPI_ERR_ARG);
    } /* switch */
}


int ompi_coll_tuned_reduce_scatter_intra_do_this(void *sbuf, void* rbuf, 
                                                 int *rcounts,
                                                 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:reduce_scatter_intra_do_this selected algorithm %d topo faninout %d segsize %d",
                 algorithm, faninout, segsize));
   
    switch (algorithm) {
    case (0): return ompi_coll_tuned_reduce_scatter_intra_dec_fixed (sbuf, rbuf, rcounts, 
                                                                     dtype, op, comm, module);
    case (1): return ompi_coll_tuned_reduce_scatter_intra_nonoverlapping(sbuf, rbuf, rcounts,
                                                                         dtype, op, comm, module);
    case (2): return ompi_coll_tuned_reduce_scatter_intra_basic_recursivehalving(sbuf, rbuf, rcounts,
                                                                                 dtype, op, comm, module);
    case (3): return ompi_coll_tuned_reduce_scatter_intra_ring (sbuf, rbuf, rcounts,
                                                                dtype, op, comm, module);
    default:
        OPAL_OUTPUT((ompi_coll_tuned_stream,"coll:tuned:reduce_scatter_intra_do_this attempt to select algorithm %d when only 0-%d is valid?",
                     algorithm, ompi_coll_tuned_forced_max_algorithms[REDUCESCATTER]));
        return (MPI_ERR_ARG);
    } /* switch */
}