Merge pull request #3451 from mkurnosov/reduce-allreduce-rebenseifner

coll: Add Rabenseifner's algorithm for Reduce and Allreduce

ompi/mca/coll/spacc/Makefile.am

@@ -0,0 +1,35 @@
+#
+# $COPYRIGHT$
+#
+# Additional copyrights may follow
+#
+# $HEADER$
+#
+
+sources = \
+        coll_spacc.h \
+        coll_spacc_component.c \
+        coll_spacc_module.c \
+        coll_spacc_allreduce.c \
+        coll_spacc_reduce.c
+
+# Make the output library in this directory, and name it either
+# mca_<type>_<name>.la (for DSO builds) or libmca_<type>_<name>.la
+# (for static builds).
+
+if MCA_BUILD_ompi_coll_spacc_DSO
+component_noinst =
+component_install = mca_coll_spacc.la
+else
+component_noinst = libmca_coll_spacc.la
+component_install =
+endif
+
+mcacomponentdir = $(ompilibdir)
+mcacomponent_LTLIBRARIES = $(component_install)
+mca_coll_spacc_la_SOURCES = $(sources)
+mca_coll_spacc_la_LDFLAGS = -module -avoid-version
+
+noinst_LTLIBRARIES = $(component_noinst)
+libmca_coll_spacc_la_SOURCES =$(sources)
+libmca_coll_spacc_la_LDFLAGS = -module -avoid-version

ompi/mca/coll/spacc/coll_spacc.h

@@ -0,0 +1,83 @@
+/*
+ * $COPYRIGHT$
+ *
+ * Additional copyrights may follow
+ *
+ * $HEADER$
+ */
+
+#ifndef MCA_COLL_SPACC_EXPORT_H
+#define MCA_COLL_SPACC_EXPORT_H
+
+#include "ompi_config.h"
+
+#include "mpi.h"
+#include "ompi/mca/coll/coll.h"
+
+BEGIN_C_DECLS
+
+/* Globally exported variables */
+extern int ompi_coll_spacc_stream;
+extern int ompi_coll_spacc_priority;
+
+/* API functions */
+
+int mca_coll_spacc_init_query(bool enable_progress_threads,
+                              bool enable_mpi_threads);
+mca_coll_base_module_t
+*mca_coll_spacc_comm_query(struct ompi_communicator_t *comm, int *priority);
+
+int mca_coll_spacc_module_enable(mca_coll_base_module_t *module,
+                                 struct ompi_communicator_t *comm);
+
+int mca_coll_spacc_allreduce_intra_redscat_allgather(
+    const 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 mca_coll_spacc_reduce_intra_redscat_gather(
+    const 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);
+
+/*
+ * coll API functions
+ */
+
+/* API functions */
+
+int ompi_coll_spacc_init_query(bool enable_progress_threads,
+                                bool enable_mpi_threads);
+
+mca_coll_base_module_t *
+ompi_coll_spacc_comm_query(struct ompi_communicator_t *comm, int *priority);
+
+struct mca_coll_spacc_component_t {
+    /* Base coll component */
+    mca_coll_base_component_2_0_0_t super;
+
+    /* MCA parameter: priority of this component */
+    int spacc_priority;
+
+    /* global stuff that I need the component to store */
+
+    /* MCA parameters first */
+};
+
+/*
+ * Convenience typedef
+ */
+typedef struct mca_coll_spacc_component_t mca_coll_spacc_component_t;
+
+/*
+ * Global component instance
+ */
+OMPI_MODULE_DECLSPEC extern mca_coll_spacc_component_t mca_coll_spacc_component;
+
+struct mca_coll_spacc_module_t {
+    mca_coll_base_module_t super;
+};
+typedef struct mca_coll_spacc_module_t mca_coll_spacc_module_t;
+OBJ_CLASS_DECLARATION(mca_coll_spacc_module_t);
+
+#endif  /* MCA_COLL_SPACC_EXPORT_H */

ompi/mca/coll/spacc/coll_spacc_allreduce.c

@@ -0,0 +1,354 @@
+/*
+ * $COPYRIGHT$
+ *
+ * Additional copyrights may follow
+ *
+ * $HEADER$
+ */
+
+#include "ompi_config.h"
+#include "coll_spacc.h"
+
+#include "mpi.h"
+#include "ompi/constants.h"
+#include "opal/util/bit_ops.h"
+#include "ompi/datatype/ompi_datatype.h"
+#include "ompi/communicator/communicator.h"
+#include "ompi/mca/coll/coll.h"
+#include "ompi/mca/coll/base/coll_base_functions.h"
+#include "ompi/mca/coll/base/coll_tags.h"
+#include "ompi/mca/coll/base/coll_base_util.h"
+#include "ompi/mca/pml/pml.h"
+#include "ompi/op/op.h"
+
+/*
+ * mca_coll_spacc_allreduce_intra_redscat_gather
+ *
+ * Function:  Allreduce using Rabenseifner's algorithm.
+ * Accepts:   Same arguments as MPI_Allreduce
+ * Returns:   MPI_SUCCESS or error code
+ *
+ * Description: an implementation of Rabenseifner's allreduce algorithm [1, 2].
+ *   [1] Rajeev Thakur, Rolf Rabenseifner and William Gropp.
+ *       Optimization of Collective Communication Operations in MPICH //
+ *       The Int. Journal of High Performance Computing Applications. Vol 19,
+ *       Issue 1, pp. 49--66.
+ *   [2] http://www.hlrs.de/mpi/myreduce.html.
+ * 
+ * This algorithm is a combination of a reduce-scatter implemented with
+ * recursive vector halving and recursive distance doubling, followed either
+ * by an allgather implemented with recursive doubling [1].
+ * 
+ * Step 1. If the number of processes is not a power of two, reduce it to
+ * the nearest lower power of two (p' = 2^{\floor{\log_2 p}})
+ * by removing r = p - p' extra processes as follows. In the first 2r processes
+ * (ranks 0 to 2r - 1), all the even ranks send the second half of the input
+ * vector to their right neighbor (rank + 1), and all the odd ranks send
+ * the first half of the input vector to their left neighbor (rank - 1).
+ * The even ranks compute the reduction on the first half of the vector and
+ * the odd ranks compute the reduction on the second half. The odd ranks then
+ * send the result to their left neighbors (the even ranks). As a result,
+ * the even ranks among the first 2r processes now contain the reduction with
+ * the input vector on their right neighbors (the odd ranks). These odd ranks
+ * do not participate in the rest of the algorithm, which leaves behind
+ * a power-of-two number of processes. The first r even-ranked processes and
+ * the last p - 2r processes are now renumbered from 0 to p' - 1.
+ *
+ * Step 2. The remaining processes now perform a reduce-scatter by using
+ * recursive vector halving and recursive distance doubling. The even-ranked
+ * processes send the second half of their buffer to rank + 1 and the odd-ranked
+ * processes send the first half of their buffer to rank - 1. All processes
+ * then compute the reduction between the local buffer and the received buffer.
+ * In the next log_2(p') - 1 steps, the buffers are recursively halved, and the
+ * distance is doubled. At the end, each of the p' processes has 1 / p' of the
+ * total reduction result.
+ *
+ * Step 3. An allgather is performed by using recursive vector doubling and
+ * distance halving. All exchanges are executed in reverse order relative
+ * to recursive doubling on previous step. If the number of processes is not
+ * a power of two, the total result vector must be sent to the r processes
+ * that were removed in the first step.
+ * 
+ * Limitations:
+ *   count >= 2^{\floor{\log_2 p}}
+ *   commutative operations only
+ *   intra-communicators only
+ *
+ * Memory requirements (per process):
+ *   count * typesize + 4 * log_2(p) * sizeof(int) = O(count)
+ */
+int mca_coll_spacc_allreduce_intra_redscat_allgather(
+    const 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 *rindex = NULL, *rcount = NULL, *sindex = NULL, *scount = NULL;
+
+    int comm_size = ompi_comm_size(comm);
+    int rank = ompi_comm_rank(comm);
+
+    OPAL_OUTPUT((ompi_coll_spacc_stream,
+                "coll:spacc:allreduce_intra_redscat_allgather: rank %d/%d",
+                rank, comm_size));
+
+    /* Find nearest power-of-two less than or equal to comm_size */
+    int nsteps = opal_hibit(comm_size, comm->c_cube_dim + 1);   /* ilog2(comm_size) */
+    int nprocs_pof2 = 1 << nsteps;                              /* flp2(comm_size) */
+
+    if (count < nprocs_pof2 || !ompi_op_is_commute(op)) {
+        OPAL_OUTPUT((ompi_coll_spacc_stream,
+                    "coll:spacc:allreduce_intra_redscat_allgather: rank %d/%d count %d switching to base allreduce",
+                    rank, comm_size, count));
+        return ompi_coll_base_allreduce_intra_basic_linear(sbuf, rbuf, count, dtype,
+                                                           op, comm, module);
+    }
+
+    int err = MPI_SUCCESS;
+
+    ptrdiff_t lb, extent, dsize, gap = 0;
+    ompi_datatype_get_extent(dtype, &lb, &extent);
+    dsize = opal_datatype_span(&dtype->super, count, &gap);
+
+    /* Temporary buffer for receiving messages */
+    char *tmp_buf = NULL;
+    char *tmp_buf_raw = (char *)malloc(dsize);
+    if (NULL == tmp_buf_raw)
+        return OMPI_ERR_OUT_OF_RESOURCE;
+    tmp_buf = tmp_buf_raw - gap;
+
+    if (sbuf != MPI_IN_PLACE) {
+        /* Copy sbuf to rbuf */
+        err = ompi_datatype_copy_content_same_ddt(dtype, count, (char *)rbuf,
+                                                  (char *)sbuf);
+    }
+
+    /*
+     * Step 1. Reduce the number of processes to the nearest lower power of two
+     * p' = 2^{\floor{\log_2 p}} by removing r = p - p' processes.
+     * 1. In the first 2r processes (ranks 0 to 2r - 1), all the even ranks send
+     *    the second half of the input vector to their right neighbor (rank + 1)
+     *    and all the odd ranks send the first half of the input vector to their
+     *    left neighbor (rank - 1).
+     * 2. All 2r processes compute the reduction on their half.
+     * 3. The odd ranks then send the result to their left neighbors
+     *    (the even ranks).
+     *
+     * The even ranks (0 to 2r - 1) now contain the reduction with the input
+     * vector on their right neighbors (the odd ranks). The first r even
+     * processes and the p - 2r last processes are renumbered from
+     * 0 to 2^{\floor{\log_2 p}} - 1.
+     */
+
+    int vrank, step, wsize;
+    int nprocs_rem = comm_size - nprocs_pof2;
+
+    if (rank < 2 * nprocs_rem) {
+        int count_lhalf = count / 2;
+        int count_rhalf = count - count_lhalf;
+
+        if (rank % 2 != 0) {
+            /*
+             * Odd process -- exchange with rank - 1
+             * Send the left half of the input vector to the left neighbor,
+             * Recv the right half of the input vector from the left neighbor
+             */
+            err = ompi_coll_base_sendrecv(rbuf, count_lhalf, dtype, rank - 1,
+                                          MCA_COLL_BASE_TAG_ALLREDUCE,
+                                          (char *)tmp_buf + (ptrdiff_t)count_lhalf * extent,
+                                          count_rhalf, dtype, rank - 1,
+                                          MCA_COLL_BASE_TAG_ALLREDUCE, comm,
+                                          MPI_STATUS_IGNORE, rank);
+            if (MPI_SUCCESS != err) { goto cleanup_and_return; }
+
+            /* Reduce on the right half of the buffers (result in rbuf) */
+            ompi_op_reduce(op, (char *)tmp_buf + (ptrdiff_t)count_lhalf * extent,
+                           (char *)rbuf + count_lhalf * extent, count_rhalf, dtype);
+
+            /* Send the right half to the left neighbor */
+            err = MCA_PML_CALL(send((char *)rbuf + (ptrdiff_t)count_lhalf * extent,
+                                    count_rhalf, dtype, rank - 1,
+                                    MCA_COLL_BASE_TAG_ALLREDUCE,
+                                    MCA_PML_BASE_SEND_STANDARD, comm));
+            if (MPI_SUCCESS != err) { goto cleanup_and_return; }
+
+            /* This process does not pariticipate in recursive doubling phase */
+            vrank = -1;
+
+        } else {
+            /*
+             * Even process -- exchange with rank + 1
+             * Send the right half of the input vector to the right neighbor,
+             * Recv the left half of the input vector from the right neighbor
+             */
+            err = ompi_coll_base_sendrecv((char *)rbuf + (ptrdiff_t)count_lhalf * extent,
+                                          count_rhalf, dtype, rank + 1,
+                                          MCA_COLL_BASE_TAG_ALLREDUCE,
+                                          tmp_buf, count_lhalf, dtype, rank + 1,
+                                          MCA_COLL_BASE_TAG_ALLREDUCE, comm,
+                                          MPI_STATUS_IGNORE, rank);
+            if (MPI_SUCCESS != err) { goto cleanup_and_return; }
+
+            /* Reduce on the right half of the buffers (result in rbuf) */
+            ompi_op_reduce(op, tmp_buf, rbuf, count_lhalf, dtype);
+
+            /* Recv the right half from the right neighbor */
+            err = MCA_PML_CALL(recv((char *)rbuf + (ptrdiff_t)count_lhalf * extent,
+                                    count_rhalf, dtype, rank + 1,
+                                    MCA_COLL_BASE_TAG_ALLREDUCE, comm,
+                                    MPI_STATUS_IGNORE));
+            if (MPI_SUCCESS != err) { goto cleanup_and_return; }
+
+            vrank = rank / 2;
+        }
+    } else { /* rank >= 2 * nprocs_rem */
+        vrank = rank - nprocs_rem;
+    }
+
+    /*
+     * Step 2. Reduce-scatter implemented with recursive vector halving and
+     * recursive distance doubling. We have p' = 2^{\floor{\log_2 p}}
+     * power-of-two number of processes with new ranks (vrank) and result in rbuf.
+     *
+     * The even-ranked processes send the right half of their buffer to rank + 1
+     * and the odd-ranked processes send the left half of their buffer to
+     * rank - 1. All processes then compute the reduction between the local
+     * buffer and the received buffer. In the next \log_2(p') - 1 steps, the
+     * buffers are recursively halved, and the distance is doubled. At the end,
+     * each of the p' processes has 1 / p' of the total reduction result.
+     */
+    rindex = malloc(sizeof(*rindex) * nsteps);
+    sindex = malloc(sizeof(*sindex) * nsteps);
+    rcount = malloc(sizeof(*rcount) * nsteps);
+    scount = malloc(sizeof(*scount) * nsteps);
+    if (NULL == rindex || NULL == sindex || NULL == rcount || NULL == scount) {
+        err = OMPI_ERR_OUT_OF_RESOURCE;
+        goto cleanup_and_return;
+    }
+
+    if (vrank != -1) {
+        step = 0;
+        wsize = count;
+        sindex[0] = rindex[0] = 0;
+
+        for (int mask = 1; mask < nprocs_pof2; mask <<= 1) {
+            /*
+             * On each iteration: rindex[step] = sindex[step] -- begining of the
+             * current window. Length of the current window is storded in wsize.
+             */
+            int vdest = vrank ^ mask;
+            /* Translate vdest virtual rank to real rank */
+            int dest = (vdest < nprocs_rem) ? vdest * 2 : vdest + nprocs_rem;
+
+            if (rank < dest) {
+                /*
+                 * Recv into the left half of the current window, send the right
+                 * half of the window to the peer (perform reduce on the left
+                 * half of the current window)
+                 */
+                rcount[step] = wsize / 2;
+                scount[step] = wsize - rcount[step];
+                sindex[step] = rindex[step] + rcount[step];
+            } else {
+                /*
+                 * Recv into the right half of the current window, send the left
+                 * half of the window to the peer (perform reduce on the right
+                 * half of the current window)
+                 */
+                scount[step] = wsize / 2;
+                rcount[step] = wsize - scount[step];
+                rindex[step] = sindex[step] + scount[step];
+            }
+
+            /* Send part of data from the rbuf, recv into the tmp_buf */
+            err = ompi_coll_base_sendrecv((char *)rbuf + (ptrdiff_t)sindex[step] * extent,
+                                          scount[step], dtype, dest,
+                                          MCA_COLL_BASE_TAG_ALLREDUCE,
+                                          (char *)tmp_buf + (ptrdiff_t)rindex[step] * extent,
+                                          rcount[step], dtype, dest,
+                                          MCA_COLL_BASE_TAG_ALLREDUCE, comm,
+                                          MPI_STATUS_IGNORE, rank);
+            if (MPI_SUCCESS != err) { goto cleanup_and_return; }
+
+            /* Local reduce: rbuf[] = tmp_buf[] <op> rbuf[] */
+            ompi_op_reduce(op, (char *)tmp_buf + (ptrdiff_t)rindex[step] * extent,
+                           (char *)rbuf + (ptrdiff_t)rindex[step] * extent,
+                           rcount[step], dtype);
+
+            /* Move the current window to the received message */
+            rindex[step + 1] = rindex[step];
+            sindex[step + 1] = rindex[step];
+            wsize = rcount[step];
+            step++;
+        }
+    }
+    /*
+     * Assertion: each process has 1 / p' of the total reduction result:
+     * rcount[nsteps - 1] elements in the rbuf[rindex[nsteps - 1], ...].
+     */
+
+    /*
+     * Step 3. Allgather by the recursive doubling algorithm.
+     * Each process has 1 / p' of the total reduction result:
+     * rcount[nsteps - 1] elements in the rbuf[rindex[nsteps - 1], ...].
+     * All exchanges are executed in reverse order relative
+     * to recursive doubling (previous step).
+     */
+
+    if (vrank != -1) {
+        step = nsteps - 1; /* step = ilog2(p') - 1 */
+
+        for (int mask = nprocs_pof2 >> 1; mask > 0; mask >>= 1) {
+            int vdest = vrank ^ mask;
+            /* Translate vdest virtual rank to real rank */
+            int dest = (vdest < nprocs_rem) ? vdest * 2 : vdest + nprocs_rem;
+
+            /*
+             * Send rcount[step] elements from rbuf[rindex[step]...]
+             * Recv scount[step] elements to rbuf[sindex[step]...]
+             */
+            err = ompi_coll_base_sendrecv((char *)rbuf + (ptrdiff_t)rindex[step] * extent,
+                                          rcount[step], dtype, dest,
+                                          MCA_COLL_BASE_TAG_ALLREDUCE,
+                                          (char *)rbuf + (ptrdiff_t)sindex[step] * extent,
+                                          scount[step], dtype, dest,
+                                          MCA_COLL_BASE_TAG_ALLREDUCE, comm,
+                                          MPI_STATUS_IGNORE, rank);
+            if (MPI_SUCCESS != err) { goto cleanup_and_return; }
+            step--;
+        }
+    }
+
+    /*
+     * Step 4. Send total result to excluded odd ranks.
+     */
+    if (rank < 2 * nprocs_rem) {
+        if (rank % 2 != 0) {
+            /* Odd process -- recv result from rank - 1 */
+            err = MCA_PML_CALL(recv(rbuf, count, dtype, rank - 1,
+                                    MCA_COLL_BASE_TAG_ALLREDUCE, comm,
+                                    MPI_STATUS_IGNORE));
+            if (OMPI_SUCCESS != err) { goto cleanup_and_return; }
+
+        } else {
+            /* Even process -- send result to rank + 1 */
+            err = MCA_PML_CALL(send(rbuf, count, dtype, rank + 1,
+                                    MCA_COLL_BASE_TAG_ALLREDUCE,
+                                    MCA_PML_BASE_SEND_STANDARD, comm));
+            if (MPI_SUCCESS != err) { goto cleanup_and_return; }
+        }
+    }
+
+  cleanup_and_return:
+    if (NULL != tmp_buf_raw)
+        free(tmp_buf_raw);
+    if (NULL != rindex)
+        free(rindex);
+    if (NULL != sindex)
+        free(sindex);
+    if (NULL != rcount)
+        free(rcount);
+    if (NULL != scount)
+        free(scount);
+
+    return err;
+}

ompi/mca/coll/spacc/coll_spacc_component.c

@@ -0,0 +1,104 @@
+/*
+ * $COPYRIGHT$
+ *
+ * Additional copyrights may follow
+ *
+ * $HEADER$
+ */
+
+#include "ompi_config.h"
+
+#include "mpi.h"
+#include "ompi/mca/coll/coll.h"
+#include "coll_spacc.h"
+
+/*
+ * Public string showing the coll ompi_spacc component version number
+ */
+const char *ompi_coll_spacc_component_version_string =
+    "Open MPI SPACC collective MCA component version " OMPI_VERSION;
+
+/*
+ * Global variable
+ */
+int ompi_coll_spacc_priority = 5;
+int ompi_coll_spacc_stream = -1;
+
+/*
+ * Local function
+ */
+static int spacc_register(void);
+static int spacc_open(void);
+static int spacc_close(void);
+
+/*
+ * Instantiate the public struct with all of our public information
+ * and pointers to our public functions in it
+ */
+mca_coll_spacc_component_t mca_coll_spacc_component = {
+    /* First, fill in the super */
+    {
+        /* First, the mca_component_t struct containing meta information
+           about the component itself */
+        .collm_version = {
+            MCA_COLL_BASE_VERSION_2_0_0,
+
+            /* Component name and version */
+            .mca_component_name = "spacc",
+            MCA_BASE_MAKE_VERSION(component, OMPI_MAJOR_VERSION, OMPI_MINOR_VERSION,
+                                  OMPI_RELEASE_VERSION),
+
+            /* Component open and close functions */
+            .mca_open_component = spacc_open,
+            .mca_close_component = spacc_close,
+            .mca_register_component_params = spacc_register,
+        },
+        .collm_data = {
+            /* The component is checkpoint ready */
+            MCA_BASE_METADATA_PARAM_CHECKPOINT
+        },
+
+        /* Initialization / querying functions */
+        .collm_init_query = ompi_coll_spacc_init_query,
+        .collm_comm_query = ompi_coll_spacc_comm_query,
+    }
+};
+
+static int spacc_register(void)
+{
+    /* Use a low priority, but allow other components to be lower */
+    ompi_coll_spacc_priority = 5;
+    (void)mca_base_component_var_register(&mca_coll_spacc_component.super.collm_version,
+                                          "priority", "Priority of the spacc coll component",
+                                          MCA_BASE_VAR_TYPE_INT, NULL, 0, 0,
+                                          OPAL_INFO_LVL_6,
+                                          MCA_BASE_VAR_SCOPE_READONLY,
+                                          &ompi_coll_spacc_priority);
+    return OMPI_SUCCESS;
+}
+
+static int spacc_open(void)
+{
+#if OPAL_ENABLE_DEBUG
+    {
+        int param;
+
+        param = mca_base_var_find("ompi", "coll", "base", "verbose");
+        if (param >= 0) {
+            const int *verbose = NULL;
+            mca_base_var_get_value(param, &verbose, NULL, NULL);
+            if (verbose && verbose[0] > 0) {
+                ompi_coll_spacc_stream = opal_output_open(NULL);
+            }
+        }
+    }
+#endif  /* OPAL_ENABLE_DEBUG */
+    OPAL_OUTPUT((ompi_coll_spacc_stream, "coll:spacc:component_open: done"));
+    return OMPI_SUCCESS;
+}
+
+static int spacc_close(void)
+{
+    OPAL_OUTPUT((ompi_coll_spacc_stream, "coll:spacc:component_close: done"));
+    return OMPI_SUCCESS;
+}

ompi/mca/coll/spacc/coll_spacc_module.c

@@ -0,0 +1,97 @@
+/*
+ * $COPYRIGHT$
+ *
+ * Additional copyrights may follow
+ *
+ * $HEADER$
+ */
+
+#include "ompi_config.h"
+
+#include "mpi.h"
+#include "ompi/communicator/communicator.h"
+#include "ompi/mca/coll/base/base.h"
+#include "ompi/mca/coll/coll.h"
+#include "coll_spacc.h"
+
+static int spacc_module_enable(mca_coll_base_module_t *module,
+                               struct ompi_communicator_t *comm);
+/*
+ * Initial query function that is invoked during MPI_INIT, allowing
+ * this component to disqualify itself if it doesn't support the
+ * required level of thread support.
+ */
+int ompi_coll_spacc_init_query(bool enable_progress_threads,
+                               bool enable_mpi_threads)
+{
+    return OMPI_SUCCESS;
+}
+
+/*
+ * Invoked when there's a new communicator that has been created.
+ * Look at the communicator and decide which set of functions and
+ * priority we want to return.
+ */
+mca_coll_base_module_t *ompi_coll_spacc_comm_query(
+    struct ompi_communicator_t *comm, int *priority)
+{
+    mca_coll_spacc_module_t *spacc_module;
+
+    OPAL_OUTPUT((ompi_coll_spacc_stream, "coll:spacc:module_spacc query called"));
+
+    if (OMPI_COMM_IS_INTER(comm)) {
+        *priority = 0;
+        return NULL;
+    }
+
+    if (OMPI_COMM_IS_INTRA(comm) && ompi_comm_size(comm) < 2) {
+        *priority = 0;
+        return NULL;
+    }
+
+    spacc_module = OBJ_NEW(mca_coll_spacc_module_t);
+    if (NULL == spacc_module)
+        return NULL;
+
+    *priority = ompi_coll_spacc_priority;
+
+    spacc_module->super.coll_module_enable = spacc_module_enable;
+    spacc_module->super.ft_event = NULL;
+    spacc_module->super.coll_allgather  = NULL;
+    spacc_module->super.coll_allgatherv = NULL;
+    spacc_module->super.coll_allreduce  = mca_coll_spacc_allreduce_intra_redscat_allgather;
+    spacc_module->super.coll_alltoall   = NULL;
+    spacc_module->super.coll_alltoallv  = NULL;
+    spacc_module->super.coll_alltoallw  = NULL;
+    spacc_module->super.coll_barrier    = NULL;
+    spacc_module->super.coll_bcast      = NULL;
+    spacc_module->super.coll_exscan     = NULL;
+    spacc_module->super.coll_gather     = NULL;
+    spacc_module->super.coll_gatherv    = NULL;
+    spacc_module->super.coll_reduce     = mca_coll_spacc_reduce_intra_redscat_gather;
+    spacc_module->super.coll_reduce_scatter_block = NULL;
+    spacc_module->super.coll_reduce_scatter = NULL;
+    spacc_module->super.coll_scan       = NULL;
+    spacc_module->super.coll_scatter    = NULL;
+    spacc_module->super.coll_scatterv   = NULL;
+
+    return &(spacc_module->super);
+}
+
+/*
+ * Init module on the communicator
+ */
+static int spacc_module_enable(mca_coll_base_module_t *module,
+                               struct ompi_communicator_t *comm)
+{
+    OPAL_OUTPUT((ompi_coll_spacc_stream, "coll:spacc:module_enable called."));
+    return OMPI_SUCCESS;
+}
+
+static void mca_coll_spacc_module_construct(mca_coll_spacc_module_t *module)
+{
+    /* mca_coll_spacc_module_t *spacc_module = (mca_coll_spacc_module_t*)module; */
+}
+
+OBJ_CLASS_INSTANCE(mca_coll_spacc_module_t, mca_coll_base_module_t,
+                   mca_coll_spacc_module_construct, NULL);

ompi/mca/coll/spacc/coll_spacc_reduce.c

@@ -0,0 +1,413 @@
+/*
+ * $COPYRIGHT$
+ *
+ * Additional copyrights may follow
+ *
+ * $HEADER$
+ */
+
+#include "ompi_config.h"
+#include "coll_spacc.h"
+
+#include "mpi.h"
+#include "ompi/constants.h"
+#include "opal/util/bit_ops.h"
+#include "ompi/datatype/ompi_datatype.h"
+#include "ompi/communicator/communicator.h"
+#include "ompi/mca/coll/coll.h"
+#include "ompi/mca/coll/base/coll_base_functions.h"
+#include "ompi/mca/coll/base/coll_tags.h"
+#include "ompi/mca/coll/base/coll_base_util.h"
+#include "ompi/mca/pml/pml.h"
+#include "ompi/op/op.h"
+
+/*
+ * mca_coll_spacc_reduce_intra_redscat_gather
+ *
+ * Function:  Reduce using Rabenseifner's algorithm.
+ * Accepts:   Same arguments as MPI_Reduce
+ * Returns:   MPI_SUCCESS or error code
+ *
+ * Description: an implementation of Rabenseifner's reduce algorithm [1, 2].
+ *   [1] Rajeev Thakur, Rolf Rabenseifner and William Gropp.
+ *       Optimization of Collective Communication Operations in MPICH //
+ *       The Int. Journal of High Performance Computing Applications. Vol 19,
+ *       Issue 1, pp. 49--66.
+ *   [2] http://www.hlrs.de/mpi/myreduce.html.
+ *
+ * This algorithm is a combination of a reduce-scatter implemented with
+ * recursive vector halving and recursive distance doubling, followed either
+ * by a binomial tree gather [1].
+ * 
+ * Step 1. If the number of processes is not a power of two, reduce it to
+ * the nearest lower power of two (p' = 2^{\floor{\log_2 p}})
+ * by removing r = p - p' extra processes as follows. In the first 2r processes
+ * (ranks 0 to 2r - 1), all the even ranks send the second half of the input
+ * vector to their right neighbor (rank + 1), and all the odd ranks send
+ * the first half of the input vector to their left neighbor (rank - 1).
+ * The even ranks compute the reduction on the first half of the vector and
+ * the odd ranks compute the reduction on the second half. The odd ranks then
+ * send the result to their left neighbors (the even ranks). As a result,
+ * the even ranks among the first 2r processes now contain the reduction with
+ * the input vector on their right neighbors (the odd ranks). These odd ranks
+ * do not participate in the rest of the algorithm, which leaves behind
+ * a power-of-two number of processes. The first r even-ranked processes and
+ * the last p - 2r processes are now renumbered from 0 to p' - 1.
+ *
+ * Step 2. The remaining processes now perform a reduce-scatter by using
+ * recursive vector halving and recursive distance doubling. The even-ranked
+ * processes send the second half of their buffer to rank + 1 and the odd-ranked
+ * processes send the first half of their buffer to rank - 1. All processes
+ * then compute the reduction between the local buffer and the received buffer.
+ * In the next log_2(p') - 1 steps, the buffers are recursively halved, and the
+ * distance is doubled. At the end, each of the p' processes has 1 / p' of the
+ * total reduction result.
+ *
+ * Step 3. A binomial tree gather is performed by using recursive vector
+ * doubling and distance halving. In the non-power-of-two case, if the root
+ * happens to be one of those odd-ranked processes that would normally
+ * be removed in the first step, then the role of this process and process 0
+ * are interchanged.
+ * 
+ * Limitations:
+ *   count >= 2^{\floor{\log_2 p}}
+ *   commutative operations only
+ *   intra-communicators only
+ *
+ * Memory requirements (per process):
+ *   rank != root: 2 * count * typesize + 4 * log_2(p) * sizeof(int) = O(count)
+ *   rank == root: count * typesize + 4 * log_2(p) * sizeof(int) = O(count)
+ *
+ * Recommendations: root = 0, otherwise it is required additional steps
+ *                  in the root process.
+ */
+int mca_coll_spacc_reduce_intra_redscat_gather(
+    const 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 comm_size = ompi_comm_size(comm);
+    int rank = ompi_comm_rank(comm);
+
+    OPAL_OUTPUT((ompi_coll_spacc_stream,
+                "coll:spacc:reduce_intra_redscat_gather: rank %d/%d, root %d",
+                rank, comm_size, root));
+
+    /* Find nearest power-of-two less than or equal to comm_size */
+    int nsteps = opal_hibit(comm_size, comm->c_cube_dim + 1);   /* ilog2(comm_size) */
+    int nprocs_pof2 = 1 << nsteps;                              /* flp2(comm_size) */
+
+    if (count < nprocs_pof2 || !ompi_op_is_commute(op)) {
+        OPAL_OUTPUT((ompi_coll_spacc_stream,
+                    "coll:spacc:reduce_intra_redscat_gather: rank %d/%d count %d switching to base reduce",
+                    rank, comm_size, count));
+        return ompi_coll_base_reduce_intra_basic_linear(sbuf, rbuf, count, dtype,
+                                                        op, root, comm, module);
+    }
+
+    int err = MPI_SUCCESS;
+    int *rindex = NULL, *rcount = NULL, *sindex = NULL, *scount = NULL;
+
+    ptrdiff_t lb, extent, dsize, gap;
+    ompi_datatype_get_extent(dtype, &lb, &extent);
+    dsize = opal_datatype_span(&dtype->super, count, &gap);
+
+    /* Temporary buffer for receiving messages */
+    char *tmp_buf = NULL;
+    char *tmp_buf_raw = (char *)malloc(dsize);
+    if (NULL == tmp_buf_raw)
+        return OMPI_ERR_OUT_OF_RESOURCE;
+    tmp_buf = tmp_buf_raw - gap;
+
+    char *rbuf_raw = NULL;
+    if (rank != root) {
+        rbuf_raw = (char *)malloc(dsize);
+        if (NULL == rbuf_raw) {
+            err = OMPI_ERR_OUT_OF_RESOURCE;
+            goto cleanup_and_return;
+        }
+        rbuf = rbuf_raw - gap;
+    }
+
+    if ((rank != root) || (sbuf != MPI_IN_PLACE)) {
+        /* Copy sbuf to rbuf */
+        err = ompi_datatype_copy_content_same_ddt(dtype, count, (char *)rbuf,
+                                                  (char *)sbuf);
+    }
+
+    /*
+     * Step 1. Reduce the number of processes to the nearest lower power of two
+     * p' = 2^{\floor{\log_2 p}} by removing r = p - p' processes.
+     * 1. In the first 2r processes (ranks 0 to 2r - 1), all the even ranks send
+     *    the second half of the input vector to their right neighbor (rank + 1)
+     *    and all the odd ranks send the first half of the input vector to their
+     *    left neighbor (rank - 1).
+     * 2. All 2r processes compute the reduction on their half.
+     * 3. The odd ranks then send the result to their left neighbors
+     *    (the even ranks).
+     *
+     * The even ranks (0 to 2r - 1) now contain the reduction with the input
+     * vector on their right neighbors (the odd ranks). The first r even
+     * processes and the p - 2r last processes are renumbered from
+     * 0 to 2^{\floor{\log_2 p}} - 1. These odd ranks do not participate in the
+     * rest of the algorithm.
+     */
+
+    int vrank, step, wsize;
+    int nprocs_rem = comm_size - nprocs_pof2;
+
+    if (rank < 2 * nprocs_rem) {
+        int count_lhalf = count / 2;
+        int count_rhalf = count - count_lhalf;
+
+        if (rank % 2 != 0) {
+            /*
+             * Odd process -- exchange with rank - 1
+             * Send the left half of the input vector to the left neighbor,
+             * Recv the right half of the input vector from the left neighbor
+             */
+            err = ompi_coll_base_sendrecv(rbuf, count_lhalf, dtype, rank - 1,
+                                          MCA_COLL_BASE_TAG_REDUCE,
+                                          (char *)tmp_buf + (ptrdiff_t)count_lhalf * extent,
+                                          count_rhalf, dtype, rank - 1,
+                                          MCA_COLL_BASE_TAG_REDUCE, comm,
+                                          MPI_STATUS_IGNORE, rank);
+            if (MPI_SUCCESS != err) { goto cleanup_and_return; }
+
+            /* Reduce on the right half of the buffers (result in rbuf) */
+            ompi_op_reduce(op, (char *)tmp_buf + (ptrdiff_t)count_lhalf * extent,
+                           (char *)rbuf + count_lhalf * extent, count_rhalf, dtype);
+
+            /* Send the right half to the left neighbor */
+            err = MCA_PML_CALL(send((char *)rbuf + (ptrdiff_t)count_lhalf * extent,
+                                    count_rhalf, dtype, rank - 1,
+                                    MCA_COLL_BASE_TAG_REDUCE,
+                                    MCA_PML_BASE_SEND_STANDARD, comm));
+            if (MPI_SUCCESS != err) { goto cleanup_and_return; }
+
+            /* This process does not pariticipate in recursive doubling phase */
+            vrank = -1;
+
+        } else {
+            /*
+             * Even process -- exchange with rank + 1
+             * Send the right half of the input vector to the right neighbor,
+             * Recv the left half of the input vector from the right neighbor
+             */
+            err = ompi_coll_base_sendrecv((char *)rbuf + (ptrdiff_t)count_lhalf * extent,
+                                          count_rhalf, dtype, rank + 1,
+                                          MCA_COLL_BASE_TAG_REDUCE,
+                                          tmp_buf, count_lhalf, dtype, rank + 1,
+                                          MCA_COLL_BASE_TAG_REDUCE, comm,
+                                          MPI_STATUS_IGNORE, rank);
+            if (MPI_SUCCESS != err) { goto cleanup_and_return; }
+
+            /* Reduce on the right half of the buffers (result in rbuf) */
+            ompi_op_reduce(op, tmp_buf, rbuf, count_lhalf, dtype);
+
+            /* Recv the right half from the right neighbor */
+            err = MCA_PML_CALL(recv((char *)rbuf + (ptrdiff_t)count_lhalf * extent,
+                                    count_rhalf, dtype, rank + 1,
+                                    MCA_COLL_BASE_TAG_REDUCE, comm,
+                                    MPI_STATUS_IGNORE));
+            if (MPI_SUCCESS != err) { goto cleanup_and_return; }
+
+            vrank = rank / 2;
+        }
+    } else { /* rank >= 2 * nprocs_rem */
+        vrank = rank - nprocs_rem;
+    }
+
+    /*
+     * Step 2. Reduce-scatter implemented with recursive vector halving and
+     * recursive distance doubling. We have p' = 2^{\floor{\log_2 p}}
+     * power-of-two number of processes with new ranks (vrank) and result in rbuf.
+     *
+     * The even-ranked processes send the right half of their buffer to rank + 1
+     * and the odd-ranked processes send the left half of their buffer to
+     * rank - 1. All processes then compute the reduction between the local
+     * buffer and the received buffer. In the next \log_2(p') - 1 steps, the
+     * buffers are recursively halved, and the distance is doubled. At the end,
+     * each of the p' processes has 1 / p' of the total reduction result.
+     */
+
+    rindex = malloc(sizeof(*rindex) * nsteps);    /* O(\log_2(p)) */
+    sindex = malloc(sizeof(*sindex) * nsteps);
+    rcount = malloc(sizeof(*rcount) * nsteps);
+    scount = malloc(sizeof(*scount) * nsteps);
+    if (NULL == rindex || NULL == sindex || NULL == rcount || NULL == scount) {
+        err = OMPI_ERR_OUT_OF_RESOURCE;
+        goto cleanup_and_return;
+    }
+
+    if (vrank != -1) {
+        step = 0;
+        wsize = count;
+        sindex[0] = rindex[0] = 0;
+
+        for (int mask = 1; mask < nprocs_pof2; mask <<= 1) {
+            /*
+             * On each iteration: rindex[step] = sindex[step] -- begining of the
+             * current window. Length of the current window is storded in wsize.
+             */
+            int vdest = vrank ^ mask;
+            /* Translate vdest virtual rank to real rank */
+            int dest = (vdest < nprocs_rem) ? vdest * 2 : vdest + nprocs_rem;
+
+            if (rank < dest) {
+                /*
+                 * Recv into the left half of the current window, send the right
+                 * half of the window to the peer (perform reduce on the left
+                 * half of the current window)
+                 */
+                rcount[step] = wsize / 2;
+                scount[step] = wsize - rcount[step];
+                sindex[step] = rindex[step] + rcount[step];
+            } else {
+                /*
+                 * Recv into the right half of the current window, send the left
+                 * half of the window to the peer (perform reduce on the right
+                 * half of the current window)
+                 */
+                scount[step] = wsize / 2;
+                rcount[step] = wsize - scount[step];
+                rindex[step] = sindex[step] + scount[step];
+            }
+
+            /* Send part of data from the rbuf, recv into the tmp_buf */
+            err = ompi_coll_base_sendrecv((char *)rbuf + (ptrdiff_t)sindex[step] * extent,
+                                          scount[step], dtype, dest,
+                                          MCA_COLL_BASE_TAG_REDUCE,
+                                          (char *)tmp_buf + (ptrdiff_t)rindex[step] * extent,
+                                          rcount[step], dtype, dest,
+                                          MCA_COLL_BASE_TAG_REDUCE, comm,
+                                          MPI_STATUS_IGNORE, rank);
+            if (MPI_SUCCESS != err) { goto cleanup_and_return; }
+
+            /* Local reduce: rbuf[] = tmp_buf[] <op> rbuf[] */
+            ompi_op_reduce(op, (char *)tmp_buf + (ptrdiff_t)rindex[step] * extent,
+                           (char *)rbuf + (ptrdiff_t)rindex[step] * extent,
+                           rcount[step], dtype);
+
+            /* Move the current window to the received message */
+            rindex[step + 1] = rindex[step];
+            sindex[step + 1] = rindex[step];
+            wsize = rcount[step];
+            step++;
+        }
+    }
+    /*
+     * Assertion: each process has 1 / p' of the total reduction result:
+     * rcount[nsteps - 1] elements in the rbuf[rindex[nsteps - 1], ...].
+     */
+
+    /*
+     * Setup the root process for gather operation.
+     * Case 1: root < 2r and root is odd -- root process was excluded on step 1
+     *         Recv data from process 0, vroot = 0, vrank = 0
+     * Case 2: root < 2r and root is even: vroot = root / 2
+     * Case 3: root >= 2r: vroot = root - r
+     */
+    int vroot = 0;
+    if (root < 2 * nprocs_rem) {
+        if (root % 2 != 0) {
+            vroot = 0;
+            if (rank == root) {
+                /*
+                 * Case 1: root < 2r and root is odd -- root process was
+                 * excluded on step 1 (newrank == -1).
+                 * Recv a data from the process 0.
+                 */
+                rindex[0] = 0;
+                step = 0, wsize = count;
+                for (int mask = 1; mask < nprocs_pof2; mask *= 2) {
+                    rcount[step] = wsize / 2;
+                    scount[step] = wsize - rcount[step];
+                    rindex[step] = 0;
+                    sindex[step] = rcount[step];
+                    step++;
+                    wsize /= 2;
+                }
+
+                err = MCA_PML_CALL(recv(rbuf, rcount[nsteps - 1], dtype, 0,
+                                        MCA_COLL_BASE_TAG_REDUCE, comm,
+                                        MPI_STATUS_IGNORE));
+                if (MPI_SUCCESS != err) { goto cleanup_and_return; }
+                vrank = 0;
+
+            } else if (vrank == 0) {
+                /* Send a data to the root */
+                err = MCA_PML_CALL(send(rbuf, rcount[nsteps - 1], dtype, root,
+                                        MCA_COLL_BASE_TAG_REDUCE,
+                                        MCA_PML_BASE_SEND_STANDARD, comm));
+                if (MPI_SUCCESS != err) { goto cleanup_and_return; }
+                vrank = -1;
+            }
+        } else {
+            /* Case 2: root < 2r and a root is even: vroot = root / 2 */
+            vroot = root / 2;
+        }
+    } else {
+        /* Case 3: root >= 2r: newroot = root - r */
+        vroot = root - nprocs_rem;
+    }
+
+    /*
+     * Step 3. Gather result at the vroot by the binomial tree algorithm.
+     * Each process has 1 / p' of the total reduction result:
+     * rcount[nsteps - 1] elements in the rbuf[rindex[nsteps - 1], ...].
+     * All exchanges are executed in reverse order relative
+     * to recursive doubling (previous step).
+     */
+
+    if (vrank != -1) {
+        int vdest_tree, vroot_tree;
+        step = nsteps - 1; /* step = ilog2(p') - 1 */
+
+        for (int mask = nprocs_pof2 >> 1; mask > 0; mask >>= 1) {
+            int vdest = vrank ^ mask;
+            /* Translate vdest virtual rank to real rank */
+            int dest = (vdest < nprocs_rem) ? vdest * 2 : vdest + nprocs_rem;
+            if ((vdest == 0) && (root < 2 * nprocs_rem) && (root % 2 != 0))
+                dest = root;
+
+            vdest_tree = vdest >> step;
+            vdest_tree <<= step;
+            vroot_tree = vroot >> step;
+            vroot_tree <<= step;
+            if (vdest_tree == vroot_tree) {
+                /* Send data from rbuf and exit */
+                err = MCA_PML_CALL(send((char *)rbuf + (ptrdiff_t)rindex[step] * extent,
+                                        rcount[step], dtype, dest,
+                                        MCA_COLL_BASE_TAG_REDUCE,
+                                        MCA_PML_BASE_SEND_STANDARD, comm));
+                if (MPI_SUCCESS != err) { goto cleanup_and_return; }
+                break;
+            } else {
+                /* Recv and continue */
+                err = MCA_PML_CALL(recv((char *)rbuf + (ptrdiff_t)sindex[step] * extent,
+                                        scount[step], dtype, dest,
+                                        MCA_COLL_BASE_TAG_REDUCE, comm,
+                                        MPI_STATUS_IGNORE));
+                if (MPI_SUCCESS != err) { goto cleanup_and_return; }
+            }
+            step--;
+        }
+    }
+
+  cleanup_and_return:
+    if (NULL != tmp_buf_raw)
+        free(tmp_buf_raw);
+    if (NULL != rbuf_raw)
+        free(rbuf_raw);
+    if (NULL != rindex)
+        free(rindex);
+    if (NULL != sindex)
+        free(sindex);
+    if (NULL != rcount)
+        free(rcount);
+    if (NULL != scount)
+        free(scount);
+
+    return err;
+}