--- /dev/null
+/* Copyright (c) 2013-2014. The SimGrid Team.
+ * All rights reserved. */
+
+/* This program is free software; you can redistribute it and/or modify it
+ * under the terms of the license (GNU LGPL) which comes with this package. */
+
+#include "colls_private.h"
+/*****************************************************************************
+
+ * Function: alltoall_pair_light_barrier
+
+ * Return: int
+
+ * Inputs:
+ send_buff: send input buffer
+ send_count: number of elements to send
+ send_type: data type of elements being sent
+ recv_buff: receive output buffer
+ recv_count: number of elements to received
+ recv_type: data type of elements being received
+ comm: communicator
+
+ * Descrp: Function works in P - 1 steps. In step i, node j exchanges data
+ with node i ^ j. Light barriers are inserted between
+ communications in different phases.
+
+ * Auther: Ahmad Faraj
+
+ ****************************************************************************/
+int
+smpi_coll_tuned_alltoall_pair_light_barrier(void *send_buff, int send_count,
+ MPI_Datatype send_type,
+ void *recv_buff, int recv_count,
+ MPI_Datatype recv_type,
+ MPI_Comm comm)
+{
+ MPI_Aint send_chunk, recv_chunk;
+ MPI_Status s;
+ int i, src, dst, rank, num_procs, next_partner;
+ int tag = COLL_TAG_ALLTOALL; /*, failure = 0; */
+
+ char send_sync = 'a', recv_sync = 'b';
+ char *send_ptr = (char *) send_buff;
+ char *recv_ptr = (char *) recv_buff;
+
+ rank = smpi_comm_rank(comm);
+ num_procs = smpi_comm_size(comm);
+
+ if((num_procs&(num_procs-1)))
+ THROWF(arg_error,0, "alltoall pair algorithm can't be used with non power of two number of processes ! ");
+
+ send_chunk = smpi_datatype_get_extent(send_type);
+ recv_chunk = smpi_datatype_get_extent(recv_type);
+
+ send_chunk *= send_count;
+ recv_chunk *= recv_count;
+
+ smpi_mpi_sendrecv(send_ptr + rank * send_chunk, send_count, send_type, rank, tag,
+ recv_ptr + rank * recv_chunk, recv_count, recv_type, rank, tag,
+ comm, &s);
+
+ for (i = 1; i < num_procs; i++) {
+ src = dst = rank ^ i;
+
+ smpi_mpi_sendrecv(send_ptr + dst * send_chunk, send_count, send_type,
+ dst, tag, recv_ptr + src * recv_chunk, recv_count,
+ recv_type, src, tag, comm, &s);
+
+ if ((i + 1) < num_procs) {
+ next_partner = rank ^ (i + 1);
+ smpi_mpi_sendrecv(&send_sync, 1, MPI_CHAR, next_partner, tag,
+ &recv_sync, 1, MPI_CHAR, next_partner, tag, comm, &s);
+ }
+ }
+ return MPI_SUCCESS;
+}