-/**
- * Alltoall pairwise
- *
- * this algorithm performs size steps (1<=s<=size) and
- * at each step s, a process p sends iand receive to.from a unique distinct remote process
- * size=5 : s=1: 4->0->1, 0->1->2, 1->2->3, ...
- * s=2: 3->0->2, 4->1->3, 0->2->4, 1->3->0 , 2->4->1
- * ....
- * Openmpi calls this routine when the message size sent to each rank is greater than 3000 bytes
- **/
-int smpi_coll_tuned_alltoall_pairwise(void *sendbuf, int sendcount,
- MPI_Datatype sendtype, void *recvbuf,
- int recvcount, MPI_Datatype recvtype,
- MPI_Comm comm)
-{
- int system_tag = 999;
- int rank, size, step, sendto, recvfrom, sendsize, recvsize;
-
- rank = smpi_comm_rank(comm);
- size = smpi_comm_size(comm);
- XBT_DEBUG("<%d> algorithm alltoall_pairwise() called.", rank);
- sendsize = smpi_datatype_size(sendtype);
- recvsize = smpi_datatype_size(recvtype);
- /* Perform pairwise exchange - starting from 1 so the local copy is last */
- for (step = 1; step < size + 1; step++) {
- /* who do we talk to in this step? */
- sendto = (rank + step) % size;
- recvfrom = (rank + size - step) % size;
- /* send and receive */
- smpi_mpi_sendrecv(&((char *) sendbuf)[sendto * sendsize * sendcount],
- sendcount, sendtype, sendto, system_tag,
- &((char *) recvbuf)[recvfrom * recvsize * recvcount],
- recvcount, recvtype, recvfrom, system_tag, comm,
- MPI_STATUS_IGNORE);
- }
- return MPI_SUCCESS;
-}
-
