Hi, I want to test my own Alltoall implementation. To do that, I would like to modify MPIR_Alltoall_intra in src/mpi/coll/alltoall.c. Before that, I have checked (using MPIU_DBG_MSG) that my compiled version take the "good way": MPI_Alltoall->MPIR_Alltoall_impl->MPIR_Alltoall->MPIR_Alltoall_intra->"the good case", but it doesn't take this way. Instead of, in MPIR_Alltoall_impl, it calls comm_ptr->collfns->Alltoall. So I have two questions: - Is it the good way to add/modify some alltoall implementations ? - How to execute the good alltoall implementation ? Best regards, -- Antoine Rougier