使用MPI_Send和Recv

Question

在我的应用程序中，所有处理器都必须发送和接收。为了计算单个链路的带宽，我使用MPI_Send和MPI_Recv。 （不要使用MPI广播） 我的问题是，我为同一链接获得不同的带宽。就像进程0向1发送一些数据时，带宽是不同的，反之亦然。必须相同。我在这里发布代码。请帮助我为什么同一链接获得不同的带宽？

                    if (comm_rank==source){
                        for (int i = 0; i < comm_size; i++) {
                            if (i != comm_rank) {

                                // Start time for A send
                                start_send = MPI_Wtime();
                                //Send data to other processors that don't own the sub-partition
                                rc =MPI_Send(tmp, elem_num, MPI_DOUBLE, i, 0, comm);
                                    rc= MPI_Recv(&recv_ack, 1, MPI_INT,i , 5, comm,&status);
                                // End time for A send;
                                end_send = MPI_Wtime();

                                //A send bandwidth calculation in Mb/sec
                                double  bandwidth_send= (elem_num * sizeof(double)*1.0e-6*8)/(end_send-start_send);
                                if (print_communication_times_to_file) {
                                    fprintf(dofp, "<--COMM-->: Rank[%d]: A communications(Send),(%d,%d)[%d] --> (%d,* [%d] = (%d elements)" " at index Local A(%d,%d), %f seconds, bandwidth= %8.2f\n", rank, blocki, blockj, rank,blocki,comm_world[i], elem_num, A_elem_i_local, A_elem_j_local,(end_send - start_send),bandwidth_send);
                                    fflush(dofp);
                                }
                            }
                        }
                    }else {
                        // Start time for A receive
                        start_recv = MPI_Wtime();
                        rc= MPI_Recv(tmp, elem_num, MPI_DOUBLE, source, 0, comm,&status);
                        // End time for A receive
                        end_recv = MPI_Wtime();
                        if (rc == MPI_SUCCESS) {
                            recv_ack=1;
                            rc =MPI_Send(&recv_ack, 1, MPI_INT, source, 5, comm);}