MPI Unexpected output | 易学教程

问题

I was reading and practicing MPI programs from a tutorial. There I saw an example of finding a rank of a process. But the same example is giving different output on my machine(Ubuntu 10.04).. Here is the program

 #include <stdio.h>
 #include <mpi.h> 
main(int argc, char **argv)
{
  int ierr, num_procs, my_id;

  ierr = MPI_Init(&argc, &argv);

  /* find out MY process ID, and how many processes were started. */

  ierr = MPI_Comm_rank(MPI_COMM_WORLD, &my_id);
  ierr = MPI_Comm_size(MPI_COMM_WORLD, &num_procs);

  printf("Hello world! I'm process %i out of %i processes\n", 
     my_id, num_procs);

  ierr = MPI_Finalize();
}

The expected output according to the tutorial is

Expected Output :

Hello world! I'm process 0 out of 4 processes.
Hello world! I'm process 2 out of 4 processes.
Hello world! I'm process 1 out of 4 processes.
Hello world! I'm process 3 out of 4 processes.

Output which I am getting

Hello world! I'm process 0 out of 1 processes
Hello world! I'm process 0 out of 1 processes
Hello world! I'm process 0 out of 1 processes
Hello world! I'm process 0 out of 1 processes

My machine uses intel i3,Dell Inspiron and is having Ubuntu 10.04 OS.Help me resolving the problem.

回答1:

I have just compiled and run your program on my Ubuntu:

tom@tom-ThinkPad-T500:~/MPI_projects/Start/net2/net2/bin/Debug$ mpirun -n 6 ./output
Hello world! I'm process 3 out of 6 processes
Hello world! I'm process 4 out of 6 processes
Hello world! I'm process 0 out of 6 processes
Hello world! I'm process 2 out of 6 processes
Hello world! I'm process 1 out of 6 processes
Hello world! I'm process 5 out of 6 processes

Enter the folder with your executable file and run:

mpirun -np 2 ./output

mpirun -np 6 ./output

the flag -np modifies the number of called processes (http://linux.die.net/man/1/mpirun).

You can also run mpirun without any flags to display lots of useful info.

Another interesting command is mpirun -info, which will show print MPI build information.

This is the first part of my output:

tom@tom-ThinkPad-T500:~/MPI_projects/Start/net2/net2/bin/Debug$ mpirun -info
HYDRA build details:
Version:                                 1.4.1
Release Date:                            Wed Aug 24 14:40:04 CDT 2011

The last resort is to re-install or update your MPI using, for example, the following command : sudo apt-get install libcr-dev mpich2 mpich2-doc

来源：https://stackoverflow.com/questions/15095121/mpi-unexpected-output

标签

parallel-processing

mpi

ubuntu-10.04