How to make/configure an MPI project to run on multiple processes?

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I have a small piece of code that should run on multilple processes, which is :

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#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 output is :Hello world! I'm process 0 out of 1 processes.

although it should run on more than one process

We edited the run configurations arguments to "-np 2" so it would run on 2 processes but it always gives us 1 process no matter what the value is.

The used environment is:
Eclipse Juno on Ubuntu 12.04

Source of code: http://condor.cc.ku.edu/~grobe/docs/intro-MPI-C.shtml[^]

Posted 22-Mar-14 22:16pm

Afnan_

Updated 23-Mar-14 5:12am

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nv3 23-Mar-14 7:07am

How did you start your process? Please show us the exact command line with wich you ran the application.

Afnan_ 23-Mar-14 11:07am

I don't use commands to run the application, I just run it from the run button on Eclipse

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Richard MacCutchan · Answer 1 · 2014-03-23T02:09:00

Solution 1

As far as I can see you do not ever create any threads. The documentation for MPI_Init[^] does not mention creating threads.

Posted 23-Mar-14 2:09am

Richard MacCutchan

Comments

Afnan_ 23-Mar-14 11:09am

I am not using threads.

Richard MacCutchan 23-Mar-14 11:15am

So how do you expect to run multiple processes?

Afnan_ 23-Mar-14 11:21am

I was following this example: http://condor.cc.ku.edu/~grobe/docs/intro-MPI-C.shtml

Richard MacCutchan 23-Mar-14 12:12pm

Did you start the program with the mpirun command, as shown in the sample?

Afnan_ 23-Mar-14 12:16pm

No, I run my code using the run button on eclipse. Although I have a problem with configuring the run configuration for a MPI project.

Richard MacCutchan 23-Mar-14 12:35pm

Then it will not work, you must start it with the mpirun command.

Afnan_ 23-Mar-14 12:48pm

I did try this command and this is what I get:

main@C:~/Junoworkspace/testmillion$ mpicc test.c -o testmillion
test.c:33:17: warning: extra tokens at end of #include directive [enabled by default]
test.c:33:18: fatal error: mpi.h: No such file or directory
compilation terminated.

Although mpi.h is in the directory

Richard MacCutchan 23-Mar-14 14:03pm

That does not make sense, there are only 19 lines in your source, but that message is referring to line 33.

Try #include "mpi.h" : quotes rather than < and >.

Afnan_ 23-Mar-14 15:24pm

It is "mpi.h", i just mistyped it here.

Richard MacCutchan 24-Mar-14 4:49am

Why not use copy & paste, so we see exactly what you are doing?

nv3 · Answer 2 · 2014-03-23T23:32:00

Solution 2

You seem to be under the impression that the MPI_Init function will launch multiple processes for you. This is not the case. You have to run your program via the mpirun command, for example:

C++

$ mpirun -np 4 a.out

and mpirun will interpret the "-np 4" for you and launch the four processes. As you started your process manually (from the IDE) you will only have that single processes running.

Posted 23-Mar-14 23:32pm

nv3

Comments

Afnan_ 24-Mar-14 7:42am

I did try it and this is what I get an error:

main@C4C:~/Junoworkspace/testmillion$ mpirun -np 4 testmillion [proxy:0:0@C4C] HYDU_create_process (./utils/launch/launch.c:69): execvp error on file testmillion (No such file or directory) [proxy:0:0@C4C] HYDU_create_process (./utils/launch/launch.c:69): execvp error on file testmillion (No such file or directory) [proxy:0:0@C4C] HYDU_create_process (./utils/launch/launch.c:69): execvp error on file testmillion (No such file or directory) [proxy:0:0@C4C] HYDU_create_process (./utils/launch/launch.c:69): execvp error on file testmillion (No such file or directory)

nv3 24-Mar-14 7:59am

Read the error message: ... testmillion (No such file or directory)
I guess you have to specify the file extension of your testmillion program; the mpirun program tried to run your program testmillion, but could not find it.

Afnan_ 24-Mar-14 16:17pm

Thank you but I already read the error message and the file does exist and the extension is provided. If you have noticed I'm running the command within the directory itself "main@C4C:~/Junoworkspace/testmillion$ mpirun -np 4 testmillion", so it's pointing to the directory.

nv3 24-Mar-14 16:31pm

I would trust the error message in so far that execvp could not find your file testmillion, for whatever reason. If the file is in the directoy, I can't see any other reason than that you did not specify the correct file extension. And I did not see a file extension on the command line that you posted.

Afnan_ 25-Mar-14 2:08am

Okay, I'll look in to that.

Thank you for all your comments.