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Subject: Re: [OMPI users] Scheduling dynamically spawned processes
From: Ralph Castain (rhc_at_[hidden])
Date: 2011-05-16 14:47:54


You need to use MPI_Comm_spawn_multiple. Despite the name, it results in a single communicator being created by a single launch - it just allows you to specify multiple applications to run.

In this case, we use the same app, but give each element a different "host" info key to get the behavior we want. Looks something like this:

    MPI_Comm child;
    char *cmds[3] = {"myapp", "myapp", "myapp"};
    MPI_Info info[3];
    int maxprocs[] = { 1, 3, 1 };

  MPI_Info_create(&info[0]);
  MPI_Info_set(info[0], "host", "m1");

  MPI_Info_create(&info[1]);
  MPI_Info_set(info[1], "host", "m2");

  MPI_Info_create(&info[2]);
  MPI_Info_set(info[2], "host", "m1");
  
        MPI_Comm_spawn_multiple(3, cmds, NULL, maxprocs,
                                info, 0, MPI_COMM_WORLD,
                                &child, MPI_ERRCODES_IGNORE);

I won't claim the above is correct - but it gives the gist of the idea.

On May 16, 2011, at 12:19 PM, Thatyene Louise Alves de Souza Ramos wrote:

> Ralph,
>
> I have the same issue and I've been searching how to do this, but I couldn't find.
>
> What exactly must be the string in the host info key to do what Rodrigo described?
>
> <<< Inside your master, you would create an MPI_Info key "host" that has a value
> <<< consisting of a string "host1,host2,host3" identifying the hosts you want
> <<< your slave to execute upon. Those hosts must have been included in
> <<< my_hostfile. Include that key in the MPI_Info array passed to your Spawn.
>
> I tried to do what you said above but ompi ignores the repetition of hosts. Using Rodrigo's example I did:
>
> host info key = "m1,m2,m2,m2,m3" and number of processes = 5 and the result was
>
> m1 -> 2
> m2 -> 2
> m3 -> 1
>
> and not
>
> m1 -> 1
> m2 -> 3
> m3 -> 1
>
> as I wanted.
>
> Thanks in advance.
>
> Thatyene Ramos
>
> On Fri, May 13, 2011 at 9:16 PM, Ralph Castain <rhc_at_[hidden]> wrote:
> I believe I answered that question. You can use the hostfile info key, or you can use the host info key - either one will do what you require.
>
> On May 13, 2011, at 4:11 PM, Rodrigo Silva Oliveira wrote:
>
>> Hi,
>>
>> I think I was not specific enough. I need to spawn the copies of a process in a unique mpi_spawn call. It is, I have to specify a list of machines and how many copies of the process will be spawned on each one. Is it possible?
>>
>> I would be something like that:
>>
>> machines #copies
>> m1 1
>> m2 3
>> m3 1
>>
>> After an unique call to spawn, I want the copies running in this fashion. I tried use a hostfile with the option slot, but I'm not sure if it is the best way.
>>
>> hostfile:
>>
>> m1 slots=1
>> m2 slots=3
>> m3 slots=1
>>
>> Thanks
>>
>> --
>> Rodrigo Silva Oliveira
>> M.Sc. Student - Computer Science
>> Universidade Federal de Minas Gerais
>> www.dcc.ufmg.br/~rsilva
>> _______________________________________________
>> users mailing list
>> users_at_[hidden]
>> http://www.open-mpi.org/mailman/listinfo.cgi/users
>
>
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