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From: Jeff Squyres \(jsquyres\) (jsquyres_at_[hidden])
Date: 2006-03-30 10:17:29

I think we should clarify here -- Ralph is talking about the run-time
layer in Open MPI (the Open Run-Time Environment -- ORTE), of which we
hide the majority of those details from MPI users. He is not talking
about the MPI semantics.
MPI applications will still need to use the MPI-2 API to effect MPI
"connected" semantics (spawn, publish/accept/connect, join).


        From: users-bounces_at_[hidden]
[mailto:users-bounces_at_[hidden]] On Behalf Of Ralph Castain
        Sent: Monday, March 27, 2006 10:34 AM
        To: Chris.Gottbrath_at_[hidden]; Open MPI Users
        Subject: Re: [OMPI users] How to establish communication between
two separate COM WORLD (fwd)
        At the moment, this is still in "design" - all I've done for now
is breadboard a connection that places them effectively in the same
comm_world. Each process in both jobs is given the complete comm info
for all the processes. Details of the MPI interface, however, remain to
be determined by my MPI colleagues.
        The mode isn't documented yet since it isn't available in any of
the current tarballs or releases. I'm working on the infrastructure to
allow multiple applications to collaborate across multiple clusters on a
separate development branch - this capability is buried in that work.
        I'm sure documentation will follow as soon as we get a little
further towards completing implementation.
        Chris Gottbrath wrote:

                Interesting. How would the two jobs be 'connected' in
                Would they share a single MPI_COMM_WORLD or would they
                be created with an intercommunicator to the other jobs
                If so, how would that intercommmunicator be obtained in
                Is this mode documented anywhere?
                Chris Gottbrath
                Partner Technologies Engineer Etnus, LLC
                Voice: 508-652-7700 x7735 Fax: 508-652-7787
                ---------- Forwarded message ----------
                Date: Mon, 27 Mar 2006 06:44:04 -0700
                From: Ralph Castain <rhc_at_[hidden]> <mailto:rhc_at_[hidden]>

                To: Open MPI Users <users_at_[hidden]>
                Subject: Re: [OMPI users] How to establish communication
between two separate
                    COM WORLD
                Actually, in a not-too-distant future release, there
will be an option to mpirun called "--connect"
                that will allow you to specify that this job is to be
connected to a specified earlier job. The
                run-time environment will then spawn the new job and
exchange all required communication information
                between the two jobs for you. You could therefore
accomplish your desired operation by:

                        nohup mpirun --np xx app1

                (system returns job number to you)

                        mpirun --np yy --connect job1 app2

                (system starts app2 and connects it to job1)
                Should be a little more transparent. No specific coding
for making the connection would be required
                in your application itself.
                Jean Latour wrote:
                      It seems to me there is only one way to create a
communication between
                      two MPI_COMM_WORLD : use MPI_Open_Port with a
                      IP + port address, and then MPI_comm_connect /
                      In order to ease the port number communication,
the use of MPI_publish-name
                      / MPI_lookup_name is also possible with the
constraint that the "publish"
                      must be done before the "lookup", and this
involves some synchronization
                      between the processes anyway.
                      Simple examples can be found in the handbook on
MPI : "Using MPI-2"
                      by William Gropp et al.
                      Best Regards,
                      Ali Eghlima wrote:
                            I have read MPI-2 documents as well as FAQ.
I am confused as the best way to
                            establish communication
                            between two MPI_COMM_WORLD which has been
created by two mpiexec calls on
                            the same node.
                            mpiexec -conf config1
                                 This start 20 processes on 7 nodes
                            mpiexec -conf config2
                                  This start 18 processes on 5 nodes
                            I do appreciate any comments or pointer to a
document or example.
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