As George replied, yes, Open MPI does use sockets -- that's in the TCP BTL (BTL = byte transfer layer, or point-to-point messaging layer for many network types). Open MPI also uses shared memory for on-server communication. But Open MPI can also use lots of other network types, if they're available (e.g., InfiniBand, iWARP, usNIC, portals, ugini, ...etc.).
Note, too, that OMPI also uses sockets in the run-time system layer.
You might want to look at a few Open MPI developer videos we did at Greenplum a while ago. They talk about the general code base, and Brian's talk discusses in detail how the back-ends to MPI_SEND / MPI_RECV work, etc.
On Aug 23, 2013, at 1:54 AM, mahesh <mahsh.baheti_at_[hidden]> wrote:
> I know that its a huge code base. But, I am looking for specific answers like does OpenMPI use sockets? Can programs written without mpi libraries be run on
> clusters using orte(with some changes)? It would be really helpful if atleast these and related doubts can be solved.
> On Aug 22, 2013 (jsquyres) <jsquyres_at_[hidden]> wrote
>> Note that according to http://www.ohloh.net/p/openmpi, OMPI is over 3/4M lines of code. I doubt you will be able to get a thorough understanding of *all* of OMPI in a semester or two -- indeed, I doubt that any one Open MPI core developer has a thorough understanding of the whole code base (I know I don't!).
>> I don't say these things to discourage you; I actually just want to encourage you to set realistic expectations for what you'll be able to do.
>> Are there any particular areas that you'd like to focus on? MPI -- and the Open MPI implementation -- covers a *lot* of different subsystems and concepts.
>> On Aug 22, 2013, at 8:06 AM, mahesh <mahsh.baheti_at_[hidden]> wrote:
>>> I am an newbie to all MPI concepts and I would like to understand the MPI source code thoroughly for
>>> an academic project. So, what I need is an detailed explanation of how every framework and module
>>> works. It would be really helpful if wise people could point me to right direction.
>>> devel mailing list
>> Jeff Squyres
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