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Subject: Re: [OMPI users] TCP sockets opened by OpenMPI
From: Jeff Squyres (jsquyres_at_[hidden])
Date: 2009-11-15 11:43:51

On Nov 15, 2009, at 6:07 AM, Charles Salvia wrote:

> With using TCP with OpenMPI 1.3.3, how many sockets does each
> process open per peer-process? Does each process open a single
> socket to connect to each peer-process, or does it use TWO sockets,
> one for sending, one for receiving?

There are multiple flavors of TCP communication potentially happening
in each Open MPI process.

We use TCP sockets for control signals between mpirun and the MPI
process, for example. In the OMPI 1.3 series, this is a local TCP
socket to the "orted" helper daemon process that OMPI launches in the

Additionally, if you're using TCP and shared memory for MPI
communications (i.e., the TCP BTL module), Open MPI will lazily open 1
TCP socket to each non-local peer process which which you exchange MPI

Jeff Squyres