mpi under the hood

Question

I need to deliver a presentation on programming in MPI. I need to add a segment on how MPI works under the hood. For Example What happens when I call MPI_Init?

Do you know of any good source from where I can learn these details?

Answer 1

MPI is a specification, not a particular implementation. The observable behavior is given in the MPI spec. How it works under the hood depends on the particular implementation. If you'd like to take a look at an example implementation, you might be interested in looking at MPICH2 and browsing their source code.

Answer 2

Complement your study of the source code of an implementation of MPI with consideration of how you would implement MPI_Init on your platform of choice. MPI sits on top of already available O/S functionality. I don't mean to suggest that you can figure out how a particular version of MPI is implemented by this approach, but to suggest that you can learn better what is going on under the hood by tackling the problem from another angle.

Answer 3

The MPI Spec contains the description of the knobs, sliders, and displays that are on the outside of the "black box" of each API.

The interior details of the black boxes will be implementation dependent...and will also depend on the interconnect (e.g. TCP, IBV, DAPL, etc), the OS (e.g. is the implementation using LSB, or native libraries, etc), and on many other factors to a lesser degree (e.g. message size thresholds will trigger different code paths, and so on). Using "strace" and "ltrace" on the a.out may provide some insight into the actual goings on inside the blackbox.

The best recommendation is to pick an open source implementation and examine the code to determine the internal details.