Teaching distributed memory programming from mental models

Abstract

Distributed memory programming, typically through the MPI library, is the de facto standard for programming large scale parallelism, with up to millions of individual processes. Its dominant paradigm of Single Program Multiple Data (SPMD) programming is different from threaded and multicore parallelism, to an extent that students have a hard time switching models. In contrast to threaded programming, which allows for a view of the execution with central control and a central repository of data, SPMD programming has a symmetric model where all processes are active all the time, with none privileged, and where data is distributed.This model is counterintuitive to the novice parallel programmer, so care needs to be taken how to instill the proper ‘mental model’. Adoption of an incorrect mental model leads to broken or inefficient code.We identify problems with the currently common way of teaching MPI, and propose a structuring of MPI courses that is geared to explicit reinforcing the symmetric model. Additionally, we advocate starting from realistic scenarios, rather than writing artificial code just to exercise newly-learned routines.