Object-Based Adaptive Load Balancing for MPI Programs∗

Parallel Computational Science and Engineering (CSE) applications often exhibit irregular structure and dynamic load patterns. Many such applications have been developed using procedural languages (e.g. Fortran) in message passing parallel programming paradigm (e.g. MPI) for distributed memory machines. Incorporating dynamic load balancing techniques at the application-level involves significant changes to the design and structure of applications. On the other hand, traditional run-time systems for MPI do not support dynamic load balancing. Object-based parallel programming languages, such as Charm++ support efficient dynamic load balancing using object migration for irregular and dynamic applications, as well as to deal with external factors that cause load imbalance. However, converting legacy MPI applications to such object-based paradigms is cumbersome. This paper describes an implementation of MPI, called Adaptive MPI (AMPI) that supports dynamic load balancing and multithreading for MPI applications. Our approach and implementation is based on the user-level migrating threads and load balancing capabilities provided by the Charm++ framework. Conversion from legacy codes to this platform is straightforward even for large legacy codes. We have converted the component codes ROCFLO and ROCSOLID of a Rocket Simulation application to AMPI. Our experience shows that with a minimal overhead and effort, one can incorporate dynamic load balancing capabilities in legacy Fortran-MPI codes.