Design and Evaluation of Multi-threaded Optimizations for Individual MPI I/O Operations

Todays high-end parallel clusters are architecturally very complex. Most large scale applications nowadays are utilizing multiple parallel programming paradigms to achieve the required scalability, with MPI+threads being the most common approach. Yet, as of today, there is no parallel I/O library that matches this hybrid programming model. File I/O operations are typically executed by a single thread for each process. This paper explores multi-threaded optimizations for individual MPI I/O operations, an important step towards matching the execution model of modern parallel applications. We describe the changes necessary to the internal processing in the MPI I/O library as well as to the file access phase. We demonstrate the performance improvement of the redesigned functions using multiple benchmarks and on multiple platforms for many scenarios over the original, single-threaded version.