Optimizing irregular applications for energy and performance on the Tilera many-core architecture

Optimizing applications simultaneously for energy and performance is a complex problem. High performance, parallel, irregular applications are notoriously hard to optimize due to their data-dependent memory accesses, lack of structured locality and complex data structures and code patterns. Irregular kernels are growing in importance in applications such as machine learning, graph analytics and combinatorial scientific computing. Performance- and energy-efficient implementation of these kernels on modern, energy efficient, many-core platforms is therefore an important and challenging problem. We present results from optimizing two irregular applications -- the Louvain method for community detection (Grappolo), and high-performance conjugate gradient (HPCCG) -- on the Tilera many-core system. We have significantly extended MIT's OpenTuner auto-tuning framework to conduct a detailed study of platform-independent and platform-specific optimizations to improve performance as well as reduce total energy consumption. We explore the optimization design space along three dimensions: memory layout schemes, compiler-based code transformations, and optimization of parallel loop schedules. Using auto-tuning, we demonstrate whole-node energy savings of up to 41% relative to a baseline instantiation, and up to 31% relative to manually optimized variants.