SHF: Small: AfterBurner: Efficient Performance Scaling via Post-Retirement Processing

University Of Pennsylvania, Philadelphia PA

Investigators

Abstract

The AfterBurner project looks at improving single-thread performance on both simple and high-performance out-of-order cores in an energy efficient way. Aside from explicit parallelism, this is the primary challenge of multi-core architectures going forward. The most energy-efficient way to improve single-thread performance is to accelerate low-performing program regions. This approach yields the greatest benefit. It also has a low cost because it doesnot require high-bandwidth execution, making it applicable to both simple and high-performance cores. Low single-thread performance is caused by squashes due to control and data mis-speculations and by long latency loads and stores which clog the pipeline. AfterBurner unifies two recently proposed techniques---speculative retirement which can efficiently buffer large numbers of completed instructions and selective re-execution which can re-execute dynamically generated program subgraphs to back-patch program state---and uses them to tolerate all four classes of low-performance events. AfterBurner's multi-purpose infrastructure approach to performance reduces cost, simplifies design, and expands applicability to code that suffers from different low-performance events simulatenously. In addition to education and student tarining, the AfterBurner project marks the beginning of a systems research collaboration between Uniersity of Pennsylvania and Drexel computer science departments.