SHF: Small: Collaborative Research: ShapeShifting and PubSub for Tailoring Memory Accesses and Communication in Heterogeneous Multiprocessors

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Over the past decade or more, microprocessors have faced increasing challenges in achieving high-performance for current and emerging software applications while abiding by severe power and thermal limits. In response, industry has turned to approaches that use specialized graphics and computational hardware and complex memory organizations. The end result is that computer systems have become more heterogeneous and complex, in ways that make it difficult for programmers to write efficient and high-performance software. Software tuned to run on one implementation will often not run at all or will perform poorly or unpredictably when ported to even a different implementation in the same chip family. The objective of this research effort is to design and evaluate system and hardware support that tailors memory and data access/movements to improve performance and power efficiency, while also easing the issues of programmability and of tuning software for individual chip characteristics.The two key themes of this work are Shape Shifting and PubSub data abstractions. ShapeShifting refers to optimizations and hardware support structures that allow data to be transformed in layout, in order to support faster access, more efficient use of memory, and other attributes that improve power and performance. In some preliminary experiments, even a software-only implementation of Shape Shifting improves performance by 15%. Pub Sub data abstractions offer methods for individual processors to indicate interest (or disinterest) in updates regarding other program variables. These abstractions form the underpinning for memory optimizations that are tailored to the application?s memory usage patterns. By mitigating false sharing, encouraging coarse-grained fetches, and reducing coherence broadcasts to uninterested cores, PubSub has the potential to improve the power and performance efficiency of multi-core implementations by a factor of 2X or more.The research program is targeting several types of broad impact. First, the simulators and tools developed by this project will be released as free, open-source software. Second, the results can enhance performance and energy efficiency of future parallel hardware. Energy-efficiency is of particular concern from a national economic and strategic standpoint, given the growing electricity consumption of computer systems and the important role of the memory hierarchy in influencing computer power consumption.