Amdahl’s Law Revisited for Single Chip Systems

Amdahl’s Law is based upon two assumptions – that of boundlessness and homogeneity – and so it can fail when applied to single chip heterogeneous multiprocessor designs, and even microarchitecture. We show that a perfor-mance increase in one part of the system can negatively impact the overall performance of the system, in direct contradiction to the way Amdahl’s Law is instructed. Fundamental assumptions that are consistent with Amdahl’s Law are a heavily ingrained part of our computing design culture, for research as well as design. This paper points in a new direction. We moti-vate that emphasis should be made on holistic, system level views instead of divide and conquer approaches. This, in turn, has relevance to the poten-tial impacts of custom processors, system-level scheduling strategies and the way systems are partitioned. We realize that Amdahl’s Law is one of the few, fundamental laws of computing. However, its very power is in its simplicity, and if that simplicity is carried over to future systems, we believe that it will impede the potential of future computing systems. KEY WORDS: Amdahl’s Law; single chip heterogeneous multiprocessing; performance; design; partitioning. 1