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The Liberty Research Group

Microarchitecture Modeling for Design-space Exploration [abstract] (PDF)
Manish Vachharajani
Ph.D. Thesis, Department of Electrical Engineering, Princeton University, November 2004.

To identify the best processor designs, designers explore a vast design space. To assess the quality of candidate designs, designers construct and use simulators. Unfortunately, simulator construction is a bottleneck in this design-space exploration because existing simulator construction methodologies lead to long simulator development times. This bottleneck limits exploration to a small set of designs, potentially diminishing quality of the final design.

This dissertation describes a method to rapidly construct high-quality simulators. In particular, it examines structural modeling as a means to reduce construction time because it eliminates redundant effort required to manage design complexity in many modeling approaches, including that of programming a simulator in a sequential language. The dissertation also describes how to overcome common limitations in structural modeling that increase construction time by precluding amortization of component specification effort across models via component-based reuse. First, some time-consuming to specify design portions do not benefit from reuse, the logic for managing stall signals (i.e., timing-control) chief among them. Second, components flexible enough to enjoy reuse are often not reused in practice because of the number of details that must be understood in order to instantiate them. This dissertation addresses these issues by:

  • Presenting new insight into timing-control that allows it to be partitioned amongst reusable components.
  • Describing the application of programming language techniques (such as polymorphism and aspect-oriented programming) to allow creation of easy to reuse flexible components.
  • Allowing models to be statically analyzable in the presence of the above features.

The techniques presented in this dissertation are embodied in the Liberty Simulation Environment (LSE). LSE users have seen over an order of magnitude reduction in model development time. Their models were of high-quality; they were accurate, had adequate simulation speeds, and were compatible with static techniques for visualization and optimization.

Short model construction times allow more ideas to be explored in less time. This leads to shorter product time-to-market and more thorough design-space exploration. This also allows researchers to evaluate new design ideas faster, to efficiently evaluate ideas in the context of many designs, and, perhaps, develop a more fundamental understanding of microarchitecture due to these broader evaluations.