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A highly efficient fetch unit is essential not only to obtain good performance but also to achieve energy efficiency. However, existing commercial fetch designs are not adaptable and depending on the program behaviour, they can be either insufficient or an overkill. A phase-based adaptive fetch mechanism that can be dynamically adjusted based on feedback information of the program behaviour is introduced. This design adds very little hardware complexity and relegates complex tasks to the software components. It is also very effective: saving 35% and 52% fetch energy on an average compared with a conventional and a trace cache-based fetch unit, respectively. At the same time, performance is improved by 4.7% and 0.8%, respectively.
Date of Publication: March 2008