Just-In-Time instruction delivery is a general method for saving energy in a microprocessor by dynamically limiting the number of in-flight instructions. The goal is to save energy by 1) fetching valid instructions no sooner than necessary, avoiding cycles stalled in the pipeline -- especially the issue queue, and 2) reducing the number of fetches and subsequent processing of mis-speculated instructions. A simple algorithm monitors performance and adjusts the maximum number of in-flight instructions at fairly long intervals, 100K instructions in this study. The proposed JIT instruction delivery
scheme provides the combined benefits of more targeted schemes proposed previously. With only a 3% performance degradation, energy savings in the fetch, decode pipe, and issue queue are 10%, 12%, and 40%, respectively.
By: Tejas Karkhanis, James E. Smith, Pradip Bose
Published in: RC22465 in 2002
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