Tradeoffs in power-efficient issue queue design

A major consumer of microprocessor power is the issue queue. Several microprocessors, including the Alpha 21264 and POWER4™, use a compacting latch-based issue queue design which has the advantage of simplicity of design and verification. The disadvantage of this structure, however, is its high power dissipation. In this paper, we explore different issue queue power optimization techniques that vary not only in their performance and power characteristics, but in how much they deviate from the baseline implementation. By developing and comparing techniques that build incrementally on the baseline design, as well as those that achieve higher power savings through a more significant redesign effort, we quantify the extra benefit the higher design cost techniques provide over their more straightforward counterparts.