Energy-Efficient Issue Queue Design

Dmitry Ponomarev, Gurhan Kucuk, Oguz Ergin, Kanad Ghose and Peter M. Kogge
IEEE Transactions on Very Large Scale Integration (VLSI) Systems, Vol. 11, No.5, October 2003, pp.789-800.

Abstract

The out-of-order issue queue (IQ), used in modern superscalar processors is a considerable source of energy dissipation. We consider design alternatives that result in significant reductions in the power dissipation of the IQ (by as much as 75%) through the use of: (a) comparators that dissipate energy mainly on a tag match, (b) zero-byte encoding of operands to imply the presence of bytes with all zeros and, (c) bitline segmentation. Our results are validated by the execution of SPEC 95 benchmarks on a true hardware level, cycle-by-cycle simulator for a superscalar processor and SPICE measurements for actual layouts of the IQ in a 0.18 micron CMOS process.

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