Increasing power dissipation has become a major constraint for future performance gains in the design of microprocessors. In this paper, we present the circuit design of an issue queue for a superscalar processor that leverages transmission gate insertion to provide dynamic low-cost configurability of size and speed. A novel circuit structure dynamically gathers statistics of issue queue activity over intervals of instruction execution. These statistics are then used to change the size of an issue queue organization on-the-fly to improve issue queue energy and performance. When applied to a fixed, full-size issue queue structure, the result is up to 70 % reduction in energy dissipation. The complexity of the additional circuitry to achieve this result is almost negligible. Furthermore, self-timed techniques embedded in the adaptive scheme can provide a 56 % decrease in cycle time of the issue queue when we change the adaptive issue queue size from 32 entries (largest possible) to 8 entries (smallest possible in our design).
By: Alper Buyuktosunoglu, Stanley Schuster, David Brooks, Pradip Bose, Peter Cook, David Albonesi (University of Rochester)
Published in: RC21874 in 2000
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