Chained in-order/out-of-order doublecore architecture

Abstract

Complexity is one of the most important problems facing microarchitects. It is exacerbated by the application of optimizations, by scaling to higher issue widths and, in general, by increasing the size of microprocessor structures. This paper presents a new microarchitecture, the chained in-order/out-of-order doublecore architecture (CIO2), designed to attack the problems of complexity and energy. The CIO2 architecture reorganizes the microarchitecture using the concepts of a centralized register file and the future file. The resulting architecture decouples that program state from the execution units. The simplicity of the architecture enables the implementation of three optimizations with little effort: register file banking, writeback filtering and instruction pre-execution. These optimizations allow a reduction of up to 75% in register file energy consumption. Instruction pre-execution further allows around 40% of all integer instructions to execute in the in-order front-end, considerably reducing the activity of the power-hungry issue queues in the out-of-order back-end. Moreover, these improvements are achieved with a negligible performance loss.