Revisiting reorder buffer architecture for next generation high performance computing

Modern microprocessors achieve high application performance at an acceptable level of power dissipation. Reorder buffer is used for out-of-order instructions to be committed in-order. The reorder buffer plays a key role in modern microprocessors because performance improvement techniques highly rely on aggressive speculation to feed wider issue, out-of-order, and deep pipelines. In terms of power to performance trade-off, reorder buffer is particularly important. This is because enlarging the reorder buffer size achieves high performance but naive scaling of the conventional reorder buffer architecture can severely increase the complexity and power consumption. In this paper, we propose low-power reorder buffer techniques for contemporary microprocessors. First, the separated reorder buffer reduces power dissipation by deferred allocation and early release. The deferred allocation delays the SROB allocation of instructions until all their data dependencies are resolved. Then, the instructions are executed in program order and they are released faster from the SROB. The result of the instruction is written into rename buffers immediately after the execution completes. Then, the result values in the rename buffer are written into the architectural register file at the commit state. The proposed approaches in this paper provide higher resource utilization and low power consumption.