STFL: Energy-Efficient Data Movement with Slow Transition Fast Level Signaling

Data movement in large caches consumes a significant amount of energy in modern computer systems. Low power interfaces have been proposed to address this problem. Unfortunately, the energy-efficiency of these techniques is largely limited due to undue latency overheads of low power wires and complex coding mechanisms. This paper proposes a hybrid technique for slow-transition, fast-level (STFL) signaling that creates a balance between power and bandwidth in the last level cache interface. Combined with STFL codes, the signaling technique significantly mitigates the performance impacts of low power wires, thereby improving the energy efficiency of data movement in memory systems. When applied to the last level cache of a contemporary multicore system, STFL improves the CPU energy-delay product by 9% as compared to a voltage-frequency scaled baseline. Moreover, the proposed architecture reduces the CPU energy by 26% and achieves 98% of the performance provided by a high-performance baseline.