Microprocessor Pipeline Energy Analysis

The increase in high-performance microprocessor power con-sumption is due in part to the large power overhead of wide-issue, highly speculative cores. Microarchitectural specula-tion, such as branch prediction, increases instruction through-put but carries a power burden due to wasted power for mis-speculated instructions. Pipeline over-provisioning sup-plies excess resources which often go unused. In this pa-per, we use our detailed performance and power model for an Alpha 21264 to measure both the useful energy and the wasted effort due to mis-speculation and over-provisioning. Our experiments show that flushed instructions account for approximately 6 % of total energy, while over-provisioning imposes a tax of 17 % on average. These results suggest op-portunities for power savings and energy efficiency through-out microprocessor pipelines