An Experimental Evaluation of Workload Driven DVFS

Modern processors support dynamic voltage and frequency scaling (DVFS) that can be leveraged by BIOS or OS drivers to regulate energy consumed in run-time. In this paper, we describe the results of a study that explores the effectiveness of the existing DVFS governors by measuring performance, energy efficiency, and the product of performance and energy efficiency (PxEE), when running both the speed and throughput SPEC CPU2017 benchmark suites. We find that the processor operates at the highest clock frequency even when ~90% of all active CPU cycles are stalled, resulting in poor energy-efficiency, especially in the case of memory-intensive benchmarks. To remedy this problem, we introduce two new workload-driven DVFS techniques that utilize hardware events, (i) the percentage of all stalls (FS-Total Stalls) and (ii) the percentage of memory-related stalls (FS-Memory Stalls), linearly mapping them into available clock frequencies every 10 ms. Our experimental evaluation finds that the proposed techniques considerably improve PxEE relative to the case when the processor is running at a fixed, nominal frequency. FS-Total Stalls improves PxEE by ~26% when all benchmarks are considered and ~67% when only memory-intensive benchmarks are considered, whereas FS-Memory Stalls improves PxEE by ~15% and ~41%, respectively. The proposed techniques thus outperform a prior proposal that utilizes cycles per instruction to control clock frequencies (FS-CPI) that improves PxEE by 4% and 9%, respectively.