Impact of DVFS on n-Tier Application Performance

Dynamic Voltage and Frequency Scaling (DVFS) has been widely deployed and proven to reduce energy consumption at low CPU utilization levels; however, our measurements of the n-tier application bench-mark (RUBBoS) performance showed significant per-formance degradation at high utilization levels, with re-sponse time several times higher and throughput loss of up to 20%, when DVFS is turned on. Using a combi-nation of benchmark measurements and simulation, we found two kinds of problems: large response time fluc-tuations due to push-back wave queuing in n-tier sys-tems and throughput loss due to rapidly alternating bot-tlenecks. These problems arise from anti-synchrony be-tween DVFS adjustment period and workload burst cy-cles (similar cycle length but out of phase). Simulation results (confirmed by extensive measurements) show the anti-synchrony happens routinely for a wide range of configurations. We show that a workload-sensitive DVFS adaptive control mechanism can disrupt the anti-synchrony and reduce the performance impact of DVFS at high utilization levels to 25 % or less of the original.