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Power Reduction Through Measurement and Modeling of Users and CPUs Bin Lin, Arindam Mallik, Peter A. Dinda, Gokhan Memik and Robert P. Dick Department of EECS, Northwestern University {b-lin, arindam, pdinda, g-memik, dickrp}@northwestern.edu Our work targets power reduction in laptops. Almost all of them use a version of DVFS (Dynamic Voltage and Frequency Scaling). DVFS is an energy-saving technique that consists of varying the frequency and voltage of a microprocessor in real-time according to processing needs. Specifically, existing DVFS techniques select an operating point (CPU frequency and voltage) based on the utilization of the processor. User-driven Frequency Scaling (UDFS) Current DVFS techniques are pessimistic about the user • Most DVFS schemes (e.g., Windows) is only based on CPU utilization • Leads to use of higher frequencies than necessary for satisfactory performance Process-driven Voltage Scaling (PDVS) User-driven Frequency Scaling (UDFS) • User presses button when annoyed with speed of computer • Button-press feedback drives model & algorithm that drive frequency setting • System adapts to users quickly, leading to a reduced rate of button presses • Two adaptive algorithms Different users have different requirements! Current DVFS techniques are pessimistic about the processor • Assume worst-case manufacturing process variation and operating temperature Voltage set for a particular frequency based on loose worst-case bounds given by the processor manufacturer. Leads to higher voltages than necessary for stable operation, especially in low temperatures. Minimum Stable Voltage (MSV) • Supply voltage that guarantees correct execution for given processing and environmental conditions. • Processors can act flawlessly at lower supply voltages. The extra slack is present due to process variation and temperature. UDFS1 scheme Example: minimum stable Vdd for different operating frequencies & temperatures in an IBM Laptop Process-driven Voltage Scaling (PDVS) • Customize frequency to voltage mapping to individual processor at every temperature, taking advantage of process variation. •An automatic voltage profiler is under development UDFS2 scheme User study • 4 interaction applications: Windows, Microsoft PowerPoint plus music, 3D Shockwave animation video, and FIFA 2005 • 20 users: “Power User”, “Typical User”, and “Beginner” • 2 adaptive algorithms: UDFS1 and UDFS2. % improvement PowerPoint Apps Results (UDFS + PDVS) PowerPoint App Average number of user events 3D Shockwave Measurement 1. Used a control agent in Windows to log system frequency and User events during the study 2. Built a framework to measure the power consumption of a notebook while replaying the user study scenario. • Power numbers presented are original savings- not analytical improvements 3D Shockwave FIFA game Summary of results • Combination of PDVS and the best UDFS scheme reduces measured system power by 49.9% (27.8% PDVS, 22.1% UDFS), averaged across 20 users and 4 representative applications, compared to the Windows XP DVFS scheme. • For multitasking environment, power consumption gets reduced by 58.6% and 75.7% by (UDFS1+PDVS) and (UDFS2+PDVS). • Average temperature reductions for all three applications – 13.2◦C. • This work is in process of technical transfer “User-Driven Frequency Scaling”, IEEE Computer Society Computer Architecture Letters, 2006. Publications: “Process and User Driven Dynamic Voltage and Frequency Scaling”, Tech. Report NWU-EECS-06-11, EECS Department, Northwestern Univ., Aug. 2006. "Power Reduction Through Measurement and Modeling of Users and CPUs", ACM SIGMETRICS 2007 FIFA game % improvement Chebyshev bound-based (1 − p) values for difference of means from zero are also shown Power improvement in the multitasking environment