@TechReport{	  it:2011-007,
  author	= {Vasileios Spiliopoulos and Stefanos Kaxiras and Georgios
		  Keramidas},
  title		= {A Framework for Continuously Adaptive {DVFS}},
  institution	= {Department of Information Technology, Uppsala University},
  department	= {Division of Computer Systems},
  year		= {2011},
  number	= {2011-007},
  month		= mar,
  abstract	= {We present Continuously Adaptive Dynamic Voltage-Frequency
		  Scaling in Linux systems running on Intel i7 and AMD Phenom
		  II processors. By exploiting slack, inherent in
		  memory-bound programs, our approach aims to improve power
		  efficiency even when the processor does not sit idle. Our
		  underlying methodology is based on a simple first-order
		  processor performance model in which frequency scaling is
		  expressed as a change (in cycles) of the main memory
		  latency. Utilizing available performance monitoring
		  hardware, we show that our model is powerful enough to i)
		  predict with reasonable accuracy the effect of frequency
		  scaling (in terms of performance loss), and ii) predict the
		  energy consumed by the core under different V/f
		  combinations. To validate our approach we perform
		  high-accuracy, fine-grain, power measurements directly on
		  the off-chip voltage regulators. We use our model to
		  implement various DVFS policies as Linux ~green~ governors
		  to continuously optimize for various power- efficiency
		  metrics such as EDP (Energy-Delay Product) or ED2P
		  (Energy-Delay-Square Product), or achieve energy savings
		  with a user-specified limit on performance loss. Our
		  evaluation shows that, for SPEC2006 workloads, our
		  governors achieve dynamically the same optimal EDP or ED2P
		  (within 2\% on average) as an exhaustive search of all
		  possible frequencies and supply voltages. Energy savings
		  can reach up to 56\% in memory-bound workloads with
		  corresponding improvements of about 55\% for EDP or ED2P. }
}