Energy optimal speed control of devices with discrete speed sets

Ravishankar Rao, Sarma Vrudhula

Research output: Chapter in Book/Report/Conference proceedingConference contribution

6 Scopus citations


We obtain analytically, the energy optimal speed profile of a generic multi-speed device with a discrete set of speeds, to execute a given task within a given time. Current implementations of energy efficient speed control policies (including DVFS) almost exclusively use the minimum feasible speed pair, which has been shown before to be suboptimal. Unlike previous works, ours does not require an explicit functional relationship between the device's power and speed (e.g. the CMOS power model), but only assumes that the power-speed relationship is a W-convex (a discrete equivalent of a convex) function. This assumption allowed us to show that the optimal speed profile uses at most two speeds, and that all the essential characteristics of the power-speed relationship can be encapsulated within a single speed, ω u. The latter speed is intrinsic to the device (i.e. task independent) and can be readily computed from its power-speed values (without any curve fit). Further, ω u is also the speed at which the the device consumes the least energy per unit work done. The problem formulation reduces to a linear program in the number of supported speeds, which in general, is difficult to solve analytically. However, the optimum solution has a very simple form - it is either ω u, or the minimum feasible speed pair for the given task. We verified that a number of commercial DVFS processors, and other devices like disk drives satisfied our model of the W-convex power-speed relationship.

Original languageEnglish (US)
Title of host publicationProceedings - Design Automation Conference
Number of pages4
StatePublished - 2005
Event42nd Design Automation Conference, DAC 2005 - Anaheim, CA, United States
Duration: Jun 13 2005Jun 17 2005


Other42nd Design Automation Conference, DAC 2005
Country/TerritoryUnited States
CityAnaheim, CA


  • Convex functions
  • Energy optimization
  • Frequency scaling
  • Low-power
  • Speed control
  • Voltage scaling

ASJC Scopus subject areas

  • Hardware and Architecture
  • Control and Systems Engineering


Dive into the research topics of 'Energy optimal speed control of devices with discrete speed sets'. Together they form a unique fingerprint.

Cite this