This Article 
 Bibliographic References 
 Add to: 
PowerNap: An Efficient Power Management Scheme for Mobile Devices
July 2006 (vol. 5 no. 7)
pp. 816-828
We present PowerNap, an OS power management scheme, which can significantly improve the battery life of mobile devices. The key feature of PowerNap is the skipping of the periodic system timer ticks associated with the operating system. On an idle device, this modification increases the time between successive timer interrupts and enables us to put the processor/system into a more efficient low power state. This saves the energy consumed by workless timer interrupts and the excess energy consumed by the processor in less efficient low power states. PowerNap is tightly integrated with the kernel and is designed for optimal control of the latency and energy associated with transitioning in and out of the low power states. We describe an implementation of PowerNap and its impact on system software. Experiments with IBM's WatchPad verify the ability of PowerNap to extend battery life. An analytical model that quantifies the ability of the scheme to reduce power is also presented. The model is in good agreement with experimental results. We apply the model to small form-factor devices which use processors that have a PowerDown state. In such devices, PowerNap may extend battery life by more than 42 percent for small processor workloads and for background power levels below 10 mW.

[1] N. Kamijoh, T. Inoue, C.M. Olsen, M.T. Raghunath, and C. Narayanaswami, “Energy Trade-Offs in the IBM Wristwatch Computer,” Proc. Int'l Symp. Wearable Computing, pp. 133-140, 2001.
[2] C.M. Olsen, B. Brock, R. Snyder, and M. Ware, “Analysis of Transition Energy and Latency of the PowerDown State in Advanced System-On-a-Chip Processors, ” IBM Research Report RC22970, Nov. 2003.
[3] Cirrus Logic, “EP7211: Data Sheet,” May 1999.
[4] Hitachi, “SH7750 Series: Hardware Manual,” July 2002.
[5] NEC, “Vr4181: User's Manual,” Sept. 2000.
[6] Intel, “Intel PXA250 and PXA210 Applications Processors: Developer's Manual,” Feb. 2002.
[7] K.J. Nowka et al., “A 32-Bit PowerPC System-On-a-Chip with Support for Dynamic Voltage Scaling and Dynamic Frequency Scaling,” IEEE J. Solid State Circuits, vol. 37, no. 11, pp. 1441-1447, Nov. 2002.
[8] N.S. Kim et al., “Leakage Current: Moore's Law Meets Static Power,” Computer, pp. 68-75, Dec. 2003.
[9] S.M. Sze, Semiconductor Devices: Physics and Technology. J. Wiley & Sons, 1985.
[10] Cirrus Logic, EP7312: Data Sheet, May 2002.
[11] Intel, “Intel StrongARM SA-11100 Microprocessor for Portable Applications,” Brief Data Sheet, Apr. 2000.
[12] C.M. Olsen and C. Narayanaswami, “A Work Dependent OS Timing Scheme for Power Management: Implementation in Linux and Modeling of Energy Savings,” IBM Research Report RC 22784, Apr. 2003.
[13] D. Linden, Handbook of Batteries, second ed. McGraw-Hill, 1994.
[14] Micron, “256Mb: x32 Mobile SDRAM,” MT48H8M32LF Advance Datasheet, 2003.
[15] Compaq, Intel, Microsoft, Phoenix, and Toshiba Corporations, “Advanced Configuration and Power Interface Specification,” Rev.2.0c, Aug. 2003.
[16], Jan. 2003. Search for ”enabling power management.”
[17] V. Yodaiken and M. Barabanov, “A Real-Time Linux,” Proc. USENIX Ann. Technical Conf., 1997.
[18] M.B. Srivastava, A.P. Chandrakasan, and RW. Brodersen, “Predictive System Shutdown and Other Architectural Techniques for Energy Efficient Programmable Computation,” IEEE Trans. Very Large Scale Integration Systems, vol. 4, no. 1, p. 42, Mar. 1996.
[19] L.S. Brakmo, D.A. Wallach, and M.A. Viredaz, “uSleep: A Technique for Reducing Energy Consumption in Handheld Devices,” Proc. Second Int'l Conf. Mobile Systems, Applications, and Services (MobiSys), June 2004.
[20] J. Flinn and M. Satyanarayanan, “Energy-Aware Adaptation for Mobile Applications,” Proc. 17th ACM Symp. Operating Systems Principles, pp. 48-63, 1999.
[21] H. Zeng, X. Fan, C. Ellis, A. Lebeck, and A. Vahdat, “ECOSystem: Managing Energy as a First Class Operating System Resource,” Proc. Architectural Support for Programming Languages and Operating Systems Conf., pp. 123-132, Oct. 2002.
[22] M. Weiser, B. Welch, A. Demers, and S. Shenker, “Scheduling for Reduced CPU Energy,” Proc. Symp. Operating Systems Design and Implementation, pp. 13-23, 1994.
[23] D. Grunwald, P. Levis, C. Morrey III, M. Neufeld, and K. Farkas, “Policies for Dynamic Clock Scheduling,” Proc. Symp. Operating Systems Design and Implementation, pp 78-86, Oct. 2000.
[24] Y.-H. Lu, L. Benini, and G.D. Micheli, “Low Power Task Scheduling for Multiple Devices,” Proc. Int'l Workshop Hardware/Software Codesign, pp. 39-43, 2000.
[25] A Vahdat, T. Anderson, M. Dahlin, E. Belani, D. Culler, P. Eastham, and C. Yoshikawa, “WebOS: Operating System Services for Wide Area Applications,” Proc. Seventh IEEE Symp. High Performance Distributed Systems, pp. 52-63, July 1998.
[26] R. Balan, J. Flinn, M. Satyanarayanan, and S. Sinnamohideen, “The Case for Cyber Foraging,” Proc. 10th ACM SIGOPS European Workshop, Sept. 2002.
[27] J. Lorch and A.J. Smith, “Software Strategies for Portable Computer Energy Management,” IEEE Personal Comm. Magazine, vol. 5, no. 3, pp. 60-73, June 1998.
[28] S. Vaddagiri, A.K. Santhanam, V. Sukthankar, and M. Iyer, “Power Management in Linux-Based Systems,” Linux J., Mar. 2004, http://www.linuxjournal.comarticle.php?sid=6699 .
[29] W. Oney, “Programming the Microsoft Windows Driver Model,” second ed. Microsoft Press, 2003.

Index Terms:
Power management, operating systems, mobile systems, processors.
C. Michael Olsen, Chandra Narayanaswami, "PowerNap: An Efficient Power Management Scheme for Mobile Devices," IEEE Transactions on Mobile Computing, vol. 5, no. 7, pp. 816-828, July 2006, doi:10.1109/TMC.2006.103
Usage of this product signifies your acceptance of the Terms of Use.