Electrical Engineering
      and Computer Sciences

Electrical Engineering and Computer Sciences

COLLEGE OF ENGINEERING

UC Berkeley

Reducing Processor Power Consumption by Improving Processor Time Management in a Single-User Operating System

Jacob R. Lorch and Alan Jay Smith

EECS Department
University of California, Berkeley
Technical Report No. UCB/CSD-96-914
September 1996

http://www.eecs.berkeley.edu/Pubs/TechRpts/1996/CSD-96-914.pdf

The CPU is one of the major power consumers in a portable computer, and considerable power can be saved by turning off the CPU when it is not doing useful work. In Apple's MacOS, however, idle time is often converted to busy waiting, and generally it is very hard to tell when no useful computation is occurring. In this paper, we suggest several heuristic techniques for identifying this condition, and for temporarily putting the CPU in a low-power state. These techniques include turning off the processor when all processes are blocked, turning off the processor when processes appear to be busy waiting, and extending real time process sleep periods. We use trace-driven simulation, using processor run interval traces, to evaluate the potential energy savings and performance impact. We find that these techniques save considerable amounts of processor energy (as much as 66%), while having very little performance impact (less than 2% increase in run time). Implementing the proposed strategies should increase battery lifetime by approximately 20% relative to Apple's current CPU power management strategy, since the CPU and associated logic are responsible for about 32% of power use; similar techniques should be applicable to operating systems with similar behavior.


BibTeX citation:

@techreport{Lorch:CSD-96-914,
    Author = {Lorch, Jacob R. and Smith, Alan Jay},
    Title = {Reducing Processor Power Consumption by Improving Processor Time Management in a Single-User Operating System},
    Institution = {EECS Department, University of California, Berkeley},
    Year = {1996},
    Month = {Sep},
    URL = {http://www.eecs.berkeley.edu/Pubs/TechRpts/1996/5817.html},
    Number = {UCB/CSD-96-914},
    Abstract = {The CPU is one of the major power consumers in a portable computer, and considerable power can be saved by turning off the CPU when it is not doing useful work. In Apple's MacOS, however, idle time is often converted to busy waiting, and generally it is very hard to tell when no useful computation is occurring. In this paper, we suggest several heuristic techniques for identifying this condition, and for temporarily putting the CPU in a low-power state. These techniques include turning off the processor when all processes are blocked, turning off the processor when processes appear to be busy waiting, and extending real time process sleep periods. We use trace-driven simulation, using processor run interval traces, to evaluate the potential energy savings and performance impact. We find that these techniques save considerable amounts of processor energy (as much as 66%), while having very little performance impact (less than 2% increase in run time). Implementing the proposed strategies should increase battery lifetime by approximately 20% relative to Apple's current CPU power management strategy, since the CPU and associated logic are responsible for about 32% of power use; similar techniques should be applicable to operating systems with similar behavior.}
}

EndNote citation:

%0 Report
%A Lorch, Jacob R.
%A Smith, Alan Jay
%T Reducing Processor Power Consumption by Improving Processor Time Management in a Single-User Operating System
%I EECS Department, University of California, Berkeley
%D 1996
%@ UCB/CSD-96-914
%U http://www.eecs.berkeley.edu/Pubs/TechRpts/1996/5817.html
%F Lorch:CSD-96-914