A survey of power management techniques in mobile computing operating systems
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paper_title: The challenges of mobile computing

paper_content:

The technical challenges that mobile computing must surmount to achieve its potential are hardly trivial. Some of the challenges in designing software for mobile computing systems are quite different from those involved in the design of software for today's stationary networked systems. The authors focus on the issues pertinent to software designers without delving into the lower level details of the hardware realization of mobile computers. They look at some promising approaches under investigation and also consider their limitations. The many issues to be dealt with stem from three essential properties of mobile computing: communication, mobility, and portability. Of course, special-purpose systems may avoid some design pressures by doing without certain desirable properties. For instance portability would be less of a concern for mobile computers installed in the dashboards of cars than with hand-held mobile computers. However, the authors concentrate on the goal of large-scale, hand-held mobile computing as a way to reveal a wide assortment of issues. >
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paper_title: Thwarting the Power Hungry Disk

paper_content:

Minimizing power consumption is important for mobile computers, and disks consume a significant portion of system-wide power. There is a large difference in power consumption between a disk that is spinning and one that is not, so systems try to keep the disk spinning only when it must. The system must trade off between the power that can be saved by spinning the disk down quickly after each access and the impact on response time from spinning it up again too often. We use trace-driven simulation to examine these trade-offs, and compare a number of different algorithms for controlling disk spin-down. We simulate disk accesses from a mobile computer (a Macintosh Powerbook Duo 230) and also from a desktop workstation (a Hewlett-Packard 9000/845 personal workstation running HP-UX), running on two disks used on mobile computers, the Hewlett-Packard Kittyhawk C3014A and the Quantum Go•Drive 120. We show that the "perfect" off-line algorithm--one that consumes minimum power without increasing response time relative to a disk that never spins down--can reduce disk power consumption by 35--50%, compared to the fixed threshold suggested by manufacturers. An on-line algorithm with a threshold of 10 seconds, running on the Powerbook trace and Go•Drive disk, reduces energy consumption by about 40% compared to the 5-minute threshold recommended by manufacturers of comparable disks; however, over a 4-hour trace period it results in 140 additional delays due to disk spin-ups.
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paper_title: A Quantitative Analysis of Disk Drive Power Management in Portable Computers

paper_content:

With the advent and subsequent popularity of portable computers, power management of system components has become an important issue. Current portable computers implement a number of power reduction techniques to achieve a longer battery life. Included among these is spinning down a disk during long periods of inactivity. In this paper, we perform a quantitative analysis of the potential costs and benefits of spinning down the disk drive as a power reduction technique. Our conclusion is that almost all the energy consumed by a disk drive can be eliminated with little loss in performance. Although on current hardware, reliability can be impacted by our policies, the next generation of disk drives will use technology (such as dynamic head loading) which is virtually unaffected by repeated spinups. We found that the optimal spindown delay time, the amount of time the disk idles before it is spun down, is 2 seconds. This differs significantly from the 3-5 minutes in current practice by industry. We will show in this paper the effect of varying the spindown delay on power consumption; one conclusion is that a 3-5 minute delay results in only half of the potential benefit of spinning down a disk.
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paper_title: A Quantitative Analysis of Disk Drive Power Management in Portable Computers

paper_content:

With the advent and subsequent popularity of portable computers, power management of system components has become an important issue. Current portable computers implement a number of power reduction techniques to achieve a longer battery life. Included among these is spinning down a disk during long periods of inactivity. In this paper, we perform a quantitative analysis of the potential costs and benefits of spinning down the disk drive as a power reduction technique. Our conclusion is that almost all the energy consumed by a disk drive can be eliminated with little loss in performance. Although on current hardware, reliability can be impacted by our policies, the next generation of disk drives will use technology (such as dynamic head loading) which is virtually unaffected by repeated spinups. We found that the optimal spindown delay time, the amount of time the disk idles before it is spun down, is 2 seconds. This differs significantly from the 3-5 minutes in current practice by industry. We will show in this paper the effect of varying the spindown delay on power consumption; one conclusion is that a 3-5 minute delay results in only half of the potential benefit of spinning down a disk.
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paper_title: Predictive power conservation

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In the case of a hard disk in a laptop, the restart cost is considerable: the disk has to be spun up to speed again, recalibratedl and made ready to execute commands. This takes between 2.5 and 6 seconds for typical 2.5" hard disk drives. During this time, the system is locked up waiting for the I/O to complete. The power costs are also high: on a representative Quantum 2.5" drive, spinningup the drive requires 5Wfor 1 second, followed by 1.5W for a 1 second calibration pass.
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paper_title: Energy efficient indexing on air

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We consider wireless broadcasting of data as a way of disseminating information to a massive number of users. Organizing and accessing information on wireless communication channels is different from the problem of organizing and accessing data on the disk. We describe two methods, (1, m ) Indexing and Distributed Indexing , for organizing and accessing broadcast data. We demonstrate that the proposed algorithms lead to significant improvement of battery life, while retaining a low access time.
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paper_title: Dealing with Mobility: Issues and Research Challenges

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Recent advances in hardware and communication technology have made mobile computing possible. It is expected, [BIV92], that in the near future, tens of millions of users will carry a portable computer with a wireless connection to a worldwide information network. This rapidly expanding technology poses new challenging problems. The mobile computing environment is an environment characterized by frequent disconnections, significant limitations of bandwidth and power, resource restrictions and fast-changing locations. The peculiarities of the new environment make old software systems inadequate and raise new challenging research questions. In this report we attempt to investigate the impact of mobility on the todays software systems, report on how research starts dealing with mobility and state some problems that remain open.
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Title: A survey of power management techniques in mobile computing operating systems

Section 1: Introduction
Description 1: Introduce the motivation and scope of power management techniques in mobile computing.

Section 2: CPU Power Consumption
Description 2: Discuss techniques and algorithms for managing and reducing CPU power consumption.

Section 3: Hard Drive Power Consumption
Description 3: Analyze methods for controlling and reducing power consumption of hard drives in mobile devices.

Section 4: Power and Wireless Communication
Description 4: Explore techniques for managing power consumption related to wireless communication and data broadcast.

Section 5: Scheduling for Reduced CPU Energy
Description 5: Examine the specifics of Weiser et al.'s work on algorithms for adjusting CPU clock speed to save power.

Section 6: Disk Drive Power Management
Description 6: Review different strategies and analyses for reducing power consumption through hard drive spindown and spinup mechanisms.

Section 7: Energy Efficient Indexing on Air
Description 7: Investigate approaches for organizing and accessing broadcast data to optimize power usage in wireless communication.

Section 8: Conclusion
Description 8: Summarize the key findings and implications of using various power management techniques in mobile computing operating systems.