In this paper, we demonstrate that a collaborative relationship between the operating system and applications can be used to meet user-specified goals for battery duration. We first show how applications can dynamically modify their behavior to conserve energy. We then show how the Linux operating system can guide such adaptation to yield a batterylife of desired duration. By monitoring energy supply and demand, it is able to select the correct tradeoff between energy conservation and application quality. Our evaluation shows that this approach can meet goals that extend battery life by as much as 30%.

Dynamic power management (DPM) is a design methodology for dynamically reconfiguring systems to provide the requested services and performance levels with a minimum number of active components or a minimum load on such components. DPM encompasses a set of techniques that achieves energy-efficient computation by selectively turning off (or reducing the performance of) system components when they are idle (or partially unexploited). In this paper, we survey several approaches to system-level dynamic power management. We first describe how systems employ power-manageable components and how the use of dynamic reconfiguration can impact the overall power consumption. We then analyze DPM implementation issues in electronic systems, and we survey recent initiatives in standardizing the hardware/software interface to enable software-controlled power management of hardware components.

Abstract. Wireless networking has witnessed an explosion of interest from consumers in recent years for its applications in mobile and personal communications. As wireless networks become an integral component of the modern communication infrastructure, energy efficiency will be an important design consideration due to the limited battery life of mobile terminals. Power conservation techniques are commonly used in the hardware design of such systems. Since the network interface is a significant consumer of power, considerable research has been devoted to low-power design of the entire network protocol stack of wireless networks in an effort to enhance energy efficiency. This paper presents a comprehensive summary of recent work addressing energy efficient and low-power design within all layers of the wireless network protocol stack.

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Power consumption is the limiting factor for the functionality of future wearable devices. Since interactive applications like wireless information access generate bursts of activities, it is important to match the performance of the wearable device accordingly. This paper describes a system with a microprocessor whose speed can be varied (frequency scaling) as well as its input voltage. Voltage scaling is important for reducing power consumption to very low values when operating at low speeds. Measurements show that the energy per instruction at minimal speed (59 MHz) is 1/5 of the energy required at full speed (251 MHz). The frequency and voltage can be scaled dynamically from user space in only 140 ¡ s. This allows power-aware applications to quickly adjust the performance level of the processor whenever the workload changes. 1

Power-saving is a critical issue for almost all kinds of portable devices. In this paper, we consider the design of power-saving protocols for mobile ad hoc networks (MANETs) that allow mobile hosts to switch to a low-power sleep mode. The MANETs being considered in this paper are characterized by unpredictable mobility, multi-hop communication, and no clock synchronization mechanism. In particular, the last characteristic would complicate the problem since a host has to predict when another host will wake up to receive packets. We propose three power management protocols, namely dominating-awake-interval, periodically-fully-awake-interval, and quorum-based protocols, which are directly applicable to IEEE 802.11based MANETs. As far as we know, the power management problem for multi-hop MANETs has not been seriously addressed in the literature. Existing standards, such as IEEE 802.11, HIPERLAN, and bluetooth, all assume that the network is fully connected or there is a clock synchronization mechanism. Extensive simulation results are presented to verify the effectiveness of the proposed protocols.

A prerequisite of energy-aware scheduling is precise knowledge of any activity inside the computer system. Embedded hardware monitors (e.g., processor performance counters) have proved to offer valuable information in the field of performance analysis. The same approach can be applied to investigate the energy usage patterns of individual threads. We use information about active hardware units (e.g., integer/floatingpoint unit, cache/memory interface) gathered by event counters to establish a thread-specific energy accounting. The evaluation shows that the correlation of events and energy values provides the necessary information for energy-aware scheduling policies. Our approach to OS-directed power management adds the energy usage pattern to the runtime context of a thread. Depending on the field of application we present two scenarios that

this paper, we propose the systematic re-examination of all aspects of operating system design and implementation from the point of view of energy efficiency rather than the more traditional OS metric of maximizing performance. In [7], we made the case for energy as a first-class OS-managed resource. We emphasized the benefits of higher-level control over energy usage policy and the application/OS interactions required to achieve them. This paper explores the implications that this major shift in focus can have upon the services, policies, mechanisms, and internal structure of the OS itself based on our initial experiences with rethinking system design for energy efficiency.

Power and energy are increasingly becoming a limitation for microprocessor design. Modern microprocessors employ a number of techniques to reduce energy consumption. Since modern architectures typically waste activity on speculative execution, prior work has explored micro-architectural mechanisms for speculation control. These techniques attempt to adjust the excess speculation in the micro-architecture, but typically seek heuristics that target an "iso-performance" goal -- power is reduced, but never at the expense of performance. We argue that this strategy will have limited energy savings because the system performance goal is not clearly articulated to the micro-architecture. We propose that software, including a combination of the operating system and applications, should use a performance mechanism to indicate the desired performance and allow the micro-architecture to then choose between extant methods to achieve that performance while reducing power usage. We demons...

The typical duration of multimedia streams makes wireless network interface (WNIC) energy consumption a particularly acute problem for mobile clients. In this work, we explore ways to transmit data packets in a predictable fashion; allowing the clients to transition the WNIC to a lower power consuming sleep state. First, we show the limitations of IEEE 802.11 power saving mode for isochronous multimedia streams. Without an understanding of the stream requirements, they do not offer any energy savings for multimedia streams over 56 kbps. The potential energy savings is also affected by multiple clients sharing the same access point. On the other hand, an application-specific server side traffic shaping mechanism can offer good energy saving for all the stream formats without any data loss. We show that the mechanism can save up to 83% of the energy required for receiving data. The technique offers similar savings for multiple clients sharing the same wireless access point. For high fidelity streams, media players react to these added delays by lowering the stream fidelity. We propose that future media players should offer configurable settings for recognizing such energy-aware packet delay mechanisms.