Flexible and Effective Smartphone Energy Management Using Jouler
Despite the fact that current smartphone platforms already incorporate energy measurement tools and multiple energy control mechanisms, smartphone battery lifetimes continue to frustrate users. This is because measurements and mechanisms are of limited utility without policies that utilize them to achieve different energy management goals, such as meeting a lifetime target or providing good performance to a user’s favorite apps. To address this problem we are developing Jouler, a policy framework enabling effective and flexible smartphone energy management.
Managing Energy Consumption
Jouler centralizes all energy management decisions currently made by smartphone platforms or apps into a single energy manager with access to all existing energy measurements and control mechanisms as well as new mechanisms designed to enable cooperative apps. Jouler enables flexible energy management by allowing the energy manager to be implemented as a standard app, deployed using existing app marketplaces, and rated by users.
Our results revealed enormous variation in many factors impacting energy managementOur work on Jouler is inspired by a detailed energy consumption study we conducted on the PhoneLab Smartphone Testbed. Our results revealed enormous variation in many factors impacting energy management: users charge at different frequencies, use apps that consume varying amounts of energy, and expect different battery lifetimes from their smartphones. As a result, no "one size fits all" policy is sufficient to satisfy the needs of all users. And even if battery technologies and smartphone lifetimes improve in the future, managing energy on mobile devices will continue to be an important challenge. Energy management is about more than managing device lifetime—it is about improving performance given limited resources and ensuring that we realize the true potential of transformative mobile smartphones.
To enable flexible energy management Jouler employs the classic systems design principle of separating policy from mechanism.To enable flexible energy management Jouler employs the classic systems design principle of separating policy from mechanism. Current smartphone platforms currently embed both policy—how energy is allocated—and mechanism—how energy is controlled—within the platform itself, resulting in inflexible policies which are difficult to tailor to individual users. Jouler provides a new interface that exposes energy management capabilities to unprivileged apps for the first time, facilitating innovation within the energy management space. As the figure above shows, Jouler allows multiple energy managers to be installed and configured by the user, each potentially using different strategies to achieve different lifetime goals.
Initial results with a small-scale deployment of Jouler have been promising, with six out of seven users able to increase their battery lifetime by using one of a small set of new energy management policies enabled by the Jouler framework. Inspired by this result we are in the process of rolling out Jouler to the entire PhoneLab testbed to conduct a large-scale study.
Our work on energy management using Jouler has also identified a critical missing piece in the energy management puzzle:
a large amount of work in the mobile systems community has focused on measuring energy consumption, little attention has been paid to putting energy
consumption into context by identifying inherent differences between apps—both in terms of functionality and in how valuable they
are to the smartphone user.
As a complementary effort to Jouler’s energy management framework we are beginning to explore the challenge of quantifying app value. Our HotMobile'15 paper identifies the challenge and describes a preliminary—and unsuccessful—attempt to combine value and energy consumption in order to help users prioritize energy allocation on their smartphones.