Energy-efficient CPU scheduling for multimedia applications

This paper presents the design, implementation, and evaluation of GRACE-OS, an energy-efficient real-time CPU scheduler for multimedia applications running on a mobile device. GRACE-OS seeks to minimize the total energy consumed by the device while meeting multimedia timing requirements. To achieve this goal, GRACE-OS integrates dynamic voltage scaling into the traditional real-time CPU scheduling: It decides at what CPU speed to execute applications in addition to when to execute what applications. GRACE-OS makes these scheduling decisions based on the probability distribution of cycle demand of multimedia applications and obtains their demand distribution via online profiling. We have implemented GRACE-OS in the Linux kernel and evaluated it on a laptop with a variable-speed CPU and typical multimedia codecs. Our experimental results show four findings: First, the demand distribution of our studied codecs is stable or changes slowly. This stability implies the feasibility to perform our proposed energy-efficient scheduling with low overhead. Second, GRACE-OS delivers soft performance guarantees to these codecs by bounding their deadline miss ratio under the application-specific performance requirements. Third, GRACE-OS reduces the total energy of the laptop by 14.4 % to 37.2 % relative to the scheduling algorithm without voltage scaling and by 2 % to 10.5 % relative to voltage scaling algorithms without considering the demand distribution. Finally, GRACE-OS saves energy by 2 % to 5 % by explicitly considering the discrete CPU speeds and the corresponding total power of the whole laptop, rather than assuming continuous speeds and cubic speed-power relationship