Power, Thermal, Reliability and Variability Management of Mobile Devices

Today, there are more mobile devices than human beings on the planet. Mobiles execute a wide variety of applications and are expected to perform in many different environments, from the deserts to the mountain tops. Their goal is to meet user’s expectations and deliver high quality of experience. Unfortunately, to achieve this they face a set of interrelated problems. The heterogeneous components that execute varied tasks can drain a battery in a matter of hours. Power dissipation raises the device temperature, which can be a source of discomfort for the user. Temperature stress also dramatically increases the impact of reliability degradation mechanisms on transistors and interconnects, which can lead to early failure. These problems only worsen with CMOS scaling, which reduces the accuracy of the fabrication process and increases the variability in power, performance and degradation rate. Dynamic management mitigates such issuesby adapting the operating conditions at runtime. Strategies have been very well studied for traditional systems like desktops and servers, but unfortunately they cannot be applied to mobiles, because they do not consider user experience. Existing dynamic management for mobiles only begins to target the problems of power and thermal management, and offers limited solutions for reliability and variability management. This is fundamental to guarantee power savings and prevent early failure in a scenario of increasing variability. In this dissertation, we propose the design and real implementation of a novel unified framework for the comprehensive dynamic management of power, temperature, reliability and variability in mobile systems, subject to user experience requirements. We develop novel lightweight solutions for power and thermal management that optimize for both application behavior and battery lifetime. We complement this with our framework for the online emulation of reliability degradation and variability, which enables the development and rapid prototyping of hardware management solutions. We leverage our emulation framework to design and integrate dynamic reliability and variability management for mobile systems. The presented solutions have been implemented and tested on real devices. Our strategy can meet user experience requirements with a selected target battery lifetime extension of at least 25%. Also, it achieves up to 35% savings in power consumption at the device level, with up to 1 year reliability lifetime improvement for a multicore platform and up to 100% of performance improvement on cluster architectures. Finally, on devices affected by variability it achieves up to 160% performance improvement over the state-of-the-art while meeting the lifetime constraints