GreenEr Mobile Systems by Cross LAyer Integrated energy Management

Personal computing currently faces a rapid trend from desktop machines towards mobile services, accessed via tablets, smart phones, and similar terminal devices. With respect to compute power, today`s handheld devices are similar to Cray-2 supercomputers from the 1980s. Due to higher computational load (e.g. via multimedia apps) and the variety of radio interfaces (such as WiFi, 3G, and LTE), modern terminals are getting more and more energy hungry. For instance, a single UMTS upload or a video recording process on today`s smart phones may consume as much as 1.5 Watts, i.e. roughly 50% of the maximal device power. In the near future, higher data rates and traffic, advanced media codecs, and graphics applications will ask for more energy than the battery can deliver. At the same time, the power density limit might lead to a significant share of "Dark Silicon" at 22nm CMOS and below. Obviously, disruptive energy optimizations are required that go well beyond traditional technologies like DVFS (dynamic voltage and frequency scaling) and power-down of temporarily unused components. The GEMSCLAIM project aims at novel approaches for reducing the "greed for energy", thereby improving the user experience and enabling new opportunities for mobile computing. The focus is on three novel approaches: (1) cross layer energy optimization, ranging from the compiler over the operating system down to the target HW platform, (2) efficient programming support for energy-optimized heterogeneous Multicore platforms based on energy-aware service level agreements (SLAs) and energy-sensitive tunable parameters, and (3) introducing energy awareness into Virtual Platforms for the purpose of dynamically customizing the HW architecture for energy optimization and online energy monitoring and accounting. GEMSCLAIM will provide new methodologies and tools in these domains and will quantify the potential energy savings via benchmarks and a HW platform prototype.

Mobile computing devices such as laptops, tablets and smartphones are becoming more widespread. The performance that these devices offer is increasing at a steady pace, with increasing number of processors powering contemporary smartphones. However, mobility comes at a price: energy is a scarce resource on these devices, especially with power-hungry media consumption constituting a major use case. Furthermore, mobile computing is not the sole field where energy is increasingly relevant - the tremendous increase in power consumption by performance-oriented servers has made power budgeting unavoidable in HPC as well. Several solutions have been proposed to address the energy problem on different levels. While system-level approaches have been explored to a certain extent, we believe there still exists a lot of room for improvement on the application level since no power management interface that can be considered complete, generic and easy to use has been proposed so far. GEMSCLAIM explored application-level energy saving opportunities through the specification, implementation and evaluation of OpenMPE an OpenMP extension for Energy. OpenMPE adds new directives and clauses to enable per-region customization of multiple optimization objectives and tunable parameters. GEMSCLAIM resulted in three major contributions: A novel API for application-level energy-aware programming, allowing programmers to expose energy saving opportunities through i) characterizing application behavior by providing a semantic program region structure, ii) setting per-code region multi-objective goals, and iii) exposing application-level tunable parameters. A compilation and runtime system supporting OpenMPE. The runtime system exploits opportunities exposed by programmers through several techniques such as dynamic voltage and frequency scaling, dynamic concurrency throttling (DCT), and application-level content adaptation. An empirical evaluation of the effectiveness of OpenMPE. A video codec reference implementation has been enriched with OpenMPE and benchmarked on a desktop and mobile platform. GEMSCLAIM thus contributed important research results that can lead to substantial improvement in saving energy for mobile systems.