Joint local and global hardware adaptations for energy

This work concerns algorithms to control energy-driven architecture adaptations for multimedia applications, without and with dynamic voltage scaling (DVS). We identify a broad design space for adaptation control algorithms based on two attributes: (1) when to adapt or temporal granularity and (2) what structures to adapt or spatial granularity. For each attribute, adaptation may be global or local. Our previous work developed a temporally and spatially global algorithm. It invokes adaptation at the granularity of a full frame of a multimedia application (temporally global) and considers the entire hardware configuration at a time (spatially global). It exploits inter-frame execution time variability, slowing computation just enough to eliminate idle time before the real-time deadline. This paper explores temporally and spatially local algorithms and their integration with the previous global algorithm. The local algorithms invoke architectural adaptation within an application frame to exploit intra-frame execution variability, and attempt to save energy without affecting execution time. We consider local algorithms previously studied for non-real-time applications as well as propose new algorithms. We find that, for systems without and with DVS, the local algorithms are effective in saving energy for multi-media applications, but the new integrated global and local algorithm is best for the systems and applications studied.