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K2: a mobile operating system for heterogeneous coherence domains
Lin F., Wang Z., Zhong L.  ACM Transactions on Computer Systems 33 (2): 1-27, 2015. Type: Article
Date Reviewed: Jul 28 2015

Power management is the unsung hero of mobile computing and the limiting frontier of future mobile technology. Improvements in energy usage will expand our horizons past mobile through wearable and on to implantable technology, but first we have to lose the battery.

The K2 operating system (OS) is an incremental advance in reduced energy consumption. New mobile system-on-chips (SoCs) are divided into full-power and reduced-power sections (“coherence domains”) in order to consume less power, but assigning software to the proper domain is difficult. So is communication and movement between those domains as applications change state. K2 simplifies the programming of multiple coherence domains while preserving performance. According to the authors, overhead on their TI OMAP4 SoC was kept to a six percent penalty while light workloads were energy-optimized by a factor of ten (read the paper for specifics).

The authors created this new OS with three goals in mind: ease application development, simplify OS engineering, and preserve performance. They chose a shared-most model where kernel services are replicated in each coherence domain. This means kernel services look the same to programmers regardless of assigned domain, effectively making domains invisible. Programmers don’t have to code energy awareness. K2 works like any old Linux system with only a minor performance hit, satisfying all of the authors’ goals.

K2 was supported by a National Science Foundation (NSF) CAREER Award and is available for download from Work continues on K2 as the underlying SoC architectures keep advancing.

Reviewer:  Bayard Kohlhepp Review #: CR143657 (1510-0893)
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