The disparity between memory and CPU have been ameliorated by the introduction of Network-on-Chip-based Chip-Multiprocessors (NoC-based CMPS). However, power consumption continues to be an aggressive stumbling block halting the progress of technology. Miniaturized transistors invoke many-core integration at the cost of high power consumption caused by the components in NoC-based CMPs; particularly caches and routers. If NoC-based CMPs are to be standardised as the future of technology design, it is imperative that the power demands of its components are optimized. Much research effort has been put into finding techniques that can improve the power efficiency for both cache and router architectures. This work presents a survey of power-saving techniques for efficient NoC designs with a focus on the cache and router components, such as the buffer and crossbar. Nonetheless, the aim of this work is to compile a quick reference guide of power-saving techniques for engineers and researchers.

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Power consumption in Complementary Metal Oxide Semiconductor (CMOS) technology has escalated to a point that only a fractional part of many-core chips can be powered-on at a time. Fortunately, this fraction can be increased at the expense of performance through the dark-silicon solution. However, with manycore integration set to be heading towards its thousands, power consumption and temperature increases per time, meaning the number of active nodes must be reduced drastically. Therefore, optimized techniques are demanded for continuous advancement in technology. Existing efforts try to overcome this challenge by activating nodes from different parts of the chip at the expense of communication latency. Other efforts on the other hand employ run-time power management techniques to manage the power performance of the cores trading-off performance for power. We found out that, for a significant amount of power to saved and high temperature to be avoided, focus should be on reducing the power consumption of all the on-chip components. Especially, the memory hierarchy and the interconnect. Power consumption can be minimized by, reducing the size of high leakage power dissipating elements, turning-off idle resources and integrating power saving materials.

The end of Dennard scaling has shifted the focus of performance enhancement in technology to power budgeting techniques, specifically in the nano-meter domain because, leakage power depletes the total chip budget. Therefore, to meet the power budget, the number of resources per die could be limited. With this emerging factor, power consumption of on-chip components is detrimental to the future of transistor scaling. Fortunately, earlier research has identified the Last Level Cache (LLC) as one of the major power consuming element. Consequently, there have been several efforts towards reducing power consumption in LLCs. This paper presents a survey of recent contribution towards reducing power consumption in the LLC.