An analysis of the effectiveness of energy management on modern computer processors

Managing energy consumption has become a critical issue for computer system designers. End-users are forced to charge battery-powered devices on a daily basis because battery technology has not kept pace with the demands of the power-hungry processors and peripherals used in today’s mobile devices. Thousands of servers in data-centres also use power-hungry processors which result in huge costs for power and cooling. This is impacting our environment by accelerating global climate-change. To help mitigate these problems, processor manufacturers have implemented various powermanagement mechanisms, including dynamic voltage and frequency scaling (DVFS) and low-power idle modes, to reduce and manage the power consumption of their processors. These mechanisms are controlled by the operating system (OS) and in the past, their use could result in significant improvements in energy efficiency. However, changes in semiconductor technology are altering the effectiveness of these mechanisms. This thesis shows that on recent platforms, using DVFS results in only marginal reductions in systemlevel energy consumption for realistic workloads such as MPEG video playback. However, we find that the system-level energy consumption of lightly loaded web-servers can be reduced without impacting throughput or response latency. This results in an improvement in energy efficiency. However, several trends exist which are leading to diminishing returns from traditional powermanagement mechanisms. We analyse these trends to determine their impact on the effectiveness of the energy-management techniques used in systems today, and look into the future to see what might help to reduce the energy consumption of the computer systems of tomorrow.

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