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Copyright by William Lloyd Bircher 2010 - The Laboratory for ...

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Chapter 1 Introduction<br />

Computing systems have a wide range of design objectives. Metrics such as<br />

per<strong>for</strong>mance, power and cost must be carefully managed in order to meet these<br />

objectives. While some parameters are fixed at design time, others such as per<strong>for</strong>mance<br />

and power consumption may be dynamically adjusted at run-time. This allows a system<br />

to be optimal across a wider range of workloads and usage scenarios. This dynamic<br />

optimization, commonly known as dynamic power management, allows per<strong>for</strong>mance to<br />

be exchanged <strong>for</strong> power savings. <strong>The</strong> amount of savings is constrained <strong>by</strong> the system<br />

objectives. For example, systems with quality of service (QoS) requirements can allow<br />

power and per<strong>for</strong>mance to be reduced only as long as the service demands are met.<br />

Mobile systems powered <strong>by</strong> batteries must be optimized to deliver the highest<br />

per<strong>for</strong>mance/Watt in order to maximize usage time. Compute-cluster per<strong>for</strong>mance<br />

capacity must be modulated to match demand so that per<strong>for</strong>mance/cost is maximized.<br />

Adaptation within these scenarios requires accurate, run-time measurement of<br />

per<strong>for</strong>mance and power consumption. Run-time measurement of power and per<strong>for</strong>mance<br />

allow tradeoffs to be made dynamically in response to program and usage patterns.<br />

1.1 Attributing Power in Multi-Core Systems<br />

Multi-core and multi-threaded systems present significant challenges to power<br />

measurement. While per<strong>for</strong>mance is readily measurable at the core and program-level,<br />

1

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