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

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2007 power consumption contains many idle, low-power phases. In these phases, a small<br />

error in absolute terms yields a large percentage error. <strong>The</strong>re<strong>for</strong>e, error values are scaled<br />

<strong>by</strong> the magnitude of measured power sample compared to the maximum observed. For<br />

example, a 10% error on a 5W sample has half the impact of a 10% error on a 10W<br />

sample. For all subtests, the core-level versions of the predictors outper<strong>for</strong>med the<br />

aggregate versions. <strong>The</strong> best overall per<strong>for</strong>mance is 86% accuracy <strong>for</strong> the periodic core-<br />

level predictor compared to 83% <strong>for</strong> the core-level version of the last-value predictor.<br />

<strong>The</strong> benefit of core-level prediction of power is less pronounced than <strong>for</strong> prediction of<br />

activity level. This is due to the smaller dynamic range of power consumption compared<br />

to activity level. Though activity levels regularly vary from 0% to 100%, power levels<br />

remain in a much smaller range of approximately 25% to 75%.<br />

7.7 Summary<br />

This section presents the concept of core-level phase prediction and its application to<br />

dynamic power management. By observing changes in per<strong>for</strong>mance demand and power<br />

consumption at the core-level, it is possible to perceive predictable phase behavior.<br />

Prediction of phases allows power management to avoid over or under provisioning<br />

resources in response to workload changes. Using this concept the PPPP is developed. It<br />

is a simple, table-based prediction scheme <strong>for</strong> directing DVFS selection. It is applied to<br />

the SYSmark2007 benchmark suite and attain significant per<strong>for</strong>mance and power<br />

improvements. Compared to the reactive DVFS algorithm used <strong>by</strong> Windows Vista,<br />

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