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

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these environments will take account of power consumed <strong>by</strong> each process [Mc04]. This<br />

is particularly challenging in virtual machine environments in which multiple customers<br />

could be simultaneously running applications on a single physical processor. For this<br />

reason, process-level power accounting is essential.<br />

Given that the Pentium IV can fetch three instructions/cycle, the model predicts range of<br />

power consumption from 9.25 Watts to 48.6 Watts. <strong>The</strong> <strong>for</strong>m of the model is given in<br />

Equation 5.1.<br />

Watts<br />

NumCPUs<br />

∑<br />

i =<br />

200<br />

150<br />

100<br />

1<br />

9.<br />

25<br />

+<br />

( 35.<br />

7<br />

−<br />

9.<br />

25)<br />

× PercentActive<br />

Figure 5.2 Processor Power Model – gcc<br />

72<br />

i<br />

+<br />

FetchedUopsi<br />

4.<br />

31×<br />

Cycle<br />

100%<br />

A trace of the total measured and modeled power <strong>for</strong> the four processors is given in<br />

Figure 5.2. <strong>The</strong> workload used in the trace is eight threads of gcc, started at 30s intervals.<br />

Average error is found to be 3.1%. Note that unlike the memory bound workloads that<br />

saturate at eight threads, the cpu-bound gcc saturates after only 4 simultaneous threads.<br />

50%<br />

50<br />

Measured<br />

Modeled<br />

-50%<br />

0<br />

Error<br />

-100%<br />

0 100 200 300 400<br />

Seconds<br />

0%<br />

Error (%)<br />

(5.1)

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