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Energy characteristics of interactive systems

Fig. 1 shows the power consumption when the Qtopia [23] Calculator is used by a user on a Linux-based Sharp Zaurus SL-5500 PDA, to compute $(89\times56)\div45$. The power is sampled at a rate of 400 samples per second.
Figure 1: Power consumption of Sharp Zaurus while running Calculator.
\begin{figure}\centering\epsfig{file=calculator.eps,
height=3in}\vspace* {-7mm} \end{figure}

In Fig. 1, there are power valleys separated by nine major power peaks, which correspond to software responses to user tapping of GUI buttons. In the power valleys, the system waits for user input while the Linux kernel does maintenance jobs like handling timer interrupts and scheduling, which introduces small fluctuations and several minor spikes in the valley. Such power characteristics are typical of most interactive software usage.

To see how much time and energy the valleys take, we analyzed usage traces for two users of four commercial applications shipped with the PDA, as detailed in Section VII. The percentage of total time and energy the PDA spent waiting for user input is shown in Table 1. Clearly, over 90% of the time and energy was spent in waiting for user input. Moreover, most of the waiting periods are longer than 500ms. This demonstrates the vast opportunities available for power optimization of such interactive systems.

Table 1: Percentage of system time and energy spent waiting for user input
Benchmarks User Total time (s) Time(%) Energy(%)
Calculator 1 39.2 99.4 98.5
2 17.4 99.8 97.8
Filebrowser 1 187.5 99.1 97.6
2 106.3 98.7 96.4
Go 1 1,214.9 97.9 94.2
2 258.9 94.6 90.2
Solitaire 1 734.3 99.8 99.6
2 397.2 99.1 97.4


next up previous
Next: Power optimization for interactive Up: Background and Related Work Previous: Background and Related Work
Lin Zhong 2003-12-20