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

suboptimal from a power and performance perspective. Though the CPU is capable of
drastically reducing idle power by operating at less than maximum frequency, it
frequently does not. On average 41% of idle time is spent at a higher than necessary
frequency and voltage. Similarly, performance is reduced by operating at less than the
maximum frequency for 70% of the time. This can greatly impact performance due to
the large increases in runtime that can eliminate energy efficiency gains from reduced
voltage and frequency.
To improve performance and efficiency, adaptation must be performed with an accurate
estimate of future demand. This prevents costly adaptations from being applied when
program phase are too short to amortize the performance and energy cost of adaptation.
To this end a predictive power manager is proposed.
Table 1.1 Windows Vista Reactive DVFS
E-Learning Productivity Video Creation 3D
2.4GHz - Active 4.6% 2.4% 5.3% 15.0%
2.4GHz - Idle 17.4% 9.6% 12.4% 17.0%
1.6GHz - Active 1.4% 0.8% 3.2% 5.1%
1.6GHz - Idle 9.4% 6.2% 9.6% 6.7%
1.2GHz - Active 1.2% 1.2% 4.8% 3.1%
1.2GHz - Idle 9.8% 9.7% 13.8% 9.4%
0.8GHz - Active 4.5% 4.7% 4.8% 6.9%
0.8GHz - Idle 51.8% 65.3% 46.1% 36.7%
Active Frequency 1.56 GHz 1.34 GHz 1.51 GHz 1.77 GHz
Idle Frequency 1.24 GHz 1.07 GHz 1.20 GHz 1.32 GHz
5