Power Management

When does "race to idle" (finishing work fast and then sleeping deeply) tend to save energy?

  1. AWhen there is only dynamic power and no static power at all
  2. BWhen static power and the power of other components, such as memory, that stay active during work are large, so sleeping sooner shuts them all down
  3. CWhen entering sleep does not reduce power at all
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Answer: B. When static power and the power of other components, such as memory, that stay active during work are large, so sleeping sooner shuts them all down

Considering dynamic power alone, computing slowly at low voltage uses less energy. In reality, leakage and the power of memory, peripherals, the display and so on continue while the system is active. When these are large, finishing quickly at high performance and entering deep sleep, shutting everything down, uses less total energy. Which strategy wins depends on each device's power breakdown.

  • A. Then running slowly at low voltage is better.
  • B. Correct. Shortening active time pays off more.
  • C. If sleep saves nothing, sleeping early is pointless.
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More Power Management questions

  1. What is the role of a governor, such as a cpufreq governor, that sets CPU frequency in Linux and other OSes?
  2. Which describes CPU turbo operation (such as Turbo Boost)?
  3. Which describes thermal throttling?
  4. Some CPU power limits let the chip run above the long-term average limit (close to TDP) for short periods. Why does this work?
  5. What is the most suitable use of features such as Intel RAPL that let software measure CPU and memory power and set caps?