Power Management

What is the idea behind the tickless kernel used in Linux and other OSes?

  1. AHiding the clock display to reduce screen power
  2. BWhen idle, the periodic timer tick interrupt is stopped so the CPU can sleep until the next work
  3. CRaising the timer tick interrupt to tens of thousands per second
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Answer: B. When idle, the periodic timer tick interrupt is stopped so the CPU can sleep until the next work

Traditional OSes used a timer tick interrupt, say 100 to 1000 times per second, for task switching and timekeeping, waking the CPU each time even with nothing to do. A tickless kernel stops the tick on idle CPUs and programs a timer only for the next time it actually needs to wake. The CPU can then sleep longer and deeper, reducing standby power.

  • A. It has nothing to do with the display.
  • B. Correct. It reduces standby power.
  • C. It reduces interrupts instead.
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More Power Management questions

  1. What is the Arm WFI (Wait For Interrupt) instruction used for?
  2. What is commonly used to wake a battery-powered device from sleep at a set time?
  3. If only the supply voltage is lowered by 10% (all else equal), by roughly what percentage does dynamic power fall?
  4. In the CMOS dynamic power formula P = αCV²f, what does α represent?
  5. What is the dynamic power of a circuit with activity factor α = 0.1, switched capacitance C = 1 nF, supply voltage V = 1 V and frequency f = 1 GHz?