Frequency vs. power consumption
Posted Feb 26, 2012 5:03 UTC (Sun) by jzbiciak
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Parent article: The Linaro Connect scheduler minisummit
Because CPU power consumption often rises as the square of the core clock frequency, you typically get the best battery life by running the CPU at the lowest frequency that gets the work done in time.
If I'm not mistaken, dynamic power is linearly proportional to clock speed, holding all other things constant. (Leakage power remains constant.) Both dynamic and leakage power, though, tend to be proportional to the square of voltage. (Power is V2 / R.) Now, if you need to increase voltage to get to a higher clock speed, then yes, the statement is true to an extent, but not all systems adjust voltage with clock frequency.
BTW, there's another reason running the CPU at a higher clock doesn't always help. If you have a memory-bound workload, such that you spend most of your time in cache miss cycles, you're just going to burn a lot of clock power running the CPU faster, without speeding up the workload appreciably. This is mentioned in the article as a possible reason to move a task from the A15 to the A7, but it's also just a more general argument for setting the "right" clock rate based on what you know of the task.
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