Thread: Overclock the N900?
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Benson is offline Benson
2010-04-23 , 00:51
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#3252
Originally Posted by egoshin View Post
It is difficult to say. The total energy from battery definitely increases with higher frequency even you run with low voltage. And most of that energy dissipates on CPU.

Just to understand better that a small example. I ran a stock kernel and measured a current from battery under different frequencies. The 250MHz (playing MP3 music) takes only around 110mA but 600MHz (hard loop in shell) takes TEN times more - around 1400mA (screen is dark etc). But CPU VDD1 voltage still differs only 1.26 times (1.58 in square).

So, the biggest power consumption increase is in frequency increase.
Your data's not sufficient to show that. You're running two quite different workloads, and I suspect it's not clocking most of the time with the MP3 load. Now if you run the same loop with the frequency limited to 250 MHz, you'd have an accurate comparison, and I'd expect the power to scale something like V^2*F.

Assuming the V^2*F WAG is right, overclocking from 600 to 850 would be the same power if you can reduce voltage from 1.35V to 1.13V, and -- assuming your workload involves doing fixed tasks followed by idling (instead of runaway loops, games that can't keep framerate up on either setting, etc.) -- the overclocked option will finish sooner and run cooler overall. So I'd guess that esthrel's comparison of 850MHz@1.2V is not harder on the CPU than stock settings for typical usage, but you're right, it is hard to say.
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