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Okay, I'm looking for hard evidence to settle an argument.

From a developers perspective, the argument of CPU usage and battery life comes into play often.

If a CPU is throttled to use 10% of its capacity, thus taking 10x as long to complete a process,
Is it not just as efficient for the CPU to be set to 100% and have it complete the process sooner? And then be idle

I ask this from a battery perspective. We want to know if lowering CPU freq can actually allow you to preform more processing tasks? OR if it just allows you to do more, slower, but over more time.

I've re-worded the example to better explain what I mean.

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A program should not throttle its CPU usage when it has work to do. If that were the right thing to do, we'd all just buy CPUs that were one tenth as fast. –  David Schwartz Jun 27 '12 at 19:09
    
hmm, you want somebody to have tested it.. I hope somebody finds something. You could use an Electricity Usage Monitor / Power meter/metre plug, energy metre/meter , whatever thing. upload.ecvv.com/upload/Product/200801/… That can tell you watts,volts,amps. What program might you use to throttle it? Of course, ideally you want somebody to have already done the tests! Also it's not clear whether you mean lowering cpu freq, or throttling programs to use less cpu. Maybe you want to know for both. –  barlop Jun 27 '12 at 19:25
    
@DavidSchwartz what if you had no access to a plug and wanted to save power? Maybe some do lower cpu frequency to e.g. make the laptop use less heat. like some undervolt. And certainly sometimes a program uses 100% of cpu and holds up a machine and one might want it to use less cpu. (though that may not be so relevant now with multiple cores). re heat, there was a program called cpuidle cpuidle.de which maybe sends the cpu HALT instructions(if there is such a thing) at certain times. –  barlop Jun 27 '12 at 19:31
    
@barlop: We pay top dollar for fast CPUs so that when there is work to do, it gets done as quickly as possible. We drop the CPU speed and voltage to avoid wasting power and causing excess heat when there's less work to do. –  David Schwartz Jun 27 '12 at 19:38
    
@DavidSchwartz And what if one is in a weird environment where there's lots of work to do and not much power available? then what do we do? For a car, apparently mpgforspeed.com optimal MPG(miles per gallon) is at 55-60MPH and fuel efficiency drops after that. He wants fuel or in this case, wattage/power efficiency or energy use efficiency. –  barlop Jun 27 '12 at 19:43

1 Answer 1

up vote 2 down vote accepted

There is no single answer to this.

CPUs use more energy per instruction when operating at higher frequency and voltage. And idle usage is not zero. This favors doing the processing at undervolt/underfrequency.

But other system components also consume power (at a fairly steady rate, except spinning disks which tend to consume much more power when work is being done, regardless of hos fast). This favors doing the work at high CPU frequency, before the other components consume all the battery.

Which effect is greater is highly system specific and may even depend on your actual workload.

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