Comment 15 for bug 177646

Yes. If you use p4_clockmod, you can alter the frequency of the processor. However, you cannot alter the voltage. As a result, you can reduce the power consumption of your processor by around a third only by making it take twice as long to do anything. This does not save you power overall.

C states allow the processor to unclock itself and save significant quantities of power by disabling unused portions of the CPU. They are automatically used on Linux, even on the Celeron. However, they can only be entered if the processor is entirely idle. If you use p4_clockmod then your processor will spend more of its time working and less time in the C states. As a result, it will consume more power than if you don't use p4_clockmod.

HMC8: Modern Intel processors only support reducing the core voltage (which can reduce power consumption) if they have "est" in their flags field. Otherwise, it's better to run at full speed in order to allow earlier entry to the C states.