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I searched high and low for what “Intel P state” is and what it does. I found out that it has to do with performance and power consumption. I learned that if you build it in the kernel, it'll becomes the default scaling driver for Intel CPUs.

But What I want to know is, what does it do?

Does it reduce CPU functionality and power in favour of reducing power consumption, or does it manage and balance the CPU state, i.e if CPU is under heavy load and compiling something it boosts the CPU frequency to compensate and it reduces it when it is idle?

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P states on x86 processors are levels of voltage scaling. When a processor runs at higher voltage, it can run faster, but it also uses more energy and heats more. The P state numbering is standardized: 0 to 15, from fastest to slowest.

It is up to the kernel to decide when to switch between P states. The kernel will switch to a lower-numbered (faster, hotter) state when it detects a heavy workload (the CPU is never idle), and switch back to a higher-numbered (slower, cooler) state when it detects that the CPU has spare time.

The P state driver is the part of the kernel that takes the decision to switch between P states.

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  • An additional note: the P states driver operates on the "race to idle" paradigm. The end result should actually be higher performance and energy-efficiency than older drivers can offer. – HalosGhost Oct 10 '14 at 17:27

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