[miratrix]

Leakage power is actually very significant part of the total power usage [1] and one of the bigger reasons why Intel developed the tri-gate technology [2].

Active power is the one that's related to the frequency (P ~= CV^2f). Leakage power will "leak" even if the transistor is not switching.

1. http://www.eetimes.com/electronics-news/4215605/Leakage-powe... 2. http://realworldtech.com/page.cfm?ArticleID=RWT050511195446

[microarchitect]

Not sure what you mean by significant, but typical leakage power numbers are something like 15-30% of total power.

Maybe you're referring to some papers that used to come out a few years ago which suggested that leakage power will dominate total power. As I said above, this is unlikely to happen. It doesn't make sense to operate at a combination of supply voltage (Vdd) and threshold voltage (Vt) where leakage dominates total power. I think these papers misunderstood the fact that threshold voltage and hence leakage itself is a knob that the device manufacturing folks can control.

Active power is the one that's related to the frequency (P ~= CV^2f). Leakage power will "leak" even if the transistor is not switching.

If you're implying that leakage power doesn't affect frequency, you are wrong. Transistor speed depends on the gate overdrive which, for modern velocity-saturated devices is proportional to Vdd-Vt. Leakage power itself is proportional to exp(-Vt). There is a clear trade-off here between how fast you run your chip and how much it will leak.

[miratrix]

The papers I've seen point to values larger than 15~30% - I've seen ~50% cited for geometries as large as 65nm, only to get worse as we go to even smaller feature sizes. [1]

Threshold voltage is not really an effective knob, unless you assume that the feature size to be a knob and go against Moore's law, or that brand new, once in 10-years process innovation is a knob that designers can pick out of a hat. I don't think anyone's clamoring for return to 130nm parts on a smartphone. At each new process node, you're going to lose out on the amount of control you'll have over Vth.

This is basically what Intel did with the tri-gate transistors which gives them longer lease on life until they bump against subthreshold leakage. TSMC is on their first generation high-k metal gates, and still a process node or two away before jumping over to the tri-gate party.

1. http://www.eetimes.com/design/eda-design/4211228/Overcoming-...