On 10/30/07, Dana H. Myers <Dana.Myers at sun.com> wrote: > > I would agree with Aubrey that T-states don't save power if by "save" we > > mean that we can do the same amount of work at the same amount of time > > while consuming less energy. > I don't think P-states meet this definition of saving power, either, do > they?
Actually, I think P-states can be (at least theoretically) used in such a way that this definition is met. In an ideal environment where we know precisely what are the requirements in terms of CPU cycles of a given workload, we can afford putting CPU into lower FID/VID without loosing performance and increasing run times while saving power. Attempting to do the same thing with T-states will not save any power because we're going to stay in C1 with or without T-states. Also, just spending C1 time in lowest P-state alone can save power on AMD CPUs which don't automatically drop frequencies/voltages upon entering C1 (which is what C1E on Intel CPUs is for). - Andrei
