The Samsung Exynos 5 uses two A15 cores which are pretty power hungry.
In the A7/A15 big.little approach, the A7 does most of the work and the A15 just powers up a minority of the time to blast through intense jobs. That should cut power by 150% or more, ARM estimates.
Now I wonder, will Intel adopt this concept in mobile?
There have been many research projects that have looked at combining Atom and "big cores" e.g. Ivy Bridge and Haswell as well as ARM processors to handle low-level OS functions and some applications while the bigger cores are sleeping. In fact, I think Dell had a laptop that had both "ARM & Intel Inside" to do roughly the same thing.
The A15 is a hot, complex chip that's not particularly performant for the power nor does it yield particularly well. That A7 companion chip and the entire Big.Little concept is a tacit admission of that regrettable reality.
@ Rick, a Dual core A15 @ 2GHz in our lab is consuming 4W. Mind you, this is just the CPU Cores. When we add the Graphics, Video and IOs, you are looking at around 6-7W. ARM is in big trouble. This big.Little is just a hog-wash. Unless we see this from a 3rd party, I cant believe 50% improvement. ARM CEO can say Power this and power that, but his ARM Cores are getting worse by day.