Energy-efficient does not mean low power. It means a better quotient of MIPS or GFLOPS per power unit used. Those numbers are published if the processors in question ran LINPACK or for I/O, a similar test.
The A57 is supposed to deliver 3x the performance of a15. Of course that means it would still need more cores than Xeon Phi. Interconnecting the cores also takes energy. I think it remains to be seen which is better in terms of performance/W.
As we unveil EE Times’ 2015 Silicon 60 list, journalist & Silicon 60 researcher Peter Clarke hosts a conversation on startups in the electronics industry. Panelists Dan Armbrust (investment firm Silicon Catalyst), Andrew Kau (venture capital firm Walden International), and Stan Boland (successful serial entrepreneur, former CEO of Neul, Icera) join in the live debate.