Oct 29, 2014

What is a big.LITTLE processor and what are its advantages over other CPUs?

ARM has released what it calls a “big.LITTLE” processor. Is this really a new architecture, and if so, what are it’s advantages, if any, over conventional CPUs?

Modern processors have diverse workloads (e.g. multimedia, encryption), optimization objectives (e.g. performance, power, fairness), usage pattern (high usage, inactivity) etc. Hence, even a highly-optimized "monolithic" core cannot simultaneously meet these diverse and often conflicting requirements. For this reason, asymmetric multicores have been proposed which have different cores (e.g. big and LITTLE), each optimized for a particular usage/workload/objective.
For detailed answer, see my survey which reviews ~125 papers on big.little style asymmetric multicores: https://www.academia.edu/18301534/A_Survey_Of_Techniques_for_Architecting_and_Managing_Asymmetric_Multicore_Processors

"ARM big.LITTLE is a heterogeneous computing architecture developed by ARM Holdings, coupling (relatively) slower, low-power processor cores with (relatively) more powerful and power-hungry ones. The intention is to create a multi-core processor that can adjust better to dynamic computing needs and use less power than clock scaling alone.

In October 2011, big.LITTLE was announced along with the Cortex-A7, which was designed to be architecturally compatible with the Cortex-A15.[1] In October 2012 ARM announced the Cortex-A53 and Cortex-A57 (ARMv8-A) cores, which are also compatible with each other to allow their use in a big.LITTLE chip.[2] ARM later announced the Cortex-A12 at Computex 2013 followed by the Cortex-A17 in February 2014, both can also be paired in a big.LITTLE configuration with the Cortex-A7.[3][4]"
Basically, the little chip does the everyday work and the big one does the power intensive work, so you get better battery life.

“The idea of big.LITTLE is to pair a tiny and ultra-low power ARM Cortex A7 core to a fast and modern Cortex A15 core so that when a menial task is required, the A7 can take care of it without requiring the muscles (and energy) of the A15 core. Both cores are architecturally compatible and can run the same software. Tasks can be migrated on the fly from one to the other, which is the beauty of the system. The Cortex A7 core at peak utilization still draws less power than the A15 core at its lowest operating point but, it can still get a number of small tasks done.”
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