14.1.6. Heterogeneous multi-processing

The term Heterogeneous multi-processing (HMP) finds application in many different contexts. It is often conflated with AMP to describe systems that are composed of different types of processors, such as a multi-core ARM applications processor and an application-specific processor (such as a baseband controller chip or an audio codec chip).

ARM uses HMP to mean a system composed of clusters of application processors that are 100% identical in their instruction set architecture but very different in their microarchitecture. All the processors are fully cache coherent and a part of the same coherency domain.

This is best explained using the ARM implementation of HMP technology known as big.LITTLE. In a big.LITTLE system, the energy efficient LITTLE cores are coherently coupled with high performance big cores to form a system that can accomplish both high intensity and low intensity tasks in the most energy efficient manner.

Figure 14.1. A typical big.LITTLE system

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The central principle of big.LITTLE is that application software can run unmodified on either type of processor. For a detailed overview of big.LITTLE technology, and its software execution models see Chapter 16.

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