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Computer Vision Metrics: Chapter Eight (Part F)

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For Part E of Chapter Eight, please click here.

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Fine-Grain Data Parallelism

Fine-grain parallelism refers to the data organization and the corresponding processor architectures exploiting parallelism, traditionally referred to as array processors or vector processors. Not all applications are data parallel. Deploying non-data-parallel code to run on a data-parallel machine is counterproductive; it’s better to use the CPU and straight-line code to start.

A data-parallel operation should exhibit common memory patterns, such as large arrays of regular data like lines of pixels or tiles of pixels, which are processed in the same way. Referring back to Figure 8-1, note that some algorithms operate on vectors of points, lines, and pixel regions. These data patterns and corresponding processing operations are inherently data-parallel. Examples of point operations are color corrections and data- type conversions, and examples of area operations are convolution and morphology. Some algorithms are straight-line code, with lots of branching and little parallelism. Fine-grained data parallelism is supported directly via SIMD and SIMT methods.

SIMD, SIMT, and SPMD Fundamentals

The supercomputers of yesterday are now equivalent to the GPUs and multi-core CPUs of today. The performance of SIMD, SIMT, and SPMD machines, and their parallel programming languages, is of great interest to the scientific community. It has been developed over decades, and many good resources are available that can be applied to inexpensive SOCs today; see the National Center for Supercomputing Applications[544] for a starting point.

SIMD instructions and multiple threads can be applied when fine-grained parallelism exists in the data layout in memory and the algorithm itself, such as with point, line, and area operations on vectors. Single Instruction Multiple Data (SIMD) instructions process several data items in a vector simultaneously. To exploit fine-grained parallelism at the SIMD level, both the computer language and the corresponding ALUs should provide direct support for a rich set of vector data types and vector instructions. Vector-oriented programming languages are required to exploit data-parallelism, as shown in Table 8-8; however, sometimes compiler switches are available to exploit SIMD. Note that languages like C++ do not directly support vector data types and vector instructions, while data-parallel...