Difference between Fine-Grained and Coarse-Grained SIMD Architecture

Differences Computer Architecture Data Structure

SIMD stands for Single Instruction Multiple Data. A type of computer architecture in which a single instruction can be executed on multiple pieces of data in parallel is referred to as a SIMD (Single Instruction Multiple Data) architecture.

Therefore, SIMD architecture is primarily used in parallel processing application where large amounts of data required to be processed at the same time.

In the case of SIMD, a single instruction is executed on a group of data that are stored in contiguous memory locations. SIMD architecture is used in a variety of applications audio and video processing, simulations, 3D graphics processing, data compression, data encryption, etc. Examples of SIMD architectures include AVX, MMX, SSE, etc.

Depending on the level of granularity of data processing, SIMD architectures can be of two types namely, Fine-Grained SIMD Architecture and Coarse-Grained SIMD Architecture. The main difference between fine-grained SIMD architecture and coarse-grained SIMD architecture is that the fine-grained SIMD architecture processes individual data elements simultaneously by using a single instruction, while the coarse-grained SIMD architecture processes a larger group of data elements simultaneously by using a single instruction.

In this article, we will discuss the important differences between fine-grained and coarse-grained SIMD architectures. But before discussing the differences, let us first have a look into their basics.

What is Fine-Grained SIMD Architecture?

The type of SIMD (Single Instruction Multiple Data) computer architecture in which individual data elements are processed at the same time using a single instruction is referred to as fine-grained SIMD architecture.

Therefore, in the fine-grained SIMD architecture, a single instruction is executed on a small group of data elements which are stored in contiguous memory locations. Fine-grained SIMD architecture provides a high degree of parallel processing, as a single-instruction can process multiple data elements at the same time. Consequently, it improves the performance of the system. On the other side, fine-grained SIMD architecture could be less efficient for executing tasks that involve simultaneous processing of a group of large data elements.

Some common examples of fine-grained SIMD architecture include MMS, AVX, and SSE that are extensions of the 32-bit architecture.

What is Coarse-Grained SIMD Architecture?

A type of SIMD (Single Instruction Multiple Data) architecture that can process larger groups of data elements simultaneously using a single instruction is referred to as a coarse-grained SIMD architecture.

The implementation of coarse-grained SIMD architecture requires array processors to process data in large arrays or blocks. Therefore, in the case of coarse-grained SIMD architecture, a single instruction is executed on a large group of data elements that are stored in a multidimensional array.

Coarse-grained SIMD architecture enables to process a large amount of data more efficiently. This type of SIMD architecture is commonly employed in applications like scientific simulation, database queries, etc.

Some common examples of coarse-grained SIMD architecture are Cray XD1, Mas Par MP-1 and MP-2, Connection Machine, etc.

After getting a brief overview of fine-grained and coarse-grained SIMD architectures individually, let us now study their important differences.

Differences between Fine-Grained and Coarse-Grained SIMD Architectures

The following table highlights all the major differences between fine-grained and coarse grained SIMD architecture:

S.No.	Fine-Grained SIMD Architecture	Coarse-Grained SIMD Architecture
1.	A type of SIMD (Single Instruction Multiple Data) architecture in which a single instruction is executed on individual data elements simultaneously is termed as a fine-grained SIMD architecture.	A type of SIMD architecture in which a single instruction is executed on a large group of data elements simultaneously is termed as a coarse-grained SIMD architecture.
2.	Fine-grained SIMD architecture is suitable for processing small blocks of data.	Coarse-grained SIMD architecture is suitable for processing large blocks of data.
3.	Fine-grained SIMD architecture requires less computation time.	Coarse-grained SIMD architecture requires comparatively more computation time.
4.	In the case of fine-grained SIMD architecture, programs are split into a large number of small units.	In the case of coarse-grained SIMD architecture, programs are split into a small number of large units.
5.	The aligned data is required in the case of fine-grained SIMD architecture.	The coarse-grained SIMD architecture can process unaligned data efficiently.
6.	Fine-grained SIMD architecture offers a high degree of parallelism.	Coarse-grained SIMD architecture offers lower degree of parallelism.
7.	Fine-grained SIMD architecture is more efficient for tasks that involve processing of small amounts of data.	Coarse-grained SIMD architecture is more efficient for tasks, involving processing of huge amount of data.
8.	In the case of fine-grained SIMD architecture, the grain size is more than 1000 instructions.	In the case of coarse-grained SIMD architecture, the grain size ranges from 2 to 500 instructions.
9.	In the fine-grained SIMD architecture, there are two types of parallelism that can be obtained namely, Instruction Level Parallelism and Loop Level Parallelism.	In the coarse-grained SIMD architecture, the types of parallelism obtained are: Sub-Program Parallelism and Program Level Parallelism.
10.	The parallelism in the fine-grained SIMD architecture can be detected using a compiler.	The parallelism in the coarse-grained SIMD architecture cannot be detected through complier.
11.	There is a proper load balancing in the case of fine-grained SIMD architecture.	Coarse-grained SIMD architecture has improper load balancing.
12.	Fine-grained SIMD architecture is more expensive.	Coarse-grained SIMD architecture is less costly.
13.	Fine-grained SIMD architecture offers high speed processing for small data blocks.	Coarse-grained SIMD architecture provides high speed processing for large data blocks.
14.	The hardware implementation of fine-grained SIMD architecture requires vector processors.	The hardware implementation of coarse-grained SIMD architecture requires array processors.
15.	In the case of fine-grained SIMD architecture, specialized instruction sets are used.	In the case of coarse-grained SIMD architecture, generic instruction sets are used.
16.	The code complexity in fine-grained SIMD architecture is higher.	The code complexity in the coarse-grained SIMD architecture is comparatively lower.
17.	Fine-grained SIMD architecture is suitable for tasks like single processing, image processing, matrix multiplication, and many other where high-degree of parallelism is required.	Coarse-grained SIMD architecture is suitable for applications like scientific simulation, data queries, and many other where processing of large amount of data is required.

Conclusion

Both type of SIMD architectures offers different levels of granularity in data processing. The most significant difference between fine-grained SIMD architecture and coarse-grained SIMD architecture is that the fine-grained SIMD architecture is one which is implemented using vector processors and processes data in small vectors, whereas the coarse-grained SIMD architecture is one which is implemented using array processors and processes data in large arrays.

Manish Kumar Saini

Updated on: 16-May-2023

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