Pipelining

In computer science, pipelining is a technique used to improve the speed of processes by overlapping the execution of multiple steps in a system, often within a CPU or in parallel computing. The term is most commonly associated with CPU instruction pipelines, but it can also apply to other areas, such as network data processing or graphics rendering.

Key concepts

Instruction Pipeline (in CPUs)

Modern processors divide the execution of a machine instruction into several stages such as fetching the instruction, decoding it, executing it, and writing the result back to memory.
By pipelining, the CPU can work on multiple instructions simultaneously, with each stage handling a different part of an instruction at the same time, leading to improved throughput.

Stages of a Typical Instruction Pipeline

Fetch (F): Retrieve the instruction from memory.
Decode (D): Interpret the instruction and determine the required actions.
Execute (E): Perform the operation (e.g., arithmetic, memory access).
Memory Access (M): Load or store data if needed.
Write-back (W): Store the result in the appropriate location (e.g., register).

Hazards

Data hazards: Occur when instructions depend on the results of previous ones.
Control hazards: Occur due to branching and jumping in the program.
Structural hazards: Happen when multiple instructions require the same resources at the same time.

Parallelism

Pipelining exploits instruction-level parallelism by executing different parts of multiple instructions in parallel, as long as those instructions are independent of each other.

Other types

Pipeline in Data Processing: Used to process streams of data where each step in the pipeline performs a part of the task (e.g., stages in data packet processing in networks).
Graphics Pipeline: In graphics rendering, different stages like vertex processing, pixel shading, and rasterization are performed in a pipeline to render images efficiently.

Pipelining is a basic concept for improving system performance by breaking down processes into smaller, sequential steps that can be executed in parallel or with overlap.