Pipelining in COA

Pipelining is a method where a step-by-step process is split into smaller parts. Each part is handled in its dedicated section

that works simultaneously with other sections.

Imagine a pipeline as a set of processing stages where binary information moves through.

Each stage does part of the job based on how the task is divided. The outcome from each stage is sent to the next

one in the pipeline. The ultimate result is achieved after the data has gone through all the stages.

figure: Four-segment pipeline

Example:                      Ai*Bi+Ci   for i = 1, 2, 3, ... ,7

R 1 <——–  Ai, R2 +- Bi                              Input Ai and Bi
R3 <——— Rl*R2,   R4<—–Ci                    Multiply and input Ci
R5 <——–  R3 + R4                                     Add c; to product

Types of Pipeline:

There are two areas of computer design where the pipeline organization is applicable.

An arithmetic pipeline divides an arithmetic operation into suboperations for execution in the pipeline segments.

An instruction pipeline operates on a stream of instructions by overlapping the fetch, decode, and execute
phases of the instruction cycle.

Advantages and Disadvantages of pipelining:

Advantages:

1. Increased Throughput: Pipelining allows multiple instructions to be processed simultaneously, increasing the overall throughput of the processor. This results in higher performance and faster execution of programs.
2. Better Resource Utilization: By dividing the execution of instructions into stages, pipelining allows for better utilization of hardware resources. Each stage of the pipeline can be dedicated to a specific task, enabling efficient use of functional units within the processor.
3. Reduced Cycle Time: Since multiple instructions are overlapped in the pipeline, the cycle time for executing individual instructions is reduced. This leads to improved responsiveness and faster program execution.
4. Improved Instruction-Level Parallelism: Pipelining exploits instruction-level parallelism by allowing multiple instructions to be in different stages of execution simultaneously. This enables more efficient use of the processor’s resources and enhances performance.
5. Scalability: Pipelining is a scalable technique that can be applied to processors with varying degrees of complexity. It can be implemented in both simple and complex architectures, making it suitable for a wide range of computing systems.

Disadvantages:

1. Pipeline Hazards: Pipelining introduces various hazards, such as data hazards, control hazards, and structural hazards, which can impact performance. Resolving these hazards requires additional hardware logic and may result in pipeline stalls or delays.
2. Increased Complexity: Implementing a pipelined processor requires additional hardware complexity to manage the pipeline stages, handle hazards, and ensure correct instruction execution. This complexity can increase design and verification efforts and may result in higher manufacturing costs.
3. Pipeline Bubbles: Pipeline bubbles occur when the pipeline must be stalled or flushed due to hazards or branch mispredictions. These bubbles reduce the efficiency of the pipeline and can result in wasted clock cycles, affecting overall performance.
4. Limited Performance Gains: While pipelining can significantly improve throughput and performance, the extent of performance gains may be limited by factors such as the depth of the pipeline, the frequency of hazards, and the nature of the workload. In some cases, the overhead of pipelining may outweigh the performance benefits.
5. Sensitivity to Workload: The effectiveness of pipelining depends on the characteristics of the workload being executed. Workloads with frequent dependencies or unpredictable control flow may not fully exploit the benefits of pipelining, leading to suboptimal performance.