(c) Consider that an instruction pipeline has three stages namely instruction fetch and decode (FD), Operand Fetch (OF) and Instruction Execute and store results (ES). Draw an instruction pipeline diagram showing the execution of five sequential instructions using this pipeline. What are the problems with this instruction pipelining?

, , No Comments

 Instruction Pipeline Diagram:


Clock Cycle:      1       2       3       4       5       6       7       8


Instruction 1: | FD | OF | ES |                                          

Instruction 2:      | FD | OF | ES |                                   

Instruction 3:           | FD | OF | ES |                            

Instruction 4:                | FD | OF | ES |                       

Instruction 5:                     | FD | OF | ES |                  



In the above diagram:

- FD: Instruction Fetch and Decode stage

- OF: Operand Fetch stage

- ES: Instruction Execute and Store Results stage

Problems with Instruction Pipelining:

1. Pipeline Stall (Data Hazard): Data hazards may occur when an instruction depends on the result of a previous instruction still in the pipeline. In such cases, the pipeline may stall, leading to reduced throughput.

2. Control Hazard: Branch instructions may result in control hazards, causing a misprediction of branches and subsequent flushing of the pipeline. This can lead to inefficiencies in pipeline utilization.

3. Pipeline Flush: If an exception or error occurs in the pipeline, the entire pipeline may need to be flushed to maintain program correctness. This introduces delays and reduces the benefits of pipelining.

4. Resource Contention: Limited resources such as functional units or registers may cause contention, leading to pipeline stalls and reduced performance.

5. Pipeline Bubbles: Inefficient instruction scheduling or dependencies between instructions may create pipeline bubbles, where stages remain idle, reducing overall efficiency.

6. Dependency Handling: Dependencies between instructions, especially RAW (Read-After-Write) dependencies, require careful handling to avoid stalls or hazards.

7. Complexity: Implementing and managing an instruction pipeline introduces complexity in the design and may require additional circuitry for hazard detection, forwarding, and control.

8. Increased Latency: While pipelining improves throughput, it may increase the latency of individual instructions due to the pipeline stages, leading to longer execution times for certain instructions.

Addressing these issues requires careful design considerations, including techniques such as instruction reordering, speculation, forwarding, and out-of-order execution. Additionally, the use of advanced branch prediction mechanisms can mitigate control hazards and improve pipeline efficiency.

0 टिप्पणियाँ:

Post a Comment