A computer uses instruction pipelining with P=4 stages named FD, DO, EX, WO. Each stage takes T seconds to perform its task. Suppose you have N=9 instructions in your program which has a branch from instruction 4 to 8. Draw a figure to show what
A computer system that utilizes instruction pipelining with P=4 stages, namely FD (Fetch and Decode), DO (Dispatch and Operand Fetch), EX (Execute), and WO (Writeback), can significantly improve the performance of program execution by overlapping the execution of multiple instructions. This overlapping is achieved by breaking down the execution of each instruction into smaller sequential stages and allowing different instructions to be processed at different stages simultaneously.
Let’s consider a program with N=9 instructions and a branch from instruction 4 to 8. To demonstrate how instruction pipelining works in this scenario, we can represent the progress of each instruction through the pipeline using a timeline figure. The horizontal axis of the timeline represents time, while the vertical axis represents the pipeline stages.
| FD | DO | EX | WO | FD | DO | EX | WO |
Instruction 1: | XXXX|
Instruction 2: | XXXX|
Instruction 3: | XXXX|
Branch from instruction 4 to 8:
Instruction 4: | XXXX|
Instruction 5: | XXXX|
Instruction 6: | XXXX|
Instruction 7: | XXXX|
Instruction 8: | XXXX|
Instruction 9: | XXXX|
In the timeline figure above, the vertical bars represent the different stages of the pipeline, and the X’s indicate the progress of each instruction through the pipeline stages.
Initially, instructions move from the Fetch and Decode (FD) stage to the Dispatch and Operand Fetch (DO) stage. After that, they move to the Execute (EX) stage and finally to the Writeback (WO) stage. Each stage takes T seconds to complete its task.
As the instructions progress through the pipeline, the pipeline stages become occupied by different instructions simultaneously. This overlapping execution allows the system to maximize the utilization of its resources and increase overall performance.
In the example shown above, the branch instruction at instruction 4 causes a change in the sequential order of instructions. The branch instruction redirects the execution flow to instruction 8, skipping instructions 5, 6, and 7. This demonstrates the flexibility of instruction pipelining to handle branching instructions and maintain efficient execution.
In conclusion, instruction pipelining is an effective method for improving performance in computer systems. By breaking down instructions into smaller stages and executing them in parallel, instruction pipelining maximizes resource utilization and enables efficient execution of programs.