操作系统导论习题解答（4. Processes）

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本文介绍了一个名为process-run.py的Python程序，该程序能够模拟进程运行时的状态变化，包括使用CPU执行指令和进行I/O操作。通过不同的场景设置，可以观察到进程在等待I/O完成或被调度执行时的行为差异。

Homework (Simulation)

This program, process-run.py, allows you to see how process states change as programs run and either use the CPU (e.g., perform an add instruction) or do I/O (e.g., send a request to a disk and wait for it to complete). See the README for details.

Target

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Introduction

type python process-run.py -h in the command, you should see:

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Question & Answer

1

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The CPU utilization is 100%.

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2

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It takes 10 clock ticks to complete both processes.

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First, process 0 was run, it took 4 clock ticks. Then process 1 issued an I/0 request, the CPU received and blocked process 1, it took 1 clock tick. Next the I/O took 4 clock ticks, and finally the CPU unblocked the process 1, process 1 was done, it took 1 clock tick.

3

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Process 0 issued an I/O request, the CPU blocked it and started I/O operations, it took 1 clock tick. When I/Os were running, process 1 issued the CPU request, after 4 clock ticks, I/Os and CPU finished. It takes a total of 6 clock ticks.

4

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When process 0 is doing I/0, the system will not switch to process 1, instead waiting until the process 0 is completely finished.

5

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It is the same as question 3.

6

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The system resources are not being effectively utilized.

7

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The difference between the two is whether the CPU accepts the next I/O request or runs the process instruction after the I/O operation is executed. Since the default mode SWITCH_ON_IO is adopted, the CPU executes instructions and I/O operations are performed simultaneously, so IO_RUN_IMMEDIATE is 1 clock tick faster.