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79 changes: 79 additions & 0 deletions Chapter 4/README.md
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# The Abstraction: The Process

## 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 addin struction) or do I/O (e.g., send a request to a disk and wait for it to complete). See the README for details.

### Questions

1. **Run `process-run.py` with the following flags: `-l 5:100,5:100`. What should the CPU utilization be (e.g., the percent of time the CPU is in use?) Why do you know this? Use the `-c` and `-p` flags tosee if you were right.**

100%, because there is no IO process.
<br/>

2. **Now run with these flags: `./process-run.py -l 4:100,1:0`.These flags specify one process with 4 instructions (all to use the CPU), and one that simply issues an I/O and waits for it to be done.How long does it take to complete both processes? Use `-c` and `-p` to find out if you were right.**

4(process 0) + 5(process 1 IO) + 1 = 10

```
$ ./process-run.py -l 4:100,1:0 -cp
Time PID: 0 PID: 1 CPU IOs
1 RUN:cpu READY 1
2 RUN:cpu READY 1
3 RUN:cpu READY 1
4 RUN:cpu READY 1
5 DONE RUN:io 1
6 DONE WAITING 1
7 DONE WAITING 1
8 DONE WAITING 1
9 DONE WAITING 1
10* DONE DONE

Stats: Total Time 10
Stats: CPU Busy 5 (50.00%)
Stats: IO Busy 4 (40.00%)
```
<br/>

3. **Switch the order of the processes: `-l 1:0,4:100`. What happens now? Does switching the order matter? Why? (As always, use `-c` and `-p` to see if you were right)**

Process 1 runs when process 0 is waiting for IO completes.

```
$ ./process-run.py -l 1:0,4:100 -c -p
Time PID: 0 PID: 1 CPU IOs
1 RUN:io READY 1
2 WAITING RUN:cpu 1 1
3 WAITING RUN:cpu 1 1
4 WAITING RUN:cpu 1 1
5 WAITING RUN:cpu 1 1
6* DONE DONE

Stats: Total Time 6
Stats: CPU Busy 5 (83.33%)
Stats: IO Busy 4 (66.67%)
```
<br/>

4. **We’ll now explore some of the other flags. One important flag is `-S`, which determines how the system reacts when a process issues an I/O. With the flag set to `SWITCH_ON_END`, the systemwill NOT switch to another process while one is doing I/O, instead waiting until the process is completely finished. What happens when you run the following two processes (`-l 1:0,4:100 -c -S SWITCH_ON_END`), one doing I/O and the other doing CPU work?**

Proecss 1 will not run when process 0 is waiting for IO.

<br/>

5. **Now, run the same processes, but with the switching behavior set to switch to another process whenever one is WAITING for I/O (`-l 1:0,4:100 -c -S SWITCH_ON_IO`). What happens now? Use `-c` and `-p` to confirm that you are right.**

The same as problem 3
<br/>

6. **One other important behavior is what to do when an I/O completes. With `-I IO_RUN_LATER`, when an I/O completes, the process that issued it is not necessarily run right away; rather, whatever was running at the time keeps running. What happens when you run this combination of processes? (Run `./process-run.py -l 3:0,5:100,5:100,5:100 -S SWITCH_ON_IO -I IO_RUN_LATER -c -p`) Are system resources being effectively utilized?**

Process 0 runs the first IO then waits other process done to runs the remain IOs. No.
<br/>

7. **Now run the same processes, but with `-I IO_RUN_IMMEDIATE` set, which immediately runs the process that issued the I/O. How does this behavior differ? Why might running a process that just completed an I/O again be a good idea?**

Now other proecss can run when process 0 is waiting IO. More fair and reduce response time.
<br/>

8. **Now run with some randomly generated processes: `-s 1 -l 3:50,3:50` or `-s 2 -l 3:50,3:50` or `-s 3 -l 3:50,3:50`. See if you can predict how the trace will turn out. What happens when you use the flag `-I IO_RUN_IMMEDIATE` vs. `-I IO_RUN_LATER`? What happens when you use `-S SWITCH_ON_IO` vs. `-S SWITCH_ON_END`?**
2 changes: 1 addition & 1 deletion README.md
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Expand Up @@ -11,7 +11,7 @@ If you want to contribute or found some mistake just send me email at [ahmedbila
if the above link does not work [Slides by Prof. Kai Dong](https://mega.nz/#F!5EJWQLTb!Yh-BmhHr31xi406K0UQIrQ)

## Index

* [Chapter 4](https://github.com/KimbingNg/OSTEP-Solution/tree/master/Chapter%204)
* [Chapter 5](https://github.com/ahmedbilal/OSTEP-Solution/tree/master/Chapter%205)
* [Chapter 6](https://github.com/ahmedbilal/OSTEP-Solution/tree/master/Chapter%206)
* [Chapter 7](https://github.com/ahmedbilal/OSTEP-Solution/tree/master/Chapter%207)
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