OSTEP：抽象：进程
此系列主要完成操作系统导论（Operating Systems: Three Easy Pieces）的课后作业，还会涉及一些每章总结和感悟，大部分的题目都没有一个标准的答案，有争议和错误的地方欢迎同学们一起讨论。
相关资源
Website：http://www.ostep.org/
Homework：https://github.com/remzi-arpacidusseau/ostep-homework/
习题答案
注：本章习题需要安装Python才能继续完成。
首先使用-H命令查看process-run.py中的一些选项：
yzy@yzy-virtual-machine:~/ostep-homework/cpu-intro$ python3 process-run.py -h
Usage: process-run.py [options]
Options:
-h, --help show this help message and exit
-s SEED, --seed=SEED the random seed
-P PROGRAM, --program=PROGRAM
more specific controls over programs
-l PROCESS_LIST, --processlist=PROCESS_LIST
a comma-separated list of processes to run, in the
form X1:Y1,X2:Y2,... where X is the number of
instructions that process should run, and Y the
chances (from 0 to 100) that an instruction will use
the CPU or issue an IO
-L IO_LENGTH, --iolength=IO_LENGTH
how long an IO takes
-S PROCESS_SWITCH_BEHAVIOR, --switch=PROCESS_SWITCH_BEHAVIOR
when to switch between processes: SWITCH_ON_IO,
SWITCH_ON_END
-I IO_DONE_BEHAVIOR, --iodone=IO_DONE_BEHAVIOR
type of behavior when IO ends: IO_RUN_LATER,
IO_RUN_IMMEDIATE
-c compute answers for me
-p, --printstats print statistics at end; only useful with -c flag
(otherwise stats are not printed)
1.应该是100%,因为其中没有IO操作，全部都是CPU占用。
yzy@yzy-virtual-machine:~/ostep-homework/cpu-intro$ python3 process-run.py -l 5:100,5:100 -c -p
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 RUN:cpu READY 1
6 DONE RUN:cpu 1
7 DONE RUN:cpu 1
8 DONE RUN:cpu 1
9 DONE RUN:cpu 1
10 DONE RUN:cpu 1
Stats: Total Time 10
Stats: CPU Busy 10 (100.00%)
Stats: IO Busy 0 (0.00%)
2.4(进程 0) + 6(进程 1 IO) + 1 = 11
yzy@yzy-virtual-machine:~/ostep-homework/cpu-intro$ python3 process-run.py -l 4:100,1:0 -c -p
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 WAITING 1
11* DONE RUN:io_done 1
Stats: Total Time 11
Stats: CPU Busy 6 (54.55%)
Stats: IO Busy 5 (45.45%)
3.只花了7S，因为在进程1与IO交互时，放开了CPU的控制，使得进程0可以直接运行了。
yzy@yzy-virtual-machine:~/ostep-homework/cpu-intro$ python3 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 WAITING DONE 1
7* RUN:io_done DONE 1
Stats: Total Time 7
Stats: CPU Busy 6 (85.71%)
Stats: IO Busy 5 (71.43%)
4.再次回到11S，因为CPU和IO不能同时工作了。
yzy@yzy-virtual-machine:~/ostep-homework/cpu-intro$ python3 process-run.py -l 1:0,4:100 -c -p -S SWITCH_ON_END
Time PID: 0 PID: 1 CPU IOs
1 RUN:io READY 1
2 WAITING READY 1
3 WAITING READY 1
4 WAITING READY 1
5 WAITING READY 1
6 WAITING READY 1
7* RUN:io_done READY 1
8 DONE RUN:cpu 1
9 DONE RUN:cpu 1
10 DONE RUN:cpu 1
11 DONE RUN:cpu 1
Stats: Total Time 11
Stats: CPU Busy 6 (54.55%)
Stats: IO Busy 5 (45.45%)
5.回到7S，与第3题相同。
yzy@yzy-virtual-machine:~/ostep-homework/cpu-intro$ python3 process-run.py -l 1:0,4:100 -c -p -S SWITCH_ON_IO
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 WAITING DONE 1
7* RUN:io_done DONE 1
Stats: Total Time 7
Stats: CPU Busy 6 (85.71%)
Stats: IO Busy 5 (71.43%)
6.并不能有效利用，因为进程0运行完第一个IO后，不会立刻运行，而是等待其他进程运行完毕后才会继续运行IO，导致一部分时间内，IO和CPU没有同时被使用，浪费了时间。
yzy@yzy-virtual-machine:~/ostep-homework/cpu-intro$ python3 process-run.py -l 3:0,5:100,5:100,5:100 -c -p -S SWITCH_ON_IO -I IO_RUN_LATER
Time PID: 0 PID: 1 PID: 2 PID: 3 CPU IOs
1 RUN:io READY READY READY 1
2 WAITING RUN:cpu READY READY 1 1
3 WAITING RUN:cpu READY READY 1 1
4 WAITING RUN:cpu READY READY 1 1
5 WAITING RUN:cpu READY READY 1 1
6 WAITING RUN:cpu READY READY 1 1
7* READY DONE RUN:cpu READY 1
8 READY DONE RUN:cpu READY 1
9 READY DONE RUN:cpu READY 1
10 READY DONE RUN:cpu READY 1
11 READY DONE RUN:cpu READY 1
12 READY DONE DONE RUN:cpu 1
13 READY DONE DONE RUN:cpu 1
14 READY DONE DONE RUN:cpu 1
15 READY DONE DONE RUN:cpu 1
16 READY DONE DONE RUN:cpu 1
17 RUN:io_done DONE DONE DONE 1
18 RUN:io DONE DONE DONE 1
19 WAITING DONE DONE DONE 1
20 WAITING DONE DONE DONE 1
21 WAITING DONE DONE DONE 1
22 WAITING DONE DONE DONE 1
23 WAITING DONE DONE DONE 1
24* RUN:io_done DONE DONE DONE 1
25 RUN:io DONE DONE DONE 1
26 WAITING DONE DONE DONE 1
27 WAITING DONE DONE DONE 1
28 WAITING DONE DONE DONE 1
29 WAITING DONE DONE DONE 1
30 WAITING DONE DONE DONE 1
31* RUN:io_done DONE DONE DONE 1
Stats: Total Time 31
Stats: CPU Busy 21 (67.74%)
Stats: IO Busy 15 (48.39%)
7.进程0在IO结束直接运行，然后继续运行下一轮IO，此时其他进程可以去使用CPU，会尽量保证IO和CPU都能够同时利用。
yzy@yzy-virtual-machine:~/ostep-homework/cpu-intro$ python3 process-run.py -l 3:0,5:100,5:100,5:100 -c -p -S SWITCH_ON_IO -I IO_RUN_IMMEDIATE
Time PID: 0 PID: 1 PID: 2 PID: 3 CPU IOs
1 RUN:io READY READY READY 1
2 WAITING RUN:cpu READY READY 1 1
3 WAITING RUN:cpu READY READY 1 1
4 WAITING RUN:cpu READY READY 1 1
5 WAITING RUN:cpu READY READY 1 1
6 WAITING RUN:cpu READY READY 1 1
7* RUN:io_done DONE READY READY 1
8 RUN:io DONE READY READY 1
9 WAITING DONE RUN:cpu READY 1 1
10 WAITING DONE RUN:cpu READY 1 1
11 WAITING DONE RUN:cpu READY 1 1
12 WAITING DONE RUN:cpu READY 1 1
13 WAITING DONE RUN:cpu READY 1 1
14* RUN:io_done DONE DONE READY 1
15 RUN:io DONE DONE READY 1
16 WAITING DONE DONE RUN:cpu 1 1
17 WAITING DONE DONE RUN:cpu 1 1
18 WAITING DONE DONE RUN:cpu 1 1
19 WAITING DONE DONE RUN:cpu 1 1
20 WAITING DONE DONE RUN:cpu 1 1
21* RUN:io_done DONE DONE DONE 1
Stats: Total Time 21
Stats: CPU Busy 21 (100.00%)
Stats: IO Busy 15 (71.43%)
8.随机测试
总结与感悟
- 进程就是一段运行中的程序。其有一些机器状态，其中核心的就是内存、寄存器（程序计数器、栈指针等等）。
- 当运行程序时，操作系统首先将代码和静态数据加载到进程的内存中。然后分配一些内存给进程的运行时栈（用于保存一些局部变量、函数参数、返回地址等）。分配一些内存给进程的堆（显示请求的动态分配数据、全局变量等）。进行一些其他的初始化任务，比如初始化IO等。
- 进程状态分为运行、就绪、阻塞。