OSTEP Chapter 4 回顾
OSTEP的全称是Operating Systems: Three Easy Pieces，是一本很好的操作系统入门书，之所以再看这本书，是因为学习xv6碰到了不少困难，希望结合多个教材一起学习，后续会给出大部分章节的回顾，这里从第4章开始，本章介绍了抽象：进程。
书籍介绍：
学习资料：
- https://pages.cs.wisc.edu/~remzi/OSTEP/
- https://github.com/remzi-arpacidusseau/ostep-translations/tree/master/chinese
- https://github.com/joshuap233/Operating-Systems-Three-Easy-Pieces-NOTES
第4 章 抽象：进程
内容回顾
关键概念
- 进程：运行中的程序。
- 虚拟化：
- 需要低级机制和高级智能来支持；
- 低级机制：称为机制，为系统的“如何（how）”问题提供答案；
- 高级智能：称为策略，为系统的“哪个（which）”问题提供答案；
- 时分共享（time sharing）：允许资源由一个实体使用一小段时间，然后由另一个实体使用一小段时间。
- 进程API：
- 创建（create）；
- 销毁（destroy）；
- 等待（wait）；
- 其他控制（miscellaneous control）；
- 状态（statu）；
- 进程状态：
- 运行（running）；
- 就绪（ready）；
- 阻塞（blocked）；
作业
1
(base) λ python ./process-run.py -l 5:100,5:100
Produce a trace of what would happen when you run these processes:
Process 0
cpu
cpu
cpu
cpu
cpu
Process 1
cpu
cpu
cpu
cpu
cpu
Important behaviors:
System will switch when the current process is FINISHED or ISSUES AN IO
After IOs, the process issuing the IO will run LATER (when it is its turn)CPU利用率是100%，因为5:100表示执行5个指令，CPU执行的机会为100%，验证这点：
(base) λ python ./process-run.py -l 5:100,5:100 -c
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 12
需要11个clock ticks，因为4:100需要4个clock ticks，此时使用CPU，无法进行IO；1:0需要进行IO，分别经历RUN:io，RUN:io_done以及WAITING状态，其中WAITING需要iolength个clock ticks，默认值为5，因此总共需要4 + 2 + 5 = 11个clock ticks。
验证：
λ python ./process-run.py -l 4:100,1:0 -c
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 3
需要7个clock ticks，因为进程0先进入RUN:io状态，然后进入WAITING状态，需要5个clock ticks；此时系统切换到进程1，进程1进入RUN:cpu状态，需要4个clock ticks；最后进程0进入RUN:io_done状态，注意此时进程1进入DONE状态。
验证：
(base) λ python ./process-run.py -l 1:0,4:100 -c
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 14
因为进程在进行I/O时不会进行切换，所以此时和第2题的结果相同。
验证：
(base) λ python ./process-run.py -l 1:0,4:100 -c -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 15
因为进程在进行I/O时会进行切换，所以此时和第3题的结果相同。
验证：
(base) λ python ./process-run.py -l 1:0,4:100 -c -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 16
当第一次I/O完成时，发出的进程没有马上进入RUN:io_done状态，只有等到其他CPU任务完成时，才会进入RUN:io_done状态，然后才能执行后续I/O。这样效率较低，因为可以在I/O的同时执行CPU任务：
(base) λ python ./process-run.py -l 3:0,5:100,5:100,5:100 -S SWITCH_ON_IO -I IO_RUN_LATER -c -p
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
当第一次I/O完成时，发出的进程马上进入RUN:io_done，然后可以立即进入RUN:io状态，随后进入WAITING状态，与此同时其他CPU任务可以运行，从而提高CPU利用率：
(base) λ python ./process-run.py -l 3:0,5:100,5:100,5:100 -S SWITCH_ON_IO -I IO_RUN_IMMEDIATE -c -p
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
seed=1
(base) λ python ./process-run.py -s 1 -l 3:50,3:50
Produce a trace of what would happen when you run these processes:
Process 0
cpu
io
io_done
io
io_done
Process 1
cpu
cpu
cpu-I IO_RUN_IMMEDIATE参数：
(base) λ python ./process-run.py -s 1 -l 3:50,3:50 -I IO_RUN_IMMEDIATE -c -p
Time PID: 0 PID: 1 CPU IOs
1 RUN:cpu READY 1
2 RUN:io READY 1
3 WAITING RUN:cpu 1 1
4 WAITING RUN:cpu 1 1
5 WAITING RUN:cpu 1 1
6 WAITING DONE 1
7 WAITING DONE 1
8* RUN:io_done DONE 1
9 RUN:io DONE 1
10 WAITING DONE 1
11 WAITING DONE 1
12 WAITING DONE 1
13 WAITING DONE 1
14 WAITING DONE 1
15* RUN:io_done DONE 1
Stats: Total Time 15
Stats: CPU Busy 8 (53.33%)
Stats: IO Busy 10 (66.67%)-I IO_RUN_LATER参数，注意CPU任务只需要3个clock ticks（< IO时间），所以和之前情形相同：
(base) λ python ./process-run.py -s 1 -l 3:50,3:50 -I IO_RUN_LATER -c -p
Time PID: 0 PID: 1 CPU IOs
1 RUN:cpu READY 1
2 RUN:io READY 1
3 WAITING RUN:cpu 1 1
4 WAITING RUN:cpu 1 1
5 WAITING RUN:cpu 1 1
6 WAITING DONE 1
7 WAITING DONE 1
8* RUN:io_done DONE 1
9 RUN:io DONE 1
10 WAITING DONE 1
11 WAITING DONE 1
12 WAITING DONE 1
13 WAITING DONE 1
14 WAITING DONE 1
15* RUN:io_done DONE 1
Stats: Total Time 15
Stats: CPU Busy 8 (53.33%)
Stats: IO Busy 10 (66.67%)-S SWITCH_ON_IO参数：
(base) λ python ./process-run.py -s 1 -l 3:50,3:50 -S SWITCH_ON_IO -c -p
Time PID: 0 PID: 1 CPU IOs
1 RUN:cpu READY 1
2 RUN:io READY 1
3 WAITING RUN:cpu 1 1
4 WAITING RUN:cpu 1 1
5 WAITING RUN:cpu 1 1
6 WAITING DONE 1
7 WAITING DONE 1
8* RUN:io_done DONE 1
9 RUN:io DONE 1
10 WAITING DONE 1
11 WAITING DONE 1
12 WAITING DONE 1
13 WAITING DONE 1
14 WAITING DONE 1
15* RUN:io_done DONE 1
Stats: Total Time 15
Stats: CPU Busy 8 (53.33%)
Stats: IO Busy 10 (66.67%)-S SWITCH_ON_END参数，在I/O完成时才会切换进程：
(base) λ python ./process-run.py -s 1 -l 3:50,3:50 -S SWITCH_ON_END -c -p
Time PID: 0 PID: 1 CPU IOs
1 RUN:cpu READY 1
2 RUN:io READY 1
3 WAITING READY 1
4 WAITING READY 1
5 WAITING READY 1
6 WAITING READY 1
7 WAITING READY 1
8* RUN:io_done READY 1
9 RUN:io READY 1
10 WAITING READY 1
11 WAITING READY 1
12 WAITING READY 1
13 WAITING READY 1
14 WAITING READY 1
15* RUN:io_done READY 1
16 DONE RUN:cpu 1
17 DONE RUN:cpu 1
18 DONE RUN:cpu 1
Stats: Total Time 18
Stats: CPU Busy 8 (44.44%)
Stats: IO Busy 10 (55.56%)seed=2
(base) λ python ./process-run.py -s 2 -l 3:50,3:50
Produce a trace of what would happen when you run these processes:
Process 0
io
io_done
io
io_done
cpu
Process 1
cpu
io
io_done
io
io_done
Important behaviors:
System will switch when the current process is FINISHED or ISSUES AN IO
After IOs, the process issuing the IO will run LATER (when it is its turn)-I IO_RUN_IMMEDIATE参数：
(base) λ python ./process-run.py -s 2 -l 3:50,3:50 -I IO_RUN_IMMEDIATE -c -p
Time PID: 0 PID: 1 CPU IOs
1 RUN:io READY 1
2 WAITING RUN:cpu 1 1
3 WAITING RUN:io 1 1
4 WAITING WAITING 2
5 WAITING WAITING 2
6 WAITING WAITING 2
7* RUN:io_done WAITING 1 1
8 RUN:io WAITING 1 1
9* WAITING RUN:io_done 1 1
10 WAITING RUN:io 1 1
11 WAITING WAITING 2
12 WAITING WAITING 2
13 WAITING WAITING 2
14* RUN:io_done WAITING 1 1
15 RUN:cpu WAITING 1 1
16* DONE RUN:io_done 1
Stats: Total Time 16
Stats: CPU Busy 10 (62.50%)
Stats: IO Busy 14 (87.50%)-I IO_RUN_LATER参数：
(base) λ python ./process-run.py -s 2 -l 3:50,3:50 -I IO_RUN_LATER -c -p
Time PID: 0 PID: 1 CPU IOs
1 RUN:io READY 1
2 WAITING RUN:cpu 1 1
3 WAITING RUN:io 1 1
4 WAITING WAITING 2
5 WAITING WAITING 2
6 WAITING WAITING 2
7* RUN:io_done WAITING 1 1
8 RUN:io WAITING 1 1
9* WAITING RUN:io_done 1 1
10 WAITING RUN:io 1 1
11 WAITING WAITING 2
12 WAITING WAITING 2
13 WAITING WAITING 2
14* RUN:io_done WAITING 1 1
15 RUN:cpu WAITING 1 1
16* DONE RUN:io_done 1
Stats: Total Time 16
Stats: CPU Busy 10 (62.50%)
Stats: IO Busy 14 (87.50%)-S SWITCH_ON_IO参数：
(base) λ python ./process-run.py -s 2 -l 3:50,3:50 -S SWITCH_ON_IO -c -p
Time PID: 0 PID: 1 CPU IOs
1 RUN:io READY 1
2 WAITING RUN:cpu 1 1
3 WAITING RUN:io 1 1
4 WAITING WAITING 2
5 WAITING WAITING 2
6 WAITING WAITING 2
7* RUN:io_done WAITING 1 1
8 RUN:io WAITING 1 1
9* WAITING RUN:io_done 1 1
10 WAITING RUN:io 1 1
11 WAITING WAITING 2
12 WAITING WAITING 2
13 WAITING WAITING 2
14* RUN:io_done WAITING 1 1
15 RUN:cpu WAITING 1 1
16* DONE RUN:io_done 1
Stats: Total Time 16
Stats: CPU Busy 10 (62.50%)
Stats: IO Busy 14 (87.50%)-S SWITCH_ON_END参数，在I/O完成时才会切换进程：
(base) λ python ./process-run.py -s 2 -l 3:50,3:50 -S SWITCH_ON_END -c -p
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 RUN:io READY 1
9 WAITING READY 1
10 WAITING READY 1
11 WAITING READY 1
12 WAITING READY 1
13 WAITING READY 1
14* RUN:io_done READY 1
15 RUN:cpu READY 1
16 DONE RUN:cpu 1
17 DONE RUN:io 1
18 DONE WAITING 1
19 DONE WAITING 1
20 DONE WAITING 1
21 DONE WAITING 1
22 DONE WAITING 1
23* DONE RUN:io_done 1
24 DONE RUN:io 1
25 DONE WAITING 1
26 DONE WAITING 1
27 DONE WAITING 1
28 DONE WAITING 1
29 DONE WAITING 1
30* DONE RUN:io_done 1
Stats: Total Time 30
Stats: CPU Busy 10 (33.33%)
Stats: IO Busy 20 (66.67%)seed=3
(base) λ python ./process-run.py -s 3 -l 3:50,3:50
Produce a trace of what would happen when you run these processes:
Process 0
cpu
io
io_done
cpu
Process 1
io
io_done
io
io_done
cpu
Important behaviors:
System will switch when the current process is FINISHED or ISSUES AN IO
After IOs, the process issuing the IO will run LATER (when it is its turn)-I IO_RUN_IMMEDIATE参数：
(base) λ python ./process-run.py -s 3 -l 3:50,3:50 -I IO_RUN_IMMEDIATE -c -p
Time PID: 0 PID: 1 CPU IOs
1 RUN:cpu READY 1
2 RUN:io READY 1
3 WAITING RUN:io 1 1
4 WAITING WAITING 2
5 WAITING WAITING 2
6 WAITING WAITING 2
7 WAITING WAITING 2
8* RUN:io_done WAITING 1 1
9* READY RUN:io_done 1
10 READY RUN:io 1
11 RUN:cpu WAITING 1 1
12 DONE WAITING 1
13 DONE WAITING 1
14 DONE WAITING 1
15 DONE WAITING 1
16* DONE RUN:io_done 1
17 DONE RUN:cpu 1
Stats: Total Time 17
Stats: CPU Busy 9 (52.94%)
Stats: IO Busy 11 (64.71%)-I IO_RUN_LATER参数：
(base) λ python ./process-run.py -s 3 -l 3:50,3:50 -I IO_RUN_LATER -c -p
Time PID: 0 PID: 1 CPU IOs
1 RUN:cpu READY 1
2 RUN:io READY 1
3 WAITING RUN:io 1 1
4 WAITING WAITING 2
5 WAITING WAITING 2
6 WAITING WAITING 2
7 WAITING WAITING 2
8* RUN:io_done WAITING 1 1
9* RUN:cpu READY 1
10 DONE RUN:io_done 1
11 DONE RUN:io 1
12 DONE WAITING 1
13 DONE WAITING 1
14 DONE WAITING 1
15 DONE WAITING 1
16 DONE WAITING 1
17* DONE RUN:io_done 1
18 DONE RUN:cpu 1
Stats: Total Time 18
Stats: CPU Busy 9 (50.00%)
Stats: IO Busy 11 (61.11%)-S SWITCH_ON_IO参数：
(base) λ python ./process-run.py -s 3 -l 3:50,3:50 -S SWITCH_ON_IO -c -p
Time PID: 0 PID: 1 CPU IOs
1 RUN:cpu READY 1
2 RUN:io READY 1
3 WAITING RUN:io 1 1
4 WAITING WAITING 2
5 WAITING WAITING 2
6 WAITING WAITING 2
7 WAITING WAITING 2
8* RUN:io_done WAITING 1 1
9* RUN:cpu READY 1
10 DONE RUN:io_done 1
11 DONE RUN:io 1
12 DONE WAITING 1
13 DONE WAITING 1
14 DONE WAITING 1
15 DONE WAITING 1
16 DONE WAITING 1
17* DONE RUN:io_done 1
18 DONE RUN:cpu 1
Stats: Total Time 18
Stats: CPU Busy 9 (50.00%)
Stats: IO Busy 11 (61.11%)-S SWITCH_ON_END参数，在I/O完成时才会切换进程：
(base) λ python ./process-run.py -s 3 -l 3:50,3:50 -S SWITCH_ON_END -c -p
Time PID: 0 PID: 1 CPU IOs
1 RUN:cpu READY 1
2 RUN:io READY 1
3 WAITING READY 1
4 WAITING READY 1
5 WAITING READY 1
6 WAITING READY 1
7 WAITING READY 1
8* RUN:io_done READY 1
9 RUN:cpu READY 1
10 DONE RUN:io 1
11 DONE WAITING 1
12 DONE WAITING 1
13 DONE WAITING 1
14 DONE WAITING 1
15 DONE WAITING 1
16* DONE RUN:io_done 1
17 DONE RUN:io 1
18 DONE WAITING 1
19 DONE WAITING 1
20 DONE WAITING 1
21 DONE WAITING 1
22 DONE WAITING 1
23* DONE RUN:io_done 1
24 DONE RUN:cpu 1
Stats: Total Time 24
Stats: CPU Busy 9 (37.50%)
Stats: IO Busy 15 (62.50%)本博客所有文章除特别声明外，均采用 CC BY-NC-SA 4.0 许可协议。转载请注明来自 Doraemonzzz！
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