学号023作品
本实验资源来源： https://github.com/mengning/linuxkernel/
一、观察简易操作系统
此处使用实验楼的虚拟机打开终端
cd LinuxKernel/linux-3.9.4
rm -rf mykernel
patch -p1 < ../mykernel_for_linux3.9.4sc.patch
make allnoconfig
make ＃编译内核请耐心等待
qemu -kernel arch/x86/boot/bzImage
在QEMU窗口中我们可以看到一个运行中的简易操作系统，并输出字符串：
>>>>>my_timer_handler here<<<<<
和my_start_kernel here
运行截图如下：
在此处分析一下mymain.c和myinterrupt.c
mymain.c
在my_start_kernel函数中有一个循环，不停地输出my_start_kernel here
通过时钟中断周期函数调用my_timer_handler函数，可输出>>>>>my_timer_handler here<<<<<的字符串
总而言之，在mykernel启动之后，系统调用my_start_kernel函数，并利用时钟中断周期函数周期性调用my_timer_handler函数。
二、一个简单的时间片轮转多道程序分析
1、从https://github.com/mengning/mykernel/tree/master/mykernel-1.1上获取mymain.c、myinterrupt.c、pcb.c三个文件
2、在mykernel文件下覆盖mymain.c、myinterrupt.c，并新建pcb.c文件
3、cd linux-3.9.4 执行下列命令，重新编译内核
make allnoconfig
make
qemu -kernel arch/x86/boot/bzImage
运行截图如下：
可见系统进程在切换
以下进行代码分析
mypcb.h ： 进程控制块PCB结构体定义。
mymain.c： 初始化各个进程并启动0号进程。
myinterrupt.c：时钟中断处理和进程调度算法。
mypcb.h：
1 /* mykernel--Simple simulation of the linux OS process schedule
2 *
3 * linux/mykernel/mypcb.h
4 *
5 * Kernel internal my_timer_handler
6 *
7 * Copyright (C) 2013 Mengning
8 *
9 * Modified 2014 Yunquan Zhang <zhangyunquan@hotmail.com>
10 *
11 *
12 * You can redistribute or modify this program under the terms
13 * of the GNU General Public License as published by
14 * the Free Software Foundation.
15 *
16 * You should have received a copy of the GNU General Public License
17 * along with this program. If not, see <http://www.gnu.org/licenses/>.
18 */
19
20 #define MAX_TASK_NUM 10 // max num of task in system
21 #define KERNEL_STACK_SIZE 1024*8
22 #define PRIORITY_MAX 30 //priority range from 0 to 30
23
24 /* CPU-specific state of this task */
25 struct Thread {
26 unsigned long ip;//point to cpu run address
27 unsigned long sp;//point to the thread stack‘s top address
28 //todo add other attrubte of system thread
29 };
30 //PCB Struct
31 typedef struct PCB{
32 int pid; // pcb id
33 volatile long state; /* -1 unrunnable, 0 runnable, >0 stopped */
34 char stack[KERNEL_STACK_SIZE];// each pcb stack size is 1024*8
35 /* CPU-specific state of this task */
36 struct Thread thread;
37 unsigned long task_entry;//the task execute entry memory address
38 struct PCB *next;//pcb is a circular linked list
39 unsigned long priority;// task priority ////////
40 //todo add other attrubte of process control block
41 }tPCB;
42
43 //void my_schedule(int pid);
44 void my_schedule(void);
在这个文件里，定义了 Thread 结构体，用于存储当前进程中正在执行的线程的ip和sp，PCB结构体中的各个字段含义如下
pid：进程号
state：进程状态，在模拟系统中，所有进程控制块信息都会被创建出来，其初始化值就是-1，如果被调度运行起来，其值就会变成0
stack：进程使用的堆栈
thread：当前正在执行的线程信息
task_entry：进程入口函数
next：指向下一个PCB，模拟系统中所有的PCB是以链表的形式组织起来的。
my_schedule声明，在myinterrupt.c中实现，在mymain.c中的各个进程函数会根据一个全局变量的状态来决定是否调用它，从而实现主动调度。
mymain.c
1 /*
2 * linux/mykernel/mymain.c
3 *
4 * Kernel internal my_start_kernel
5 *
6 * Copyright (C) 2013 Mengning
7 *
8 */
9 #include <linux/types.h>
10 #include <linux/string.h>
11 #include <linux/ctype.h>
12 #include <linux/tty.h>
13 #include <linux/vmalloc.h>
14
15
16 #include "mypcb.h"
17
18 tPCB task[MAX_TASK_NUM];
19 tPCB * my_current_task = NULL;
20 volatile int my_need_sched = 0;
21
22 void my_process(void);
23
24
25 void __init my_start_kernel(void)
26 {
27 int pid = 0;
28 int i;
29 /* Initialize process 0*/
30 task[pid].pid = pid;
31 task[pid].state = 0;/* -1 unrunnable, 0 runnable, >0 stopped */
32 task[pid].task_entry = task[pid].thread.ip = (unsigned long)my_process;
33 task[pid].thread.sp = (unsigned long)&task[pid].stack[KERNEL_STACK_SIZE-1];
34 task[pid].next = &task[pid];
35 /*fork more process */
36 for(i=1;i<MAX_TASK_NUM;i++)
37 {
38 memcpy(&task[i],&task[0],sizeof(tPCB));
39 task[i].pid = i;
40 task[i].state = -1;
41 task[i].thread.sp = (unsigned long)&task[i].stack[KERNEL_STACK_SIZE-1];
42 task[i].next = task[i-1].next;
43 task[i-1].next = &task[i];
44 }
45 /* start process 0 by task[0] */
46 pid = 0;
47 my_current_task = &task[pid];
48 asm volatile(
49 "movl %1,%%esp\n\t" /* set task[pid].thread.sp to esp */
50 "pushl %1\n\t" /* push ebp */
51 "pushl %0\n\t" /* push task[pid].thread.ip */
52 "ret\n\t" /* pop task[pid].thread.ip to eip */
53 "popl %%ebp\n\t"
54 :
55 : "c" (task[pid].thread.ip),"d" (task[pid].thread.sp) /* input c or d mean %ecx/%edx*/
56 );
57 }
58 void my_process(void)
59 {
60 int i = 0;
61 while(1)
62 {
63 i++;
64 if(i%10000000 == 0)
65 {
66 printk(KERN_NOTICE "this is process %d -\n",my_current_task->pid);
67 if(my_need_sched == 1)
68 {
69 my_need_sched = 0;
70 my_schedule();
71 }
72 printk(KERN_NOTICE "this is process %d +\n",my_current_task->pid);
73 }
74 }
75 }
my_start_kernel 是系统启动后最先调用的函数，在这个函数里完成了0号进程的初始化和启动，并创建了其它的进程PCB，以方便后面的调度。在模拟系统里，每个进程的函数代码都是一样的，即 my_process 函数，my_process 在执行的时候，会打印出当前进程的 id，从而使得我们能够看到当前哪个进程正在执行。
myinterrupt.c
1 /*
2 * linux/mykernel/myinterrupt.c
3 *
4 * Kernel internal my_timer_handler
5 *
6 * Copyright (C) 2013 Mengning
7 *
8 */
9 #include <linux/types.h>
10 #include <linux/string.h>
11 #include <linux/ctype.h>
12 #include <linux/tty.h>
13 #include <linux/vmalloc.h>
14
15 #include "mypcb.h"
16
17 extern tPCB task[MAX_TASK_NUM];
18 extern tPCB * my_current_task;
19 extern volatile int my_need_sched;
20 volatile int time_count = 0;
21
22 /*
23 * Called by timer interrupt.
24 * it runs in the name of current running process,
25 * so it use kernel stack of current running process
26 */
27 void my_timer_handler(void)
28 {
29 #if 1
30 if(time_count%1000 == 0 && my_need_sched != 1)
31 {
32 printk(KERN_NOTICE ">>>my_timer_handler here<<<\n");
33 my_need_sched = 1;
34 }
35 time_count ++ ;
36 #endif
37 return;
38 }
39
40 void my_schedule(void)
41 {
42 tPCB * next;
43 tPCB * prev;
44
45 if(my_current_task == NULL
46 || my_current_task->next == NULL)
47 {
48 return;
49 }
50 printk(KERN_NOTICE ">>>my_schedule<<<\n");
51 /* schedule */
52 next = my_current_task->next;
53 prev = my_current_task;
54 if(next->state == 0)/* -1 unrunnable, 0 runnable, >0 stopped */
55 {
56 /* switch to next process */
57 asm volatile(
58 "pushl %%ebp\n\t" /* save ebp */
59 "movl %%esp,%0\n\t" /* save esp */
60 "movl %2,%%esp\n\t" /* restore esp */
61 "movl $1f,%1\n\t" /* save eip */
62 "pushl %3\n\t"
63 "ret\n\t" /* restore eip */
64 "1:\t" /* next process start here */
65 "popl %%ebp\n\t"
66 : "=m" (prev->thread.sp),"=m" (prev->thread.ip)
67 : "m" (next->thread.sp),"m" (next->thread.ip)
68 );
69 my_current_task = next;
70 printk(KERN_NOTICE ">>>switch %d to %d<<<\n",prev->pid,next->pid);
71 }
72 else
73 {
74 next->state = 0;
75 my_current_task = next;
76 printk(KERN_NOTICE ">>>switch %d to %d<<<\n",prev->pid,next->pid);
77 /* switch to new process */
78 asm volatile(
79 "pushl %%ebp\n\t" /* save ebp */
80 "movl %%esp,%0\n\t" /* save esp */
81 "movl %2,%%esp\n\t" /* restore esp */
82 "movl %2,%%ebp\n\t" /* restore ebp */
83 "movl $1f,%1\n\t" /* save eip */
84 "pushl %3\n\t"
85 "ret\n\t" /* restore eip */
86 : "=m" (prev->thread.sp),"=m" (prev->thread.ip)
87 : "m" (next->thread.sp),"m" (next->thread.ip)
88 );
89 }
90 return;
91 }
my_time_handler()函数，是个时间片轮转，周期性地发出中断信号，也就是my_need_sched。my_start_kernel()完成每个进程初始化，每个进程的任务都是my_process(),由于这个函数中有个无限循环，任务永远不会结束；并且启动了0号进程。任务需要调度时根据任务链表顺序进行调度。
实验总结
通过本次实验，对于进程调度和中断有了更加深刻的了解。总的来说，操作系统的工作需要进行进程的启动与切换，切换时需要保存上下文，切换的程序完成后需要恢复上下文，进程切换通过时钟中断进行控制。
原文地址：https://www.cnblogs.com/LucasChang/p/10518364.html