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操作系统为了实现支持多任务处理的需要，一般都会支持多进程的机制，所以进程的的切换是内核当中一个非常重要的功能模块，其它几个功能模块主要有
处理器管理
内存管理
磁盘管理
输入输出管理
进程管理
本次实验主要是模拟了内核中的进程切换机制，以便加深对内核进程切换的理解。其中本次实验主要涉及以下三个代码文件。
mypcb.h
1 /* 2 * linux/mykernel/mypcb.h 3 * 4 * Kernel internal PCB types 5 * 6 * Copyright (C) 2013 Mengning 7 * 8 */ 9 10 #define MAX_TASK_NUM 4 11 #define KERNEL_STACK_SIZE 1024*8 12 13 /* CPU-specific state of this task */ 14 struct Thread { 15 unsigned long ip; 16 unsigned long sp; 17 }; 18 19 typedef struct PCB{ 20 int pid; 21 volatile long state; /* -1 unrunnable, 0 runnable, >0 stopped */ 22 char stack[KERNEL_STACK_SIZE]; 23 /* CPU-specific state of this task */ 24 struct Thread thread; 25 unsigned long task_entry; 26 struct PCB *next; 27 }tPCB; 28 29 void my_schedule(void);
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 }
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 }
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原文地址：http://www.cnblogs.com/qtalker/p/4340088.html
