对一个简单的时间片轮转多道程序内核代码的浅析

 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 }