首先上header file
#ifndef _SCHED_H
#define _SCHED_H
#define HZ 100
#define NR_TASKS 64
#define TASK_SIZE 0x04000000
#define LIBRARY_SIZE 0x00400000
#if (TASK_SIZE & 0x3fffff)
#error "TASK_SIZE must be multiple of 4M"
#endif
#if (LIBRARY_SIZE & 0x3fffff)
#error "LIBRARY_SIZE must be a multiple of 4M"
#endif
#if (LIBRARY_SIZE >= (TASK_SIZE/2))
#error "LIBRARY_SIZE too damn big!"
#endif
#if (((TASK_SIZE>>16)*NR_TASKS) != 0x10000)
#error "TASK_SIZE*NR_TASKS must be 4GB"
#endif
#define LIBRARY_OFFSET (TASK_SIZE - LIBRARY_SIZE)
#define CT_TO_SECS(x) ((x) / HZ)
#define CT_TO_USECS(x) (((x) % HZ) * 1000000/HZ)
#define FIRST_TASK task[0]
#define LAST_TASK task[NR_TASKS-1]
#include <linux/head.h>
#include <linux/fs.h>
#include <linux/mm.h>
#include <sys/param.h>
#include <sys/time.h>
#include <sys/resource.h>
#include <signal.h>
#if (NR_OPEN > 32)
#error "Currently the close-on-exec-flags and select masks are in one long, max 32 files/proc"
#endif
#define TASK_RUNNING 0
#define TASK_INTERRUPTIBLE 1
#define TASK_UNINTERRUPTIBLE 2
#define TASK_ZOMBIE 3
#define TASK_STOPPED 4
#ifndef NULL
#define NULL ((void *) 0)
#endif
extern int copy_page_tables(unsigned long from, unsigned long to, long size);
extern int free_page_tables(unsigned long from, unsigned long size);
extern void sched_init(void);
extern void schedule(void);
extern void trap_init(void);
extern void panic(const char * str);
extern int tty_write(unsigned minor,char * buf,int count);
typedef int (*fn_ptr)();
struct i387_struct {
long cwd;
long swd;
long twd;
long fip;
long fcs;
long foo;
long fos;
long st_space[20]; /* 8*10 bytes for each FP-reg = 80 bytes */
};
struct tss_struct {
long back_link; /* 16 high bits zero */
long esp0;
long ss0; /* 16 high bits zero */
long esp1;
long ss1; /* 16 high bits zero */
long esp2;
long ss2; /* 16 high bits zero */
long cr3;
long eip;
long eflags;
long eax,ecx,edx,ebx;
long esp;
long ebp;
long esi;
long edi;
long es; /* 16 high bits zero */
long cs; /* 16 high bits zero */
long ss; /* 16 high bits zero */
long ds; /* 16 high bits zero */
long fs; /* 16 high bits zero */
long gs; /* 16 high bits zero */
long ldt; /* 16 high bits zero */
long trace_bitmap; /* bits: trace 0, bitmap 16-31 */
struct i387_struct i387;
};
struct task_struct {
/* these are hardcoded - don‘t touch */
long state; /* -1 unrunnable, 0 runnable, >0 stopped */
long counter;
long priority;
long signal;
struct sigaction sigaction[32];
long blocked; /* bitmap of masked signals */
/* various fields */
int exit_code;
unsigned long start_code,end_code,end_data,brk,start_stack;
long pid,pgrp,session,leader;
int groups[NGROUPS];
/*
* pointers to parent process, youngest child, younger sibling,
* older sibling, respectively. (p->father can be replaced with
* p->p_pptr->pid)
*/
struct task_struct *p_pptr, *p_cptr, *p_ysptr, *p_osptr;
unsigned short uid,euid,suid;
unsigned short gid,egid,sgid;
unsigned long timeout,alarm;
long utime,stime,cutime,cstime,start_time;
struct rlimit rlim[RLIM_NLIMITS];
unsigned int flags; /* per process flags, defined below */
unsigned short used_math;
/* file system info */
int tty; /* -1 if no tty, so it must be signed */
unsigned short umask;
struct m_inode * pwd;
struct m_inode * root;
struct m_inode * executable;
struct m_inode * library;
unsigned long close_on_exec;
struct file * filp[NR_OPEN];
/* ldt for this task 0 - zero 1 - cs 2 - ds&ss */
struct desc_struct ldt[3];
/* tss for this task */
struct tss_struct tss;
};
/*
* Per process flags
*/
#define PF_ALIGNWARN 0x00000001 /* Print alignment warning msgs */
/* Not implemented yet, only for 486*/
/*
* INIT_TASK is used to set up the first task table, touch at
* your own risk!. Base=0, limit=0x9ffff (=640kB)
*/
#define INIT_TASK /* state etc */ { 0,15,15, /* signals */ 0,{{},},0, /* ec,brk... */ 0,0,0,0,0,0, /* pid etc.. */ 0,0,0,0, /* suppl grps*/ {NOGROUP,}, /* proc links*/ &init_task.task,0,0,0, /* uid etc */ 0,0,0,0,0,0, /* timeout */ 0,0,0,0,0,0,0, /* rlimits */ { {0x7fffffff, 0x7fffffff}, {0x7fffffff, 0x7fffffff}, {0x7fffffff, 0x7fffffff}, {0x7fffffff, 0x7fffffff}, {0x7fffffff, 0x7fffffff}, {0x7fffffff, 0x7fffffff}}, /* flags */ 0, /* math */ 0, /* fs info */ -1,0022,NULL,NULL,NULL,NULL,0, /* filp */ {NULL,}, { {0,0}, /* ldt */ {0x9f,0xc0fa00}, {0x9f,0xc0f200}, }, /*tss*/ {0,PAGE_SIZE+(long)&init_task,0x10,0,0,0,0,(long)&pg_dir, 0,0,0,0,0,0,0,0, 0,0,0x17,0x17,0x17,0x17,0x17,0x17, _LDT(0),0x80000000, {} }, }
extern struct task_struct *task[NR_TASKS];
extern struct task_struct *last_task_used_math;
extern struct task_struct *current;
extern unsigned long volatile jiffies;
extern unsigned long startup_time;
extern int jiffies_offset;
#define CURRENT_TIME (startup_time+(jiffies+jiffies_offset)/HZ)
extern void add_timer(long jiffies, void (*fn)(void));
extern void sleep_on(struct task_struct ** p);
extern void interruptible_sleep_on(struct task_struct ** p);
extern void wake_up(struct task_struct ** p);
extern int in_group_p(gid_t grp);
/*
* Entry into gdt where to find first TSS. 0-nul, 1-cs, 2-ds, 3-syscall
* 4-TSS0, 5-LDT0, 6-TSS1 etc ...
*/
#define FIRST_TSS_ENTRY 4
#define FIRST_LDT_ENTRY (FIRST_TSS_ENTRY+1)
#define _TSS(n) ((((unsigned long) n)<<4)+(FIRST_TSS_ENTRY<<3))
#define _LDT(n) ((((unsigned long) n)<<4)+(FIRST_LDT_ENTRY<<3))
#define ltr(n) __asm__("ltr %%ax"::"a" (_TSS(n)))
#define lldt(n) __asm__("lldt %%ax"::"a" (_LDT(n)))
#define str(n) __asm__("str %%ax\n\t" "subl %2,%%eax\n\t" "shrl $4,%%eax" :"=a" (n) :"a" (0),"i" (FIRST_TSS_ENTRY<<3))
/*
* switch_to(n) should switch tasks to task nr n, first
* checking that n isn‘t the current task, in which case it does nothing.
* This also clears the TS-flag if the task we switched to has used
* tha math co-processor latest.
*/
#define switch_to(n) {struct {long a,b;} __tmp; __asm__("cmpl %%ecx,_current\n\t" "je 1f\n\t" "movw %%dx,%1\n\t" "xchgl %%ecx,_current\n\t" "ljmp %0\n\t" "cmpl %%ecx,_last_task_used_math\n\t" "jne 1f\n\t" "clts\n" "1:" ::"m" (*&__tmp.a),"m" (*&__tmp.b), "d" (_TSS(n)),"c" ((long) task[n])); }
#define PAGE_ALIGN(n) (((n)+0xfff)&0xfffff000)
#define _set_base(addr,base) __asm__("movw %%dx,%0\n\t" "rorl $16,%%edx\n\t" "movb %%dl,%1\n\t" "movb %%dh,%2" ::"m" (*((addr)+2)), "m" (*((addr)+4)), "m" (*((addr)+7)), "d" (base) :"dx")
#define _set_limit(addr,limit) __asm__("movw %%dx,%0\n\t" "rorl $16,%%edx\n\t" "movb %1,%%dh\n\t" "andb $0xf0,%%dh\n\t" "orb %%dh,%%dl\n\t" "movb %%dl,%1" ::"m" (*(addr)), "m" (*((addr)+6)), "d" (limit) :"dx")
#define set_base(ldt,base) _set_base( ((char *)&(ldt)) , base )
#define set_limit(ldt,limit) _set_limit( ((char *)&(ldt)) , (limit-1)>>12 )
#define _get_base(addr) ({unsigned long __base; __asm__("movb %3,%%dh\n\t" "movb %2,%%dl\n\t" "shll $16,%%edx\n\t" "movw %1,%%dx" :"=d" (__base) :"m" (*((addr)+2)), "m" (*((addr)+4)), "m" (*((addr)+7))); __base;})
#define get_base(ldt) _get_base( ((char *)&(ldt)) )
#define get_limit(segment) ({ unsigned long __limit; __asm__("lsll %1,%0\n\tincl %0":"=r" (__limit):"r" (segment)); __limit;})
#endif
每个任务都有两个堆栈，分别用于用户态和内核态程序的执行，并且分别称为用户态堆栈和内核态堆栈。处于不同的CPU特权级中，这两个堆栈之间的主要区别在于任务的内核态堆栈很小，所保存的数量最多不能超过4096-任务数据结构块个字节，大约为3K，而任务的用户态堆栈却可以在用户的64M空间内延伸。
void show_task(int nr,struct task_struct * p)//显示p指向的nr号进程的相关信息
{
int i,j = 4096-sizeof(struct task_struct);//j记录了任务数据结构之后的堆栈空间大小
printk("%d: pid=%d, state=%d, father=%d, child=%d, ",nr,p->pid,
p->state, p->p_pptr->pid, p->p_cptr ? p->p_cptr->pid : -1);//打印关于p指向进程的各种信息
i=0;
while (i<j && !((char *)(p+1))[i])//很巧妙的计算了任务数据结构之后的空字节(数据内容为0)的大小
i++;
printk("%d/%d chars free in kstack\n\r",i,j);//内核栈最大为j，空字节数是i，分数比率i/j
printk(" PC=%08X.", *(1019 + (unsigned long *) p));
//p指向结构体起始地址偏移1019,应该是指数据结构中的TSS结构内EIP处的值（所谓PC指针）,eip的值即当前任务用户态的代码指针。
if (p->p_ysptr || p->p_osptr) //如果p进程有同辈的进程，那么打印它们的进程号
printk(" Younger sib=%d, older sib=%d\n\r",
p->p_ysptr ? p->p_ysptr->pid : -1,
p->p_osptr ? p->p_osptr->pid : -1);
else
printk("\n\r");
}关于show_task讨论的一些帖子
http://www.oldlinux.org/oldlinux/viewthread.php?tid=12182
http://www.oldlinux.org/oldlinux/viewthread.php?tid=14683
//调用show_task，打印所有非空进程的信息
void show_state(void)
{
int i;
printk("\rTask-info:\n\r");
for (i=0;i<NR_TASKS;i++)
if (task[i])//扫描task数组，非空即打印对应task[i]进程相关信息
show_task(i,task[i]);
}
在内核中的调度程序用于选择系统中下一个要运行的进程。这种选择运行机制是多任务操作系统的基础。调度程序可以看作为处于运行状态都进程之间分配CPU运行时间的管理代码。Linux进程是抢占式的，但被抢占的进程仍处于TASK_RUNNING状态，只是暂时没有被CPU运行。进程的抢占发生在进程处于用于态执行阶段，在内核态执行时是不能被强制的。(0.12的不可以，貌似现在的可以了)
schdule()函数首先扫描任务数组，通过比较每个就绪状态任务的运行时间递减滴答计数counter的值来确定当前哪个进程运行的时间最少，哪个counter值最大，就表示运行时间还不长，于是就选中该进程，并使用任务切换宏函数到该进程运行。
void schedule(void)
{
int i,next,c;
struct task_struct ** p;
/* check alarm, wake up any interruptible tasks that have got a signal */
for(p = &LAST_TASK ; p > &FIRST_TASK ; --p)//把p初始化为指向最后一个进程的地址的指针,逆向扫描所有进程
if (*p) {//*p 指向当前进程的指针
if ((*p)->timeout && (*p)->timeout < jiffies) {//这里< 没错，我一直很纠结为什么不是> 这里jiffies是渐变的，持续变的，而timeout 只是作为一个阈值
(*p)->timeout = 0;
//如果当前进程等待很久了((*p)->timeout < jiffies)，并且这个进程处于TASK_INTERRUPTIBLE
//我们就把这个进程置与TASK_RUNNING状态
if ((*p)->state == TASK_INTERRUPTIBLE)
(*p)->state = TASK_RUNNING;
}
if ((*p)->alarm && (*p)->alarm < jiffies) { //如果此时jiffies大于alarm信号周期，则让将SIGALRM写入进程的信号位
(*p)->signal |= (1<<(SIGALRM-1));
(*p)->alarm = 0;
}
if (((*p)->signal & ~(_BLOCKABLE & (*p)->blocked)) &&
(*p)->state==TASK_INTERRUPTIBLE)// 除SIGKILL SIGSTOP信号外，其他信号都是非阻塞状态的话，并且进程处于TASK_INTERRUPTIBLE
(*p)->state=TASK_RUNNING;//我们就把这个进程置与TASK_RUNNING状态
}
/* this is the scheduler proper: */
while (1) {
c = -1;
next = 0;
i = NR_TASKS;
p = &task[NR_TASKS];
while (--i) {//把所有进程都扫一遍，counter是递减的，找出counter最大的进程，保存在next里面
if (!*--p)//当前*p指向进程为空，下一个
continue;
if ((*p)->state == TASK_RUNNING && (*p)->counter > c)
//counter是任务运行时间计数，注意处于scheduled状态的进程也是在运行是，只是没有使用CPU而已
c = (*p)->counter, next = i;
}
if (c) break;//c>0 就说明找到了已经运行一段时间，并且运行时间最短的进程，跳出while(1)
for(p = &LAST_TASK ; p > &FIRST_TASK ; --p)//如果c==0，说明所有schedule的进程都没有运行
if (*p)
(*p)->counter = ((*p)->counter >> 1) +
(*p)->priority; //重新计算counter = counter/2 + priority
}
switch_to(next);//让进程next使用CPU
}
每当选择出一个新的可以运行的进程时，switch_to()宏执行实际进程切换操作。该宏会把CPU的当前进程状态(context)切换成新进程的状态。
在切换之前，switch_to首先检查要切换的进程是否就是当前进程。如果是，啥也别做，直接退出。如果不是，就把内核全局变量current置为新任务的指针。然后ljmp 长跳转到新任务的状态段TSS组成的地址处，造成CPU执行任务切换操作。此时，CPU会把其所有寄存器的状态保存到当前任务寄存器TR中TSS段选择所指向的当前进程任务数据结构，然后把新任务状态段选择符所指向的新任务数据结构tss结构中的寄存器恢复到CPU中，系统正式开始运行新切换的任务。
#define switch_to(n) {struct {long a,b;} __tmp; __asm__("cmpl %%ecx,_current\n\t" \ //进程n是当前current进程，直接结束switch，否则继续je之后的内容
"je 1f\n\t" "movw %%dx,%1\n\t" \ //将新任务的TSS的16选择符号存入 _tmp.b 中
"xchgl %%ecx,_current\n\t" \ //交换ecx 和current的值，这个时候current就是next指向的进程了！
"ljmp %0\n\t" \ // long jump 把控制流跳转到 %0 _tmp 处 这个long jump比较“特别”，一句两句注释说不清楚，
//可能看到这里会疑惑都跳转了，下面的语句还有什么用？有用！因为会“跳回来”
"cmpl %%ecx,_last_task_used_math\n\t" \ // 原任务是否使用过协处理器
"jne 1f\n\t" \//没用过，跳到l，结束
"clts\n" \//用过，清理
"1:" \ //切换TS标识
::"m" (*&__tmp.a),"m" (*&__tmp.b), "d" (_TSS(n)),"c" ((long) task[n])); }
为什么会执行这句话
cmpl %%ecx,_last_task_used_mathhttp://www.oldlinux.org/oldlinux/archiver/?tid-5390.html
int sys_pause(void) //把当前进程转换成可中断的等待状态，并重新调度
{
current->state = TASK_INTERRUPTIBLE;
schedule();
return 0;
}
static inline void __sleep_on(struct task_struct **p, int state)
//看的时候一定要记住，这个_sleep_on 的作用就是把当前进程正等待资源响应或者不在内存时先让他schedule一下，
//让别的程序先运行一段时间的，
//等到自己等待的资源响应之后，这个时候才跳过if判断，执行后面的语句
{
struct task_struct *tmp;
if (!p)//常规检查p 为0的时候直接返回
return;
if (current == &(init_task.task)) //如果当前进程是
panic("task[0] trying to sleep");
tmp = *p;// tmp 指向原等待队列的头指针
*p = current; //*p 指向等待队列的头指针，把current放入等待队列
current->state = state;
repeat: schedule();
if (*p && *p != current) {
//如果*p是 等待队列的头指针，不进入，否则goto一直重复schedule，直到当前current进程是*p
(**p).state = 0;
current->state = TASK_UNINTERRUPTIBLE;
goto repeat;
}
if (!*p)
printk("Warning: *P = NULL\n\r");
if (*p = tmp) // 恢复原来的等待队列，*p 指向原来的等待队列头，逐出current进程
tmp->state=0; //TASK_RUNNING
}
void interruptible_sleep_on(struct task_struct **p) //可中断睡眠
{
__sleep_on(p,TASK_INTERRUPTIBLE);
}
void sleep_on(struct task_struct **p)//不可中断睡眠
{
__sleep_on(p,TASK_UNINTERRUPTIBLE);
}
void wake_up(struct task_struct **p)//唤醒进程
{
if (p && *p) {
if ((**p).state == TASK_STOPPED)
printk("wake_up: TASK_STOPPED");
if ((**p).state == TASK_ZOMBIE)
printk("wake_up: TASK_ZOMBIE");
(**p).state=0; //TASK_RUNNING
}
}
int sys_getpid(void) //各种系统调用查看进程相关信息
{
return current->pid;
}
int sys_getppid(void)
{
return current->p_pptr->pid;
}
int sys_getuid(void)
{
return current->uid;
}
int sys_geteuid(void)
{
return current->euid;
}
int sys_getgid(void)
{
return current->gid;
}
int sys_getegid(void)
{
return current->egid;
}
int sys_nice(long increment)
{
if(current->priority-increment>0)
current->priority -=increment;
return 0;
}
void sched_init(void)//schedule 的初始化 被main.c 调用，真心之只能大概看懂，很多初始化设置不知道为什么
{
int i;
struct desc_struct * p;
if (sizeof(struct sigaction) !=16)
panic("Struct sigactionMUST be 16 bytes");
set_tss_desc(gdt+FIRST_TSS_ENTRY,&(init_task.task.tss));
set_ldt_desc(gdt+FIRST_LDT_ENTRY,&(init_task.task.ldt));
p = gdt+2+FIRST_TSS_ENTRY;
for(i=1;i<NR_TASKS;i++) {
//从1开始，跳过了进程init，保护好刚已经设置好的init_task
//任务清零，描述符清零
task[i] = NULL;
p->a=p->b=0; //偏址清零
p++;
p->a=p->b=0; //TSS 清零
p++;
}
/* Clear NT, so that we won‘t have troubles with that later on */ //从这里我就不知道发生鸟神马。。。T-T
__asm__("pushfl ; andl$0xffffbfff,(%esp) ; popfl");
ltr(0);
lldt(0);
outb_p(0x36,0x43); /* binary, mode 3, LSB/MSB, ch 0 */
outb_p(LATCH & 0xff , 0x40); /* LSB */
outb(LATCH >> 8 , 0x40); /* MSB */
set_intr_gate(0x20,&timer_interrupt);
outb(inb_p(0x21)&~0x01,0x21);
set_system_gate(0x80,&system_call);
}
《linux 内核完全剖析》sched.c sched.h 代码分析笔记,布布扣,bubuko.com
《linux 内核完全剖析》sched.c sched.h 代码分析笔记
原文：http://blog.csdn.net/cinmyheart/article/details/25129835
