sched.c sched.h 代码分析笔记
首先上header file
sched.h
#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)#endifextern 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
对于_TSS 和 _LDT两个宏定义
#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))
TSS是第五个(IDT是第一个) ,每一个描述符号占8byte ，于是有 FIRST_TSS_ENRTY<<3
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。
show_task
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
show_task
//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。
schedule()
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。
switch_to
#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_math
既然任务切换时CPU会恢复寄存器现场，那么它当然也会保存寄存器现场了。这些寄存器现场都会被写入原任务的tss结构里，值得注意的是，EIP会指向引起任务切换指令ljmp的下一条指令cmpl，所以，很明显，当原任务有朝一日再次被调度运行时，它将从EIP所指的地方，而这个地方恰巧是cmpl !比较有用的一个帖子：
http://www.oldlinux.org/oldlinux/archiver/?tid-5390.html
sys_pause
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;}
__sleep_on
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}
interruptible_sleep_on
void interruptible_sleep_on(struct task_struct **p) //可中断睡眠{ __sleep_on(p,TASK_INTERRUPTIBLE);}
sleep_on
void sleep_on(struct task_struct **p)//不可中断睡眠{ __sleep_on(p,TASK_UNINTERRUPTIBLE);}
wake_up
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 }}
get_pid,getppid,getuid,geteuid,getgid,sys_nice
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;}
sched_init
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);}
而有的旅行是释放负面情绪，换个心情，轻装上阵。
