sched.c

1017阅读 0评论2009-08-03 jhluroom
分类:LINUX

/*
 * linux/kernel/sched.c
 *
 * (C) 1991 Linus Torvalds
 */


/*
 * 'sched.c' is the main kernel file. It contains scheduling primitives
 * (sleep_on, wakeup, schedule etc) as well as a number of simple system
 * call functions (type getpid(), which just extracts a field from
 * current-task
 */

#include <linux/sched.h>
#include <linux/kernel.h>
#include <linux/sys.h>
#include <linux/fdreg.h>
#include <asm/system.h>
#include <asm/io.h>
#include <asm/segment.h>

#include <signal.h>

#define _S(nr) (1<<((nr)-1))//取信号nr在信号位图上对应的二进制位图

#define _BLOCKABLE (~(_S(SIGKILL) | _S(SIGSTOP)))//除了SIGKILL和SIGSTOP两个信号外,都可以阻塞


void show_task(int nr,struct task_struct * p)//显示任务nr的进程号、进程状态、内核堆栈空闲字节数

    int i,j = 4096-sizeof(struct task_struct);//总的为4K,


    printk("%d: pid=%d, state=%d, ",nr,p->pid,p->state);
    i=0;
    while (i<j && !((char *)(p+1))[i])
        i++;
    printk("%d (of %d) chars free in kernel stack\n\r",i,j);
}

void show_stat(void)//显示每个任务的相关信息

{
    int i;

    for (i=0;i<NR_TASKS;i++)//NR_TASKS=64

        if (task[i])
            show_task(i,task[i]);
}

#define LATCH (1193180/HZ)//PC机的8253定时芯片输入时钟频率为1.193180MHZ,中断的频率为100HZ,也就是10ms发出一次时钟中断。


extern void mem_use(void);

extern int timer_interrupt(void);//时钟中断函数,/kernel/system_call.s

extern int system_call(void);//系统调用函数,/kernel/system_call.s


union task_union {
    struct task_struct task;
    char stack[PAGE_SIZE]//PAGE_SIZE=4096

};//任务的内核态椎栈结构


static union task_union init_task = {INIT_TASK,};//初始任务数据


long volatile jiffies=0;
long startup_time=0;//开机时间

struct task_struct *current = &(init_task.task);//当前任务指针

struct task_struct *last_task_used_math = NULL;//协处理器指针


struct task_struct * task[NR_TASKS] = {&(init_task.task), };//任务指针数组


long user_stack [ PAGE_SIZE>>2 ] ;//用户栈,大小为(4K>>2) =1K


struct {
    long * a;
    short b;
    } stack_start = { & user_stack [PAGE_SIZE>>2] , 0x10 };
/*
 * 'math_state_restore()' saves the current math information in the,将当前协处理器上的内容,保存在老的处理器上,
 * old math state array, and gets the new ones from the current task,并将当前任务协处理器上的内容 加载到协处理器上
 */

void math_state_restore()
{
    if (last_task_used_math == current)
        return;
    __asm__("fwait");
    if (last_task_used_math) {
        __asm__("fnsave %0"::"m" (last_task_used_math->tss.i387));
    }
    last_task_used_math=current;
    if (current->used_math) {
        __asm__("frstor %0"::"m" (current->tss.i387));
    } else {
        __asm__("fninit"::);
        current->used_math=1;
    }
}

/*
 * 'schedule()' is the scheduler function. This is GOOD CODE! There
 * probably won't be any reason to change this, as it should work well
 * in all circumstances (ie gives IO-bound processes good response etc).
 * The one thing you might take a look at is the signal-handler code here.
 *
 * NOTE!! Task 0 is the 'idle' task, which gets called when no other
 * tasks can run. It can not be killed, and it cannot sleep. The 'state'
 * information in task[0] is never used.
 */

void schedule(void)//调度函数

{
    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)//#define LAST_TASK task[NR_TASKS-1],#define FIRST_TASK task[0]

        if (*p) {
            if ((*p)->alarm && (*p)->alarm < jiffies) {//P->alarm,报警定时值,滴答数)

                    (*p)->signal |= (1<<(SIGALRM-1));//对应任务置信号

                    (*p)->alarm = 0;
                }
            if (((*p)->signal & ~(_BLOCKABLE & (*p)->blocked)) &&//p->blocked,进程号屏蔽

            (*p)->state==TASK_INTERRUPTIBLE)//p->state,任务状态

                (*p)->state=TASK_RUNNING;
        }

/* this is the scheduler proper:,调度的主要部分 */

    while (1) {
        c = -1;
        next = 0;
        i = NR_TASKS;
        p = &task[NR_TASKS];
        while (--i) {
            if (!*--p)
                continue;
            if ((*p)->state == TASK_RUNNING && (*p)->counter > c)//p->counter,任务运行时间计数(滴答数,递减的),时间片

                c = (*p)->counter, next = i;
        }//next指向counter值最大,运行时间不长的那个任务

        if (c) break;//当c不为0时,说时当前还有任务的时间片没有用完,进行任务切换于141行,C=-1,NEXT=0时,说明没有一个可运行的任务,进行任务切换。

        for(p = &LAST_TASK ; p > &FIRST_TASK ; --p)//更换每一个任务的counter值

            if (*p)
                (*p)->counter = ((*p)->counter >> 1) +
                        (*p)->priority;
    }
    switch_to(next);//任务切换,当系统中没有其他可运行的任务时,next=0,则去执行任务0,而任务0去执行pause()系统调用,而在pause系统调用中,又调用了schedule()本函数。

}

int sys_pause(void)//转变当前任务的壮态为可中断的等待状态,并重新调度。本函数将使进程睡眼,直到接收到一个信号,执行完进程的操作后,才可本函数返回

{
    current->state = TASK_INTERRUPTIBLE;
    schedule();
    return 0;
}

//将当前任务置为不可中断的等待状态,并将此放入睡眼队列P中,(是否将当前任务插入睡眼队列头指针后呢???

void sleep_on(struct task_struct **p)//P为等待任务队列头指针

{
    struct task_struct *tmp;

    if (!p)
        return;
    if (current == &(init_task.task))//当前任务为0时,

        panic("task[0] trying to sleep");
    tmp = *p;
    *p = current;//将当前任务插入到等待队列P中。

    current->state = TASK_UNINTERRUPTIBLE;
    schedule();
    if (tmp)//只有当这个等待任务被唤醒,调度程序才会返回到这里。

        tmp->state=0;
}
//将当前任务置为可中断的等待状态,并将此放入等待队列P中,原理同前

void interruptible_sleep_on(struct task_struct **p)
{
    struct task_struct *tmp;

    if (!p)
        return;
    if (current == &(init_task.task))
        panic("task[0] trying to sleep");
    tmp=*p;
    *p=current;
repeat:    current->state = TASK_INTERRUPTIBLE;
    schedule();
    if (*p && *p != current) {
        (**p).state=0;
        goto repeat;
    }
    *p=NULL;
    if (tmp)
        tmp->state=0;
}

void wake_up(struct task_struct **p)//唤醒*p所指向的任务。*p为任务等待队列头指针,由于新等待任务是插入等待队列头指针处的,因此唤醒的是最后进入等待队列的任务。

{
    if (p && *p) {
        (**p).state=0;//置为就绪状态(TASK_RUNNINT)

        *p=NULL;
    }
}

/*
 * OK, here are some floppy things that shouldn't be in the kernel
 * proper. They are here because the floppy needs a timer, and this
 * was the easiest way of doing it.
 */

static struct task_struct * wait_motor[4] = {NULL,NULL,NULL,NULL};
static int mon_timer[4]={0,0,0,0};
static int moff_timer[4]={0,0,0,0};
unsigned char current_DOR = 0x0C;

int ticks_to_floppy_on(unsigned int nr)
{
    extern unsigned char selected;
    unsigned char mask = 0x10 << nr;

    if (nr>3)
        panic("floppy_on: nr>3");
    moff_timer[nr]=10000;        /* 100 s = very big :-) */
    cli();                /* use floppy_off to turn it off */
    mask |= current_DOR;
    if (!selected) {
        mask &= 0xFC;
        mask |= nr;
    }
    if (mask != current_DOR) {
        outb(mask,FD_DOR);
        if ((mask ^ current_DOR) & 0xf0)
            mon_timer[nr] = HZ/2;
        else if (mon_timer[nr] < 2)
            mon_timer[nr] = 2;
        current_DOR = mask;
    }
    sti();
    return mon_timer[nr];
}

void floppy_on(unsigned int nr)
{
    cli();
    while (ticks_to_floppy_on(nr))
        sleep_on(nr+wait_motor);
    sti();
}

void floppy_off(unsigned int nr)
{
    moff_timer[nr]=3*HZ;
}

void do_floppy_timer(void)
{
    int i;
    unsigned char mask = 0x10;

    for (i=0 ; i<4 ; i++,mask <<= 1) {
        if (!(mask & current_DOR))
            continue;
        if (mon_timer[i]) {
            if (!--mon_timer[i])
                wake_up(i+wait_motor);
        } else if (!moff_timer[i]) {
            current_DOR &= ~mask;
            outb(current_DOR,FD_DOR);
        } else
            moff_timer[i]--;
    }
}

#define TIME_REQUESTS 64//最多64个定时器

    
static struct timer_list {//定时器链表结构,循环链表,可以将next_time看作这个链表的头,所指向的就为第一个定时器

    long jiffies;//定时滴答数

    void (*fn)();//定时处理函数

    struct timer_list * next;
} timer_list[TIME_REQUESTS], * next_timer = NULL;

void add_timer(long jiffies, void (*fn)(void))//添加定是器

{
    struct timer_list * p;

    if (!fn)
        return;
    cli();//禁止中断

    if (jiffies <= 0)
        (fn)();
    else {
        for (p = timer_list ; p < timer_list + TIME_REQUESTS ; p++)
            if (!p->fn)
                break;//找出空的一项

        if (p >= timer_list + TIME_REQUESTS)
            panic("No more time requests free");
        p->fn = fn;
        p->jiffies = jiffies;
        p->next = next_timer;
        next_timer = p;
        while (p->next && p->next->jiffies < p->jiffies) {//链表按定时值从小到大排列

            p->jiffies -= p->next->jiffies;
            fn = p->fn;
            p->fn = p->next->fn;
            p->next->fn = fn;
            jiffies = p->jiffies;
            p->jiffies = p->next->jiffies;
            p->next->jiffies = jiffies;
            p = p->next;
        }
    }
    sti();//开启中断

}

void do_timer(long cpl)//时钟中断C函数处理程序,system_call.s line 176 _timer_interupter 调用此函数,参数cpl 为 当前特权级0(发生时正执行内核代码)或3(当前发生时正执行用户代码 )

{
    extern int beepcount;//扬声器发声时间滴答数linux-0.11\chr_drv\console.c line 697

    extern void sysbeepstop(void);//关闭扬声器linux-0.11\kernel\chr_drv\console.c line 691


    if (beepcount)
        if (!--beepcount)
            sysbeepstop();

    if (cpl)
        current->utime++;//cpl=3

    else
        current->stime++;//cpl=0    


    if (next_timer) {
        next_timer->jiffies--;//定时器链表是按定时值的大小从小到大排列的

        while (next_timer && next_timer->jiffies <= 0) {//定时时间到,则将本定时器移除掉,并将执行相应的定时函数

            void (*fn)(void);
            
            fn = next_timer->fn;
            next_timer->fn = NULL;
            next_timer = next_timer->next;
            (fn)();
        }
    }
    if (current_DOR & 0xf0)
        do_floppy_timer();
    if ((--current->counter)>0) return;//当前进程任务运行时间还没有完,则返回

    current->counter=0;//否则,将当前任务运行时间设为0

    if (!cpl) return;//如果运行于内核态(cpl=0)则返回,内核态的程序不信赖于counter的人值进行调度。

    schedule();//进行任务调度,

}

int sys_alarm(long seconds)//设定当前任务报警定时时间值

{
    int old = current->alarm;

    if (old)
        old = (old - jiffies) / HZ;
    current->alarm = (seconds>0)?(jiffies+HZ*seconds):0;
    return (old);
}

int sys_getpid(void)//取进程 号

{
    return current->pid;
}

int sys_getppid(void)//取父进程号

{
    return current->father;
}

int sys_getuid(void)//取用户号

{
    return current->uid;
}

int sys_geteuid(void)//取有效用户号

{
    return current->euid;
}

int sys_getgid(void)//取组号

{
    return current->gid;
}

int sys_getegid(void)//取有效组号

{
    return current->egid;
}

int sys_nice(long increment)//降低对CPU的优先使用权

{
    if (current->priority-increment>0)
        current->priority -= increment;
    return 0;
}

void sched_init(void)//内核调度程序 的初始化子程序,由main()函数调用

{
    int i;
    struct desc_struct * p;

    if (sizeof(struct sigaction) != 16)
        panic("Struct sigaction MUST 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++) {
        task[i] = NULL;
        p->a=p->b=0;
        p++;
        p->a=p->b=0;
        p++;
    }
/* Clear NT, so that we won't have troubles with that later on */
    __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);
}

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