linux 内核原代码 sched.c 的注释
/*
* '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
#include
#include
#include
#include
#include
#include
#define LATCH (1193180/HZ)
extern void mem_use(void);
extern int timer_interrupt(void);
extern int system_call(void);
union task_union {
struct task_struct task;
char stack[PAGE_SIZE];
};
static union task_union init_task = {INIT_TASK,};
long volatile jiffies=0;
long startup_time=0;
struct task_struct *current = &(init_task.task), *last_task_used_math =
NULL;
struct task_struct * task[NR_TASKS] = {&(init_task.task), };
long user_stack [ PAGE_SIZE>>2 ] ;
struct {
long * a;
short b;
} stack_start = { & user_stack [PAGE_SIZE>>2] , 0x10 };
/*
* 'math_state_restore()' saves the current math information in the
* old math state array, and gets the new ones from the current task
*/
void math_state_restore() @@协处理器状态保存
{
if (last_task_used_math)
__asm__("fnsave %0"::"m" (last_task_used_math->tss.i387));
if (current->used_math)
__asm__("frstor %0"::"m" (current->tss.i387));
else {
__asm__("fninit"::);
current->used_math=1;
}
last_task_used_math=current;
}
/*
* '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)
{
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)
if (*p) {
if ((*p)->alarm && (*p)->alarm signal |= (1alarm = 0;
}
if ((*p)->signal && (*p)->state==TASK_INTERRUPTIBLE)
(*p)->state=TASK_RUNNING;
}
@@ task 1 如何变为TASK_RUNNING??signal 如何得到,alarm如何变非0且state == TASK_RUNNING && (*p)->counter >c)
c = (*p)->counter, next = i;
}
if (c) break; @@记数大于零
for(p = &LAST_TASK ; p >&FIRST_TASK ; --p)
if (*p)
(*p)->counter = ((*p)->counter >>1) +
(*p)->priority;
}
switch_to(next);
}
int sys_pause(void)
{
current->state = TASK_INTERRUPTIBLE; @@任务可中断
schedule();
return 0;
}
void 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;
current->state = TASK_UNINTERRUPTIBLE;
schedule();
if (tmp) @@激活p，什么时候回来？唤醒上次睡眠的进程
tmp->state=0;
}
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;
}
@@好象下不来
*p=NULL;
if (tmp)
tmp->state=0;
}
void wake_up(struct task_struct **p)
{
if (p && *p) {
(**p).state=0; @@唤醒该进程running
*p=NULL; @@睡眠栈为0
}
}
void do_timer(long cpl) @@定时调度
{
if (cpl)
current->utime++; @@用户态时间加一
else
current->stime++; @@系统态时间加一
if ((--current->counter)>0) return; @@当前记数减一
current->counter=0;
if (!cpl) return;
schedule();
}
int sys_alarm(long seconds)
{
current->alarm = (seconds>0)?(jiffies+HZ*seconds):0;
return seconds;
}
int sys_getpid(void)
{
return current->pid;
}
int sys_getppid(void)
{
return current->father;
}
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;
}
int sys_signal(long signal,long addr,long restorer)
{
long i;
switch (signal) {
case SIGHUP: case SIGINT: case SIGQUIT: case SIGILL:
case SIGTRAP: case SIGABRT: case SIGFPE: case SIGUSR1:
case SIGSEGV: case SIGUSR2: case SIGPIPE: case SIGALRM:
case SIGCHLD:
i=(long) current->sig_fn[signal-1];
current->sig_fn[signal-1] = (fn_ptr) addr;
current->sig_restorer = (fn_ptr) restorer;
return i;
default: return -1;
}
}
void sched_init(void)
{
int i;
struct desc_struct * p;
set_tss_desc(gdt+FIRST_TSS_ENTRY,&(init_task.task.tss));@@init task tss
set_ldt_desc(gdt+FIRST_LDT_ENTRY,&(init_task.task.ldt));@@init ldt
p = gdt+2+FIRST_TSS_ENTRY;
for(i=1;ia=p->b=0;
p++;
p->a=p->b=0;
p++;
}
ltr(0); @@调入task 0的tss
lldt(0); @@调入task 0的ldt
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); @@irq 0 时钟中断
outb(inb_p(0x21)&~0x01,0x21);
set_system_gate(0x80,&system_call);
}