进程的切换和系统的一般执行过程【转】

    nice 
    getpriority
    sched_getscheduler/sched_setscheduler
    sched_getparam/sched_setparam
    sched_yield
    sched_get_priority_min/sched_get_priority_max
    sched_rr_get_interval

31#define switch_to(prev, next, last)                    
32do {                                 
33  /*                              
34   * Context-switching clobbers all registers, so we clobber  
35   * them explicitly, via unused output variables.     
36   * (EAX and EBP is not listed because EBP is saved/restored  
37   * explicitly for wchan access and EAX is the return value of   
38   * __switch_to())                     
39   */                                
40  unsigned long ebx, ecx, edx, esi, edi;                
41                                  
42  asm volatile("pushfl\n\t"      /* save    flags */          //保存当前进程的flags
43           "pushl %%ebp\n\t"        /* save    EBP   */       //把当前进程的堆栈基址压栈
44           "movl %%esp,%[prev_sp]\n\t"  /* save    ESP   */   //把当前的栈顶保存到prev->thread.sp
45           "movl %[next_sp],%%esp\n\t"  /* restore ESP   */   //把下一个进程的栈顶保存到esp中，这两句完成了内核堆栈的切换
46           "movl $1f,%[prev_ip]\n\t"    /* save    EIP   */   //保存当前进程的EIP，可以从这恢复
47           "pushl %[next_ip]\n\t"   /* restore EIP   */       //把下一个进程的起点位置压到堆栈，就是next进程的栈顶。next_ip一般是$1f，对于新创建的子进程是ret_from_fork
             //一般用return直接把next_ip pop出来
48           __switch_canary                   
49           "jmp __switch_to\n"  /* regparm call  */  //jmp通过寄存器传递参数，即后面的a,d。 函数__switch_to也有return把next_ip pop出来     
50           "1:\t"              //认为从这开始执行next进程（EIP角度），第一条指令是next_ip这个起点，但前面已经完成内核堆栈的切换，早就是next进程的内核堆栈（算prev进程，比较模糊）          
51           "popl %%ebp\n\t"     /* restore EBP   */  //next进程曾经是prev进程，压栈过ebp  
52           "popfl\n"         /* restore flags */  
53                                  
54           /* output parameters */                
55           : [prev_sp] "=m" (prev->thread.sp),     //当前进程的，在中断内部，在内核态，sp是内核堆栈的栈顶
56             [prev_ip] "=m" (prev->thread.ip),     //当前进程的EIP  
57             "=a" (last),                 
58                                  
59             /* clobbered output registers: */     
60             "=b" (ebx), "=c" (ecx), "=d" (edx),      
61             "=S" (esi), "=D" (edi)             
62                                       
63             __switch_canary_oparam                
64                                  
65             /* input parameters: */                
66           : [next_sp]  "m" (next->thread.sp),    //下一个进程的内核堆栈的栈顶     
67             [next_ip]  "m" (next->thread.ip),    //下一个进程的执行起点
68                                       
69             /* regparm parameters for __switch_to(): */  
70             [prev]     "a" (prev),               //寄存器的传递 
71             [next]     "d" (next)               
72                                  
73             __switch_canary_iparam                
74                                  
75           : /* reloaded segment registers */           
76          "memory");                  
77} while (0)