简单的时间片轮换Linux内核分析
Linux内核操作系统
by干宇宙飞行
原创作品转载请注明出处《Linux内核分析》 MOOC课程
实验环境： window S10专业虚拟盒5.14下Ubuntu 15.10 64第64位
采用快乐煎鸡蛋老师提供的mykernel环境
环境截图
mypcb.h代码
/* my kernel-- simplesimulationofthelinuxosprocessschedule
*
* linux/mykernel/mypcb.h
*
* kernelinternalmy _ timer _ handler
*
*版权(c ) 2013孟宁
*
*修改2014云全张
*
*
* youcanredistributeormodifythisprogramundertheterms
* ofthegnugeneralpubliclicenseaspublishedby
* the自由软件基础设施。
*
* youshouldhavereceivedacopyofthegnugeneralpubliclicense
* along with this program. If not，see。
*/
# definemax _ task _ num 10//maxnumoftaskinsystem
#defineKERNEL_STACK_SIZE1024*8
# define priority _ max 30//priorityrangefrom0to 30
/* CPU-specificstateofthistask * /
结构趋势{
无符号长整型； //point to cpu run address
无符号长sp； //pointtothethreadstack ' stop address
//todoaddotherattrubteofsystemthread
(；
//PCB结构
typedefstructPCB{
intpid； //pcb id
volatilelongstate； /* -1 unrunnable，0 runnable，0 stopped */
charstack[KERNEL_STACK_SIZE]； //each PCB堆叠大小is 1024 * 8
/* CPU-specificstateofthistask * /
structThreadthread；
统一长任务_入口； //thetaskexecuteentrymemoryaddress
结构PCB *下一步； //pcb is a circular linked list
无符号长优先级；//任务优先级
//todoaddotherattrubteofprocesscontrolblock
}tPCB；
//voidmy_schedule(intPID )；
voidmy_schedule(void )；
先看看mypcb.h里有什么
在thread中，ip、sp分别为eip和esp
PCBpid进程id
state进程状态-1就绪0就绪
stack定义了内核堆栈
真红
task_entry
自己类型的指针
定义了调度程序
my_schedule
mymain.c代码
/*
* linux/mykernel/mymain.c
*
* Kernel internal my_start_kernel
*
*版权(c ) 2013孟宁
*
*/
#包含
#包含
#包含
#包含
#包含
#include'mypcb.h '
tPCB task[MAX_TASK_NUM];
tPCB*my_current_task=NULL;
volatileintmy_need_sched=0;//是否需要调度
voidmy_process(void);
void__init my_start_kernel(void)
{
intpid=0;
inti;
/* Initialize process 0*/
task[pid].pid=pid;
task[pid].state=0;/* -1 unrunnable, 0 runnable, >0 stopped */
task[pid].task_entry=task[pid].thread.ip=(unsignedlong)my_process;
task[pid].thread.sp=(unsignedlong)&task[pid].stack[KERNEL_STACK_SIZE-1];
task[pid].next=&task[pid];
/*fork more process */
for(i=1;i
{
memcpy(&task[i],&task[0],sizeof(tPCB));
task[i].pid=i;
task[i].state=-1;
task[i].thread.sp=(unsignedlong)&task[i].stack[KERNEL_STACK_SIZE-1];
task[i].next=task[i-1].next;
task[i-1].next=&task[i];
}
/* start process 0 by task[0] */
pid=0;
my_current_task=&task[pid];
asmvolatile(
"movl %1,%%espnt"/* set task[pid].thread.sp to esp */
"pushl %1nt"/* push ebp */
"pushl %0nt"/* push task[pid].thread.ip */
"retnt"/* pop task[pid].thread.ip to eip */
"popl %%ebpnt"
:
:"c"(task[pid].thread.ip),"d"(task[pid].thread.sp)/* input c or d mean %ecx/%edx*/
);
}
voidmy_process(void)
{
inti=0;
while(1)
{
i++;
if(i%10000000==0)
{
printk(KERN_NOTICE"this is process %d -n",my_current_task->pid);
if(my_need_sched==1)
{
my_need_sched=0;
my_schedule();
}
printk(KERN_NOTICE"this is process %d +n",my_current_task->pid);
}
}
}
先把mypcb.h包含进来
先声明一个task的数组
当前的task的指针
声明一个标志 my_need_sched
my_start_kernel
零号进程初始化
状态就绪
起点、入口是my_process
即函数执行的是my_process
堆栈的栈顶，定义了一个stack
指针指向它自己，因为系统只有它自己。
将零号进程的状态，复制过来
每个进程有它自己的堆栈
新fork的进程添加到这个task链表的尾部
开始执行零号进程
有一段汇编代码，比较关键
asmvolatile(
"movl %1,%%espnt"/* set task[pid].thread.sp to esp */
"pushl %1nt"/* push ebp */
"pushl %0nt"/* push task[pid].thread.ip */
"retnt"/* pop task[pid].thread.ip to eip */
"popl %%ebpnt"
:
:"c"(task[pid].thread.ip),"d"(task[pid].thread.sp)/* input c or d mean %ecx/%edx*/
);
ret之后0号进程启动起来
下面我们来看一下my_process的代码
执行一千万次，之后主动调度
myinterrupt.c
/*
* linux/mykernel/myinterrupt.c
*
* Kernel internal my_timer_handler
*
* Copyright (C) 2013 Mengning
*
*/
#include
#include
#include
#include
#include
#include"mypcb.h"
externtPCB task[MAX_TASK_NUM];
externtPCB*my_current_task;
externvolatileintmy_need_sched;
volatileinttime_count=0;
/*
* Called by timer interrupt.
* it runs in the name of current running process,
* so it use kernel stack of current running process
*/
voidmy_timer_handler(void)
{
#if 1
if(time_count%100==0&&my_need_sched!=1)
{
printk(KERN_NOTICE">>>my_timer_handler here<<
my_need_sched=1;
}
time_count++;
#endif
return;
}
voidmy_schedule(void)
{
tPCB*next;
tPCB*prev;
if(my_current_task==NULL
||my_current_task->next==NULL)
{
return;
}
printk(KERN_NOTICE">>>my_schedule<<
/* schedule */
next=my_current_task->next;
prev=my_current_task;
if(next->state==0)/* -1 unrunnable, 0 runnable, >0 stopped */
{
/* switch to next process */
asmvolatile(
"pushl %%ebpnt"/* save ebp */
"movl %%esp,%0nt"/* save esp */
"movl %2,%%espnt"/* restore esp */
"movl $1f,%1nt"/* save eip */
"pushl %3nt"
"retnt"/* restore eip */
"1:t"/* next process start here */
"popl %%ebpnt"
:"=m"(prev->thread.sp),"=m"(prev->thread.ip)
:"m"(next->thread.sp),"m"(next->thread.ip)
);
my_current_task=next;
printk(KERN_NOTICE">>>switch %d to %d<<pid,next->pid);
}
else
{
next->state=0;
my_current_task=next;
printk(KERN_NOTICE">>>switch %d to %d<<pid,next->pid);
/* switch to new process */
asmvolatile(
"pushl %%ebpnt"/* save ebp */
"movl %%esp,%0nt"/* save esp */
"movl %2,%%espnt"/* restore esp */
"movl %2,%%ebpnt"/* restore ebp */
"movl $1f,%1nt"/* save eip */
"pushl %3nt"
"retnt"/* restore eip */
:"=m"(prev->thread.sp),"=m"(prev->thread.ip)
:"m"(next->thread.sp),"m"(next->thread.ip)
);
}
return;
}
再来看myinterrupt的代码
全局变量声明三个变量
定义时间片 time_count
my_timer_handler中
当调度过一次之后，把my_need_sched赋为1
然后来看my_schedule的函数
前面链表相关的操作和检查
下面if 检查是否就绪
然后进行上下文切换。