实验:mykernel时间片轮转多道程序内核
进入实验楼实验,在终端中分别输入以下命令
cd LinuxKernel/linux-3.9.4
rm -rf mykernel
patch -p1 < ../mykernel_for_linux3.9.4sc.patch //打补丁
make allnoconfig
make
qemu -kernel arch/x86/boot/bzImage
make过程如下图:
https://dn-simplecloud.shiyanlou.com/8449831540547871321-wm
https://dn-simplecloud.shiyanlou.com/8449831540548661907-wm
mykernel时间片轮转代码分析
这里主要分析上面实验中改写的三个文件,其作用简述如下,
mypcb.h : 进程控制块PCB结构体定义。
mymain.c: 初始化各个进程并启动0号进程。
myinterrupt.c:时钟中断处理和进程调度算法。
mypcb.h头文件
#define MAX_TASK_NUM 4
#define KERNEL_STACK_SIZE 1024*8
/* CPU-specific state of this task */
struct Thread {
unsigned long ip;
unsigned long sp;
};
typedef struct PCB{
int pid;
volatile long state;
char stack[KERNEL_STACK_SIZE];
/* CPU-specific state of this task */
struct Thread thread;
unsigned long task_entry; //入口
struct PCB *next;
}tPCB;
void my_schedule(void);
在这个文件里,定义了 Thread 结构体,用于存储当前进程中正在执行的线程的ip和sp
这里还有一个函数的声明 my_schedule,它的实现在my_interrupt.c中,在mymain.c中的各个进程函数会根据一个全局变量的状态来决定是否调用它,从而实现主动调度。
mymain.c文件
#include <linux/types.h>
#include <linux/string.h>
#include <linux/ctype.h>
#include <linux/tty.h>
#include <linux/vmalloc.h>
#include "mypcb.h"
tPCB task[MAX_TASK_NUM];
tPCB * my_current_task = NULL;
volatile int my_need_sched = 0;
void my_process(void);
void __init my_start_kernel(void)
{
int pid = 0;
int i;
task[pid].pid = pid;
task[pid].state = 0;/* -1 unrunnable, 0 runnable, >0 stopped */
task[pid].task_entry = task[pid].thread.ip = (unsigned long)my_process;
task[pid].thread.sp = (unsigned long)&task[pid].stack[KERNEL_STACK_SIZE-1];
task[pid].next = &task[pid];
for(i=1;i<MAX_TASK_NUM;i++)
{
memcpy(&task[i],&task[0],sizeof(tPCB));
task[i].pid = i;
task[i].state = -1;
task[i].thread.sp = (unsigned long)&task[i].stack[KERNEL_STACK_SIZE-1];
task[i].next = task[i-1].next;
task[i-1].next = &task[i];
}
pid = 0;
my_current_task = &task[pid];
asm volatile(
"movl %1,%%esp
" /* set task[pid].thread.sp to esp */
"pushl %1
" /* push ebp */
"pushl %0
" /* push task[pid].thread.ip */
"ret
" /* pop task[pid].thread.ip to eip */
"popl %%ebp
"
:
: "c" (task[pid].thread.ip),"d" (task[pid].thread.sp) /* input c or d mean %ecx/%edx*/
);
}
void my_process(void)
{
int i = 0;
while(1)
{
i++;
if(i%10000000 == 0)
{
printk(KERN_NOTICE "this is process %d -
",my_current_task->pid);
if(my_need_sched == 1)
{
my_need_sched = 0;
my_schedule();
}
printk(KERN_NOTICE "this is process %d +
",my_current_task->pid);
}
}
}
这里的函数 my_start_kernel 是系统启动后,最先调用的函数,在这个函数里完成了0号进程的初始化和启动,并创建了其它的进程PCB,以方便后面的调度。在模拟系统里,每个进程的函数代码都是一样的,即 my_process 函数,my_process 在执行的时候,会打印出当前进程的 id,从而使得我们能够看到当前哪个进程正在执行。
另外,在 my_process 也会检查一个全局标志变量 my_need_sched,一旦发现其值为 1 ,就调用 my_schedule 完成进程的调度。
myinterrupt.c文件
#include <linux/types.h>
#include <linux/string.h>
#include <linux/ctype.h>
#include <linux/tty.h>
#include <linux/vmalloc.h>
#include "mypcb.h"
extern tPCB task[MAX_TASK_NUM];
extern tPCB * my_current_task;
extern volatile int my_need_sched;
volatile int time_count = 0;
void my_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;
}
void my_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 */
{
my_current_task = next;
printk(KERN_NOTICE ">>>switch %d to %d<<<
",prev->pid,next->pid);
/* 切换进程 */
asm volatile(
"pushl %%ebp
" /* save ebp */
"movl %%esp,%0
" /* save esp */
"movl %2,%%esp
" /* restore esp */
"movl $1f,%1
" /* save eip */
"pushl %3
"
"ret
" /* restore eip */
"1: " /* next process start here */
"popl %%ebp
"
: "=m" (prev->thread.sp),"=m" (prev->thread.ip)
: "m" (next->thread.sp),"m" (next->thread.ip)
);
}
else
{
next->state = 0;
my_current_task = next;
printk(KERN_NOTICE ">>>switch %d to %d<<<
",prev->pid,next->pid);
/* switch to new process */
asm volatile(
"pushl %%ebp
" /* save ebp */
"movl %%esp,%0
" /* save esp */
"movl %2,%%esp
" /* restore esp */
"movl %2,%%ebp
" /* restore ebp */
"movl $1f,%1
" /* save eip */
"pushl %3
"
"ret
" /* restore eip */
: "=m" (prev->thread.sp),"=m" (prev->thread.ip)
: "m" (next->thread.sp),"m" (next->thread.ip)
);
}
return;
}
通过本讲的学习和实验,我们知道操作系统的核心功能就是:进程调度和中断机制,通过与硬件的配合实现多任务处理,再加上上层应用软件的支持,最终变成可以使用户可以很容易操作的计算机系统。通过这个实验我们可以知道,mykernel系统启动后,调用my_start_kernel函数和my_timer_handler函数,完成系统进程的初始化和进程的轮转调度。