2018-2019-1 20189221《Linux内核原理与分析》第三周作业

2018-2019-1 20189221《Linux内核原理与分析》第三周作业

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实验二 完成一个简单的时间片轮转多道程序内核代码

实验过程

在实验楼中编译内核

编写mymain.c函数和myinterrupt.c函数实现时间片轮转调用

mymain.c：

myinterrupt.c：

make：

内核实现：

代码分析

代码使用的是《庖丁解牛Linux内核分析》书中代码：

mypcb.h:定义了PCB结构体

#define MAX_TASK_NUM        4
#define KERNEL_STACK_SIZE   1024*8

struct Thread {
    unsigned long       ip
    unsigned long       sp
};

typedef struct PCB
    int pid;
    volatile long state;    /* -1 unrunnable, 0 runnable, >0 stopped */
    char stack[KERNEL_STACK_SIZE];
    struct Thread thread;
    unsigned long   task_entry;
    struct PCB *next;
}tPCB;

void my_schedule(void)

• ip用于eip的保存
• sp用于esp的保存
• pid--> 进程号
• state--> 进程状态
• stack[KERNEL_STACK_SIZE]--> 进程的栈
• Thread Thread--> Thread结构体
• task_entry--> 起始入口地址
• PCB *next-->next指针。

mymain.c:初始化进程，启功0号进程

#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\n\t"
        "pushl %1\n\t"
        "pushl %0\n\t"
        "ret\n\t"
        "popl %%ebp\n\t"
        :
        : "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 -\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);
        }
    }
}

• my_start_kernel作为标志，用来表示是否调度
• 创建的新进程放在进程列表尾部，所有的进程是一个循环链表

myinterrupt.c:产生中断，my_need_sched标志设1，

#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%10000 == 0 && my_need_sched != 1)
    {
        printk(KERN_NOTICE ">>>my_timer_handler here<<<\n");
        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<<<\n");
    /* schedule */
    next = my_current_task->next;
    prev = my_current_task;
    if(next->state == 0)/* -1 unrunnable, 0 runnable, >0 stopped */
    {
        asm volatile(
            "pushl %%ebp\n\t"
            "movl %%esp,%0\n\t"
            "movl %2,%%esp\n\t"
            "movl $1f,%1\n\t"
            "pushl %3\n\t"
            "ret\n\t"
            "1:\t"
            "popl %%ebp\n\t"
            : "=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<<<\n",prev->pid,next->pid);
    }
    else
    {
        next->state = 0;
        my_current_task = next;
        printk(KERN_NOTICE ">>>switch %d to %d<<<\n",prev->pid,next->pid);
        /* switch to new process */
        asm volatile(
            "pushl %%ebp\n\t"
            "movl %%esp,%0\n\t"
            "movl %2,%%esp\n\t"
            "movl %2,%%ebp\n\t"
            "movl $1f,%1\n\t"
            "pushl %3\n\t"
            "ret\n\t"
            : "=m" (prev->thread.sp),"=m" (prev->thread.ip)
            : "m" (next->thread.sp),"m" (next->thread.ip)
        );
    }
    return;
}

• if判断下一个进程是否可运行，执行进程切换

以myinterrupt.c中的asm内嵌汇编程序为例：

"pushl %%ebp"       /* 保存当前ebp */
"movl %%esp,%0"     /* 保存当前esp */
"movl %2,%%esp"     /* 重新记录要跳转进程的esp，%2为 next->thread.sp*/
"movl $1f,%1"       /* 保存当前eip ，%1为prev->thread.ip*/
"pushl %3"
"ret"               /* 记录要跳转进程的eip，%3为 next->thread.ip*/
"1:\t"                  /* 下一个进程开始执行 */
"popl %%ebp"
: "=m" (prev->thread.sp),"=m" (prev->thread.ip)
: "m" (next->thread.sp),"m" (next->thread.ip)

堆栈调用过程：

"pushl %%ebp"       /* 保存当前ebp */
"movl %%esp,%0"     /* 保存当前esp */
"movl %2,%%esp"     /* 重新记录要跳转进程的esp ，%2为 next->thread.sp*/
"movl %2,%%ebp"     /* 重新记录要跳转进程的ebp，%2为 next->thread.sp */
"movl $1f,%1"       /* 保存当前eip ，%1为prev->thread.ip，%1f就是指标号1:的代码在内存中存储的地址*/
"pushl %3"
"ret"               /* 重新记录要跳转进程的eip，%3为 next->thread.ip */
: "=m" (prev->thread.sp),"=m" (prev->thread.ip)
: "m" (next->thread.sp),"m" (next->thread.ip)

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遇到的问题

这周遇到的问题很低级

• Markdown的书写问题，列表中无序列表的嵌套总是会格式不对。
• 想要自己设计代码实现mykernel时间片轮转多道程序，心有不逮，行有不逮
• 这周的学习时间分配不均匀，因为一些客观存在的外部因素和一些主观上的内在因素干扰，学习计划没有很好实施。之后要严格执行自己的计划表。
• 时间片轮转调度是操作系统调度算法的基础组成部分，在此基础上复习其他调度算法，尝试实现一下，参考博客：[浅析Linux内核调度]![]