把握linux内核设计（五）：下半部机制之工作队列及几种机制的选择

# ps x | grep event | grep -v grep
    9 ?        S      0:00 [events/0]
   10 ?        S      0:00 [events/1]

struct workqueue_struct {
    struct cpu_workqueue_struct *cpu_wq;    //该数组每一项对应系统中的一个处理器
    struct list_head list;
    const char *name;
    int singlethread;
    int freezeable;     /* Freeze threads during suspend */
    int rt;
#ifdef CONFIG_LOCKDEP
    struct lockdep_map lockdep_map;
#endif
}

struct cpu_workqueue_struct {

    spinlock_t lock;    //保护该结构

    struct list_head worklist;    //工作列表
    wait_queue_head_t more_work;    //等待队列，其中的工作者线程因等待而处于睡眠状态
    struct work_struct *current_work;

    struct workqueue_struct *wq;    //关联工作队列结构
    struct task_struct *thread;    // 关联线程,指向结构中工作者线程的进程描述符指针
} ____cacheline_aligned;

struct work_struct {                                                                                                                                    
    atomic_long_t data;
......
    struct list_head entry;//连接所有链表
    work_func_t func;
.....
};

static int worker_thread(void *__cwq)
{
    struct cpu_workqueue_struct *cwq = __cwq;
    DEFINE_WAIT(wait);

    if (cwq->wq->freezeable)
        set_freezable();

    for (;;) {
    //线程将自己设置为休眠状态并把自己加入等待队列
        prepare_to_wait(&cwq->more_work, &wait, TASK_INTERRUPTIBLE);
        if (!freezing(current) &&
            !kthread_should_stop() &&
            list_empty(&cwq->worklist))
            schedule();//如果工作对列是空的，线程调用schedule()函数进入睡眠状态
        finish_wait(&cwq->more_work, &wait);

        try_to_freeze();

//如果链表有对象，线程就将自己设为运行态，脱离等待队列
        if (kthread_should_stop())
            break;

//再次调用run_workqueue()执行推后的工作
        run_workqueue(cwq);
    }

    return 0;
}

static void run_workqueue(struct cpu_workqueue_struct *cwq) 
{
    spin_lock_irq(&cwq->lock);
    while (!list_empty(&cwq->worklist)) {
        //链表不为空时，选取下一个节点对象
        struct work_struct *work = list_entry(cwq->worklist.next,
                        struct work_struct, entry);
        //获取希望执行的函数func及其参数data
        work_func_t f = work->func;
......
        trace_workqueue_execution(cwq->thread, work);
        cwq->current_work = work;
        //把该结点从链表上解下来
        list_del_init(cwq->worklist.next);
        spin_unlock_irq(&cwq->lock);

        BUG_ON(get_wq_data(work) != cwq);
        //将待处理标志位pending清0
        work_clear_pending(work);
        lock_map_acquire(&cwq->wq->lockdep_map);
        lock_map_acquire(&lockdep_map);
        //执行函数
        f(work);
        lock_map_release(&lockdep_map);
        lock_map_release(&cwq->wq->lockdep_map);

......
        spin_lock_irq(&cwq->lock);
        cwq->current_work = NULL;
    }
    spin_unlock_irq(&cwq->lock);
}

int schedule_work(struct work_struct *work)
{
    return queue_work(keventd_wq, work);
}

int schedule_delayed_work(struct delayed_work *dwork, unsigned long delay)                                             
{
    return queue_delayed_work(keventd_wq, dwork, delay);
}

#include <linux/init.h>
#include <linux/module.h>

#include <linux/workqueue.h> //work_strcut


//struct work_struct      ws;
struct delayed_work     dw;

void workqueue_func(struct work_struct *ws)    //处理函数
{
    printk(KERN_ALERT"Hello, this is shallnet!\n");
}

static int __init kwq_init(void)
{
    printk(KERN_ALERT"===%s===\n", __func__);

    //INIT_WORK(&ws, workqueue_func);    //建需要推后完成的工作
    //schedule_work(&ws);    //调度工作

    INIT_DELAYED_WORK(&dw, workqueue_func);
    schedule_delayed_work(&dw, 10000);

    return 0;
}

static void __exit kwq_exit(void)
{
    printk(KERN_ALERT"===%s===\n", __func__);

    flush_scheduled_work();
}

module_init(kwq_init);
module_exit(kwq_exit);

MODULE_LICENSE("GPL");
MODULE_AUTHOR("shallnet");
MODULE_DESCRIPTION("blog.csdn.net/shallnet");

struct workqueue_struct *create_workqueue(const char *name);

struct workqueue_struct    *keventd_wq；
kevent_wq = create_workqueue("event");

int queue_work(struct workqueue_struct *wq, struct work_struct *work);
int queue_delayed_work(struct workqueue_struct *wq,struct delayed_work *work,unsigned long delay);

#include <linux/init.h>
#include <linux/module.h>
#include <linux/workqueue.h> //work_strcut

struct workqueue_struct *sln_wq = NULL;
//struct work_struct      ws;
struct delayed_work     dw;

void workqueue_func(struct work_struct *ws)
{
    printk(KERN_ALERT"Hello, this is shallnet!\n");
}

static int __init kwq_init(void)
{
    printk(KERN_ALERT"===%s===\n", __func__);

    sln_wq = create_workqueue("sln_wq");    //创建名为sln_wq的工作队列

    //INIT_WORK(&ws, workqueue_func);
    //queue_work(sln_wq, &ws);

    INIT_DELAYED_WORK(&dw, workqueue_func);    //
    queue_delayed_work(sln_wq, &dw, 10000);    //

    return 0;
}

static void __exit kwq_exit(void)
{
    printk(KERN_ALERT"===%s===\n", __func__);

    flush_workqueue(sln_wq);
}

module_init(kwq_init);
module_exit(kwq_exit);

MODULE_LICENSE("GPL");
MODULE_AUTHOR("shallnet");
MODULE_DESCRIPTION("blog.csdn.net/shallnet");

把握linux内核设计（五）：下半部机制之工作队列及几种机制的选择

原文：http://blog.csdn.net/shallnet/article/details/47115055