linux驱动编程--工作队列浅析

          内核默认为每个cpu创建一个worker process，events/0；并在全局的工作队列上为其挂上了一个专属的链表（）。工作会被挂到该链表上，由events/0取出来执行。centainly, except for this default worker process.User could create a new worker, too. and the kernel will help the new worker create a new workqueue, for mange its work.

工作队列相关函数

//重要结构体struct work_struct;//装载需要处理的事件信息的实体struct workqueue_struct;//全局工作队列头，内核会自动帮助维护一个全局工作队列链表，用户只需要将需要处理的工作挂上去即可struct cpu_workqueue_struct;//与cpu绑定的工作struct delayed_work;//用于有延时的工作//初始化INIT_WORK(_work,_func);INIT_DELAYED_WORK(_work,_func);DECLARE_WORK(n,f);DECLARE_DELAYED_WORK(n,f);//常用函数schedule_work(a);//将一个工作添加到调度列表中schedule_delayed_work(struct delayed_work * dwork,unsigned long delay);cancel_delayed_work(struct delayed_work * work);//取消一个延迟的工作flush_scheduled_work(void);//刷新工作队列，在取消之后建议刷新一遍工作队列create_workqueue(name);//创建一个全局工作队列，并创建其对应的worker processcreate_singlethread_workqueue(name);destroy_workqueue(struct workqueue_struct * wq);//销毁一个工作队列queue_work(struct workqueue_struct * wq,struct work_struct * work);//调度一个"指定"的工作queue_delayed_work(struct workqueue_struct * wq,struct delayed_work * dwork,unsigned long delay);

下面来是相关结构体分析：

 

/** 用来记录工作信息*/struct work_struct {atomic_long_t data;//用户处理函数数据+ ?#define WORK_STRUCT_PENDING 0/* T if work item pending execution */#define WORK_STRUCT_FLAG_MASK (3UL)#define WORK_STRUCT_WQ_DATA_MASK (~WORK_STRUCT_FLAG_MASK)struct list_head entry;  //用来挂到cpu工作队列链表的挂载点，也许在之后会通过container_of(obj,type,memb)找到该实体work_func_t func;       //用户处理函数#ifdef CONFIG_LOCKDEPstruct lockdep_map lockdep_map;#endif         };         /** 用来*/struct workqueue_struct;//全局工作队的结构体，每个cpu有一个events，且在内核的全局工作队列链表上会为其维护一个专属二级链表/* * The externally visible workqueue abstraction is an array of * per-CPU workqueues: */struct workqueue_struct {struct cpu_workqueue_struct *cpu_wq;//每个工作队列绑定一个cpu，其下会记录该cpu需要处理的工作链表struct list_head list;//被用来挂到内核的全局工作队列时用，以container_of()找回const char *name;//该工作队列的名字int singlethread;int freezeable;/* Freeze threads during suspend */int rt;#ifdef CONFIG_LOCKDEPstruct lockdep_map lockdep_map;#endif};struct cpu_workqueue_struct *cpu_wq;/* * The per-CPU workqueue (if single thread, we always use the first * possible cpu). */struct cpu_workqueue_struct {spinlock_t lock;struct list_head worklist;          //当前cpu需要处理的工作wait_queue_head_t more_work;//当cpu没事时，会在该waitqueue上睡眠，在使用时用wakeup()唤醒struct work_struct *current_work;struct workqueue_struct *wq;struct task_struct *thread;} ____cacheline_aligned;

几个重要函数分析：

        schedule_work()是用来像默认工作队列（events）添加工作的。对应的是queue_work()，可以用来向指定工作队列添加工作，例如自己新建的工作队列。

schedule_work(struct work_struct * work);/** * schedule_work - put work task in global workqueue * @work: job to be done * * This puts a job in the kernel-global workqueue. */int schedule_work(struct work_struct *work){return queue_work(keventd_wq, work);//向默认的工作队列中添加一个新工作}/** * queue_work - queue work on a workqueue * @wq: workqueue to use * @work: work to queue * * Returns 0 if @work was already on a queue, non-zero otherwise. * * We queue the work to the CPU on which it was submitted, but if the CPU dies * it can be processed by another CPU. */int queue_work(struct workqueue_struct *wq, struct work_struct *work){int ret;ret = queue_work_on(get_cpu(), wq, work);//把work挂到get_cpu()所指定cpu的wq上去。之后该工作就有该cpu的工作者线程events负责完成put_cpu();//使能抢占return ret;}/** * queue_work_on - queue work on specific cpu * @cpu: CPU number to execute work on * @wq: workqueue to use * @work: work to queue * * Returns 0 if @work was already on a queue, non-zero otherwise. * * We queue the work to a specific CPU, the caller must ensure it * can't go away. */intqueue_work_on(int cpu, struct workqueue_struct *wq, struct work_struct *work){int ret = 0;if (!test_and_set_bit(WORK_STRUCT_PENDING, work_data_bits(work))) {BUG_ON(!list_empty(&work->entry));__queue_work(wq_per_cpu(wq, cpu), work);ret = 1;}return ret;}#define put_cpu()preempt_enable()static void __queue_work(struct cpu_workqueue_struct *cwq, struct work_struct *work){unsigned long flags;spin_lock_irqsave(&cwq->lock, flags);insert_work(cwq, work, &cwq->worklist);spin_unlock_irqrestore(&cwq->lock, flags);}static void insert_work(struct cpu_workqueue_struct *cwq,struct work_struct *work, struct list_head *head){trace_workqueue_insertion(cwq->thread, work);//??set_wq_data(work, cwq);//??/* * Ensure that we get the right work->data if we see the * result of list_add() below, see try_to_grab_pending(). */smp_wmb();//??list_add_tail(&work->entry, head);//把新工作的挂到该cpu的处理队列上去wake_up(&cwq->more_work);//唤醒等待队列的内容}

 

create_workqueue()

        下面是看一下工作者的具体创建过程

#define create_workqueue(name) __create_workqueue((name), 0, 0, 0)#define __create_workqueue(name, singlethread, freezeable, rt)\__create_workqueue_key((name), (singlethread), (freezeable), (rt), \       NULL, NULL)//创建一个新的wq将其挂到内核的全局工作队列上去.(通过list挂)//且初始化该wq，为其指定cpu//该wq下的cwq中会挂具体的工作struct workqueue_struct *__create_workqueue_key(const char *name,int singlethread,int freezeable,int rt,struct lock_class_key *key,const char *lock_name){struct workqueue_struct *wq;struct cpu_workqueue_struct *cwq;int err = 0, cpu;wq = kzalloc(sizeof(*wq), GFP_KERNEL);if (!wq)return NULL;wq->cpu_wq = alloc_percpu(struct cpu_workqueue_struct);if (!wq->cpu_wq) {kfree(wq);return NULL;}wq->name = name;lockdep_init_map(&wq->lockdep_map, lock_name, key, 0);wq->singlethread = singlethread;wq->freezeable = freezeable;wq->rt = rt;INIT_LIST_HEAD(&wq->list);if (singlethread) {//??cwq = init_cpu_workqueue(wq, singlethread_cpu);//把wq和cpu关联上err = create_workqueue_thread(cwq, singlethread_cpu);start_workqueue_thread(cwq, -1);} else {cpu_maps_update_begin();/* * We must place this wq on list even if the code below fails. * cpu_down(cpu) can remove cpu from cpu_populated_map before * destroy_workqueue() takes the lock, in that case we leak * cwq[cpu]->thread. */spin_lock(&workqueue_lock);list_add(&wq->list, &workqueues);//将list挂到一个全局的工作队列中，之后会通过container_of()访问spin_unlock(&workqueue_lock);/* * We must initialize cwqs for each possible cpu even if we * are going to call destroy_workqueue() finally. Otherwise * cpu_up() can hit the uninitialized cwq once we drop the * lock. */for_each_possible_cpu(cpu) {cwq = init_cpu_workqueue(wq, cpu);if (err || !cpu_online(cpu))continue;err = create_workqueue_thread(cwq, cpu);start_workqueue_thread(cwq, cpu);}cpu_maps_update_done();}if (err) {destroy_workqueue(wq);wq = NULL;}return wq;}