Linux 内核工作队列

工作队列也是内核一种延时执行任务机制，显然，内核需要定义一个队列，然后队列上面存放需要执行的任务，而任务执行则有内核线程来调用任务。

工作队列定义如下：

/* * The externally visible workqueue.  It relays the issued work items to * the appropriate worker_pool through its pool_workqueues. */struct workqueue_struct { struct list_head pwqs;  /* WR: all pwqs of this wq */ struct list_head list;  /* PR: list of all workqueues */
 struct mutex  mutex;  /* protects this wq */ int   work_color; /* WQ: current work color */ int   flush_color; /* WQ: current flush color */ atomic_t  nr_pwqs_to_flush; /* flush in progress */ struct wq_flusher *first_flusher; /* WQ: first flusher */ struct list_head flusher_queue; /* WQ: flush waiters */ struct list_head flusher_overflow; /* WQ: flush overflow list */
 struct list_head maydays; /* MD: pwqs requesting rescue */ struct worker  *rescuer; /* I: rescue worker */
 int   nr_drainers; /* WQ: drain in progress */ int   saved_max_active; /* WQ: saved pwq max_active */
 struct workqueue_attrs *unbound_attrs; /* PW: only for unbound wqs */ struct pool_workqueue *dfl_pwq; /* PW: only for unbound wqs */
#ifdef CONFIG_SYSFS struct wq_device *wq_dev; /* I: for sysfs interface */#endif#ifdef CONFIG_LOCKDEP struct lockdep_map lockdep_map;#endif char   name[WQ_NAME_LEN]; /* I: workqueue name */
 /*  * Destruction of workqueue_struct is sched-RCU protected to allow  * walking the workqueues list without grabbing wq_pool_mutex.  * This is used to dump all workqueues from sysrq.  */ struct rcu_head  rcu;
 /* hot fields used during command issue, aligned to cacheline */ unsigned int  flags ____cacheline_aligned; /* WQ: WQ_* flags */ struct pool_workqueue __percpu *cpu_pwqs; /* I: per-cpu pwqs */ struct pool_workqueue __rcu *numa_pwq_tbl[]; /* PWR: unbound pwqs indexed by node */};
队列上任务定义如下：
struct work_struct { atomic_long_t data; struct list_head entry; work_func_t func;#ifdef CONFIG_LOCKDEP struct lockdep_map lockdep_map;#endif};

或者一种带有延时性质的任务：

struct delayed_work { struct work_struct work; struct timer_list timer;
 /* target workqueue and CPU ->timer uses to queue ->work */ struct workqueue_struct *wq; int cpu;};
工作任务加入工作队列由函数__queue_work()处理，其对外提供接口有：
1. 指定CPU下队列
bool queue_work_on(int cpu, struct workqueue_struct *wq,     struct work_struct *work)

2. 延时加入

void delayed_work_timer_fn(unsigned long __data)

3.

void __queue_delayed_work(int cpu, struct workqueue_struct *wq,    struct delayed_work *dwork, unsigned long delay) 

bool queue_delayed_work_on(int cpu, struct workqueue_struct *wq,      struct delayed_work *dwork, unsigned long delay)

4.

bool flush_delayed_work(struct delayed_work *dwork)

内核中常用的队列：

extern struct workqueue_struct *system_wq;extern struct workqueue_struct *system_highpri_wq;extern struct workqueue_struct *system_long_wq;extern struct workqueue_struct *system_unbound_wq;extern struct workqueue_struct *system_freezable_wq;extern struct workqueue_struct *system_power_efficient_wq;extern struct workqueue_struct *system_freezable_power_efficient_wq;