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;