Tasking

Work Queue

Allow kernel code to request that a function be called at some future time.

Basic usage is shown below：

1. Establish work queue：

   1. struct workqueue_struct is needed which is defined in <linux/workqueue.h>.

   2. There are two methods which can create the work queue:

      1. struct workqueue_struct *create_workqueue(const char *name);
         This function would return a workqueue that has a dedicated thread for each processor on the system.

      2. struct workqueue_struct *create_singlethread_workqueue(const char *name);
         This function would return a workqueue that has a single worker thread.

   3. After linux 2.6.63, there's a new mechanism called "Concurrency-managed workqueues", and there're two new function for creating the work queue:

      1. alloc_workqueue

      2. alloc_ordered_workqueue

         /**
          * alloc_ordered_workqueue - allocate an ordered workqueue
          * @name: name of the workqueue
          * @flags: WQ_* flags (only WQ_FREEZABLE and WQ_MEM_RECLAIM are meaningful)
          *
          * Allocate an ordered workqueue.  An ordered workqueue executes at
          * most one work item at any given time in the queued order.  They are
          * implemented as unbound workqueues with @max_active of one.
          *
          * RETURNS:
          * Pointer to the allocated workqueue on success, %NULL on failure.
          */
         

2. Submit a task to a workqueue

   1. At compile time

      DECLARE_WORK(name, void (*function)(void *), void *data);
      

   2. At runtime

      1. Prepre the work_struct

         INIT_WORK(struct work_struct *work, void (*function)(void *), void *data);
         PREPARE_WORK(struct work_struct *work, void (*function)(void *), void *data);
         

      2. Submitting work to a workqueue

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

reference: http://www.makelinux.net/ldd3/chp-7-sect-6