Operating queue in Linux kernel

Article Title: how to operate a work queue in the Linux operating system kernel. Linux is a technology channel of the IT lab in China. Includes basic categories such as desktop applications, Linux system management, kernel research, embedded systems, and open source.

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1. Preface

The method defined in the Linux kernel of workqueue is used to handle callback methods that are not very urgent.

The Linux kernel version of the following code is 2.6.19.2. the source code file is mainly kernel/workqueue. c.

2. Data structure

/* Include/linux/workqueue. h */

// Work node structure

Struct work_struct {

// Wait time

Unsigned long pending;

// Linked list node

Struct list_head entry;

// Workqueue callback function

Void (* func) (void *);

// Callback function func data

Void * data;

// Point to CPU-related data, generally to the struct cpu_workqueue_struct structure

Void * wq_data;

// Timer

Struct timer_list timer;

};

Struct execute_work {

Struct work_struct work;

};

/* Kernel/workqueue. c */

/*

* The per-CPU workqueue (if single thread, we always use the first

* Possible cpu ).

*

* The sequence counters are for flush_scheduled_work (). It wants to wait

* Until all currently-scheduled works are completed, but it doesn' t

* Want to be livelocked by new, incoming ones. So it waits

* Remove_sequence is> = the insert_sequence which pertained when

* Flush_scheduled_work () was called.

*/

// This structure is for each CPU

Struct cpu_workqueue_struct {

// Structure lock

Spinlock_t lock;

// The number of the next node to be executed

Long remove_sequence;/* Least-recently added (next to run )*/

// The serial number of the next node to be inserted

Long insert_sequence;/* Next to add */

// Linked list node of the working organization

Struct list_head worklist;

// Waiting queue for processing

Wait_queue_head_t more_work;

// Wait queue after processing

Wait_queue_head_t work_done;

// Work queue node

Struct workqueue_struct * wq;

// Process pointer

Struct task_struct * thread;

Int run_depth;/* Detect run_workqueue () recursion depth */

}____ Cacheline_aligned;

/*

* The externally visible workqueue specified action is an array

* Per-CPU workqueues:

*/

// Work queue structure

Struct workqueue_struct {

Struct cpu_workqueue_struct * cpu_wq;

Const char * name;

Struct list_head list;/* Empty if single thread */

};

A work queue linked list is defined in kernel/workqueue. c. All Work queues can be attached to this linked list:

Static LIST_HEAD (workqueues );

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