tasklet and workqueue(from linux kernel development )

difference between those two mechanism :

tasklet is delayed for short time ,and it cannot sleep !

workqueue can be delayed for long time ,and it can sleep in the interrupt time !

workqueue is treated as kernel thread !

tasklet is made on the top of softirq!

they all used in interrupt handler (bottom half )!

what is the softirq ?

it is a mechanism looksmart like software interrupt !

detail about workqueue:it deferred work into kernel thread! so code of this bottom half can run in the process context ! And workqueue has all the benefit of process !it is scheduled and can be sleep !

use workqueue is going to create a new kernel thread !

workqueue is usually an interface to create a kernel thread to handle workqueue elsewhere!

kernel thread is called worker thread !

the workqueue subsystem implement and provide a default worker thread for deferred work queue!

default worker thread (kernel thread )is named events/n,n is the processor number !

that is how much processor ,then how many work thread!we can create our own kernel thread if necessary !

default worker thread is preferred !but also our own worker thread get some benefit !

the worker thread is represented by the structure workerqueue _struct (like task_struct of process )

struct workqueue_struct {

struct cpu_workqueue_struct cpu_wq[NR_CPUS];/////////////////////////////////////////////////

struct list_head list;

const char *name;

int singlethread;

int freezeable;

int rt;

};

struct cpu_workqueue _struct is per -processor ! workqueue of each processor have one such structure !

struct cpu_workqueue_struct {

spinlock_t lock; /* lock protecting this structure */

struct list_head worklist; /* list of work */

wait_queue_head_t more_work;

struct work_struct *current_struct;

struct workqueue_struct *wq; /* associated workqueue_struct */

task_t *thread; /* associated thread *//////////////////////////////////////////////////////////////

};

each processor have one worker thread !

struct work_struct {

atomic_long_t data;

struct list_head entry;

work_func_t func;

};

function associated with worker thread

those structure is strung into a link list ! one node is each structure of worker thread of each processor