# First, the upper half and the lower half

Origin:

1. The problem caused by the long execution time of the interrupt handler

2. The interrupt handler of some devices must handle some time-consuming operations

# Second, the tasklet of the lower half mechanism ---- based on soft interrupt

##6.1 Structures

struct tasklet_struct

{

​ struct tasklet_struct *next;

​ unsigned long state;

​ atomic_t count;

​ void (*func)(unsigned long);

​ unsigned long data;

};

## 6.2 Define tasklet interrupt bottom half handler

void tasklet_func(unsigned long data);

## 6.3 Initialize tasklet

```c

DECLARE_TASKLET(name, func, data);

/*

Define variables and initialize

Parameters: name: The name of the tasklet in the bottom half of the interrupt

Func: The name of the bottom half of the interrupt handler

data: parameter passed to the interrupt bottom half handler

*/

```

```c

void tasklet_init(struct tasklet_struct *t,void (*func)(unsigned long), unsigned long data)

```

## 6.4 Scheduling tasklets

```c

void tasklet_schedule(struct tasklet_struct *t)

//Parameter: t: structure of tasklet

```

# 3. Tasklet version driven by keys

# Fourth, the workqueue of the lower half mechanism ----- based on kernel threads

##8.1 Work queue structure:

typedef void (*work_func_t)(struct work_struct *work)

struct work_struct {

​ atomic_long_t data;

​   struct list_head entry;

​  work_func_t func;

\#ifdef CONFIG_LOCKDEP

​     struct lockdep_map lockdep_map;

\#endif

};

##8.2 Define the bottom half of the work queue processing function

void work_queue_func(struct work_struct *work);

##8.3 Initializing the work queue

struct work_struct work_queue;

Initialization: bind the work queue and the bottom half processing function of the work queue

INIT_WORK(struct work_struct * pwork, _func) ;

parameters: pwork: work queue

​ func: the bottom half of the work queue processing function

## 8.4 Scheduling functions for work queues

bool schedule_work(struct work_struct *work);

# Five, button-driven workqueue version

# Six, the lower half mechanism comparison

Task mechanism

​ Workqueue ----- Kernel thread can sleep unlimited running time

Exception mechanism ------- Cannot sleep The execution time of the second half should not be too long ( < 1s)

​ Soft interrupt ---- interface is inconvenient

​ tasklet ----- When there is no specific delay time requirement

​ Timer -----When there is a specific delay time request