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tasklet、wait_queue、completion、work_queue用法总结
对于内核中常用的中断处理机制做一些总结,方便在合适的时候采用合适的机制。
tasklet 和 work_queue 是延期执行工作的机制,实现基于软中断;completion的实现基于wait_queue。
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tasklet
小进程,主要用于执行一些小任务,对这些任务使用全功能进程比较浪费。也称为中断下半部,在处理软中断时执行。
definition:
struct tasklet_struct{ struct tasklet_struct *next; unsigned long state; atomic_t count; void (*func)(unsigned long); unsigned long data;};
相关定义:
#define DECLARE_TASKLET(name, func, data) struct tasklet_struct name = { NULL, 0, ATOMIC_INIT(0), func, data }#define DECLARE_TASKLET_DISABLED(name, func, data) struct tasklet_struct name = { NULL, 0, ATOMIC_INIT(1), func, data }enum{ TASKLET_STATE_SCHED, /* Tasklet is scheduled for execution */ TASKLET_STATE_RUN /* Tasklet is running (SMP only) */};
初始化及销毁tasklet的方法:
void tasklet_init(struct tasklet_struct *t, void (*func)(unsigned long), unsigned long data){ t->next = NULL; t->state = 0; atomic_set(&t->count, 0); t->func = func; t->data = http://www.mamicode.com/data;>
调度tasklet的方法:
static inline void tasklet_schedule(struct tasklet_struct *t){ if (!test_and_set_bit(TASKLET_STATE_SCHED, &t->state)) __tasklet_schedule(t);}void __tasklet_schedule(struct tasklet_struct *t){ unsigned long flags; local_irq_save(flags); t->next = NULL; *__this_cpu_read(tasklet_vec.tail) = t; __this_cpu_write(tasklet_vec.tail, &(t->next)); raise_softirq_irqoff(TASKLET_SOFTIRQ); local_irq_restore(flags);}
使用方法:
tasklet_init->tasklet_schedule——————————————————————————————————————————————————————————————————————————————————————————————————————————————
wait_queue
用于使进程等待某一事件的发生,无须频繁轮讯,进程在等待期间睡眠,在事件发生时由内核自动唤醒。用法1(add_wait_queue 和 wake_up组合):
当nand控制器被一个进程使用时,其余进程被放入等待队列;待第一个进程使用结束后,调用wake_up唤醒等待队列,下一个进程获得nand控制器的使用权。
#define DECLARE_WAITQUEUE(name, tsk) wait_queue_t name = __WAITQUEUE_INITIALIZER(name, tsk)#define __WAITQUEUE_INITIALIZER(name, tsk) { .private = tsk, .func = default_wake_function, .task_list = { NULL, NULL } } void add_wait_queue(wait_queue_head_t *q, wait_queue_t *wait){ unsigned long flags; wait->flags &= ~WQ_FLAG_EXCLUSIVE; spin_lock_irqsave(&q->lock, flags); __add_wait_queue(q, wait); spin_unlock_irqrestore(&q->lock, flags);}<nand_base.c>static int nand_test_get_device(struct mtd_info *mtd, int new_state){ struct nand_chip *chip = mtd->priv; spinlock_t *lock = &chip->controller->lock; wait_queue_head_t *wq = &chip->controller->wq; DECLARE_WAITQUEUE(wait, current);retry: spin_lock(lock); /* Hardware controller shared among independent devices */ if (!chip->controller->active) chip->controller->active = chip; if (chip->controller->active == chip && chip->state == FL_READY) { chip->state = new_state; spin_unlock(lock); return 0; } if (new_state == FL_PM_SUSPENDED) { if (chip->controller->active->state == FL_PM_SUSPENDED) { chip->state = FL_PM_SUSPENDED; spin_unlock(lock); return 0; } } set_current_state(TASK_UNINTERRUPTIBLE); add_wait_queue(wq, &wait); spin_unlock(lock); schedule(); remove_wait_queue(wq, &wait); goto retry;}static void nand_test_release_device(struct mtd_info *mtd){ struct nand_chip *chip = mtd->priv; /* Release the controller and the chip */ spin_lock(&chip->controller->lock); chip->controller->active = NULL; chip->state = FL_READY; wake_up(&chip->controller->wq); spin_unlock(&chip->controller->lock);}
方法2(prepare_to_wait 和 wake_up组合),可作为实现阻塞的方式:
#define DEFINE_WAIT_FUNC(name, function) wait_queue_t name = { .private = current, .func = function, .task_list = LIST_HEAD_INIT((name).task_list), }#define DEFINE_WAIT(name) DEFINE_WAIT_FUNC(name, autoremove_wake_function)
autoremove_wake_function会调用default_wake_function,然后将所属等待队列成员从等待队列中删除。
voidprepare_to_wait(wait_queue_head_t *q, wait_queue_t *wait, int state){ unsigned long flags; wait->flags &= ~WQ_FLAG_EXCLUSIVE; spin_lock_irqsave(&q->lock, flags); if (list_empty(&wait->task_list)) __add_wait_queue(q, wait); set_current_state(state); spin_unlock_irqrestore(&q->lock, flags);}static long do_CustomEvent_wait(long eventNum) { struct CustomEvent *tmp = NULL; struct CustomEvent *prev = NULL; pr_info("Enten into %s, the eventNum is %d\n", __func__, eventNum); if((tmp = FindEventNum(eventNum, &prev)) != NULL) { DEFINE_WAIT(wait); prepare_to_wait(tmp->p, &wait, TASK_INTERRUPTIBLE); schedule(); finish_wait(tmp->p, &wait); return eventNum; } return -1;}static long do_CustomEvent_signal(long eventNum){ struct CustomEvent *tmp = NULL; struct CustomEvent *prev = NULL; pr_info("Enten into %s, the eventNum is %d\n", __func__, eventNum); if(!(tmp = FindEventNum(eventNum, &prev))) return 0; wake_up(tmp->p); return 1;}
第三种方法(wait_event 和 wake_up组合):
该方法首先将进程的状态设为 TASK_UNINTERRUPTIBLE, 之后判断条件是否满足;条件不满足时,通过schedule()将该进程从runqueue队列中移除,该进程进入睡眠状态;只有当某进程调用wake_up才能再次唤醒该进程;进程被唤醒后,再次将该进程的状态置为TASK_UNINTERRUPTIBLE,然后判断条件是否满足。条件满足时结束循环,由finish_wait将进程的状态设置为TASK_RUNNING,并从等待队列的链表中移除相应项。
#define __wait_event(wq, condition) do { DEFINE_WAIT(__wait); for (;;) { prepare_to_wait(&wq, &__wait, TASK_UNINTERRUPTIBLE); if (condition) break; schedule(); } finish_wait(&wq, &__wait); } while (0)#define wait_event(wq, condition) do { if (condition) break; __wait_event(wq, condition); } while (0)
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completion:
基于等待队列,内核利用该机制等待某一操作结束。由于和wait_queue用法类似,不再详细描述。
completion的操作接口:
init_completion()封装了init_waitqueue_head()接口;
wait_for_completion()封装了wait_for_common()接口;
complete()封装了__wake_up_common()接口。——————————————————————————————————————————————————————————————————————————————————————————————————————————————
work_queue:由于在中断中不能进行阻塞型操作,而有时候需要在中断时读取某些内存单元或寄存器的值,此时可以考虑利用工作队列来实现。
工作队列的定义:
工作队列是将操作延期的一种手段。因为他们是通过守护进程在用户上下文执行,函数可以睡眠任意长的时间,这与内核无关。替换了之前的kevented机制。
工作队列的使用:使用工作队列,主要有以下三个步骤:
1 实现工作任务处理函数
2 创建并初始化工作任务
3 将工作任务添加到某工作队列中,等待系统调度
<kernel/workqueue.c>int schedule_work(struct work_struct *work)int schedule_delayed_work(struct work_struct *dwork, unsigned long delay)
1 定义工作任务处理函数:
static void func(struct work_struct *work){......}
2 创建并初始化工作任务
可采用两种方式创建并初始化工作任务:
1) 先创建工作任务,后绑定处理函数:
struct work_struct xxx_wq;//创建工作任务
在模块初始化的时候:
INIT_WORK(&xxx_wq,func);//初始化工作任务,工作任务需要执行的是函数func
2) 创建工作任务的同时初始化:
DECLARE_WORK(xxx_wq, func);
3 在中断处理函数中将工作任务添加到工作队列,等待系统调度static inline bool queue_work(struct workqueue_struct *wq, struct work_struct *work){ return queue_work_on(WORK_CPU_UNBOUND, wq, work);}
用于将某工作任务添加到某工作队列内核创建了一个标准的工作队列events,内核的各个部分若无必要创建独立的工作队列,可直接使用该工作队列。
static inline bool schedule_work(struct work_struct *work)//将工作任务xxx_wq添加到标准工作队列events中,中断处理完成之后可以立即执行func{ return queue_work(system_wq, work);}
tasklet、wait_queue、completion、work_queue用法总结