Implementing work-deferring mechanisms 延期任务
Softirqs: Executed in an atomic context # kernel/softirq.c ; <linux/interrupt.h>.
Tasklets: Executed in an atomic context
Workqueues: Executed in a process context
struct softirq_action { void (*action)(struct softirq_action *); };
void softirq_handler(struct softirq_action *h)
void open_softirq(int nr, void (*action)(struct softirq_action *))
nr represents the softirq index, which is also considered as the softirq priority (where 0 is the highest). action is a pointer to the softirq handler. Possible indexes are enumerated in the following code snippet:
enum {
HI_SOFTIRQ=0, /* High-priority tasklets */
TIMER_SOFTIRQ, /* Timers */
NET_TX_SOFTIRQ, /* Send network packets */
NET_RX_SOFTIRQ, /* Receive network packets */
BLOCK_SOFTIRQ, /* Block devices */
BLOCK_IOPOLL_SOFTIRQ, /* Block devices with I/O polling * blocked on other CPUs */
TASKLET_SOFTIRQ,/* Normal Priority tasklets */ SCHED_SOFTIRQ, /* Scheduler */
HRTIMER_SOFTIRQ,/* High-resolution timers */
RCU_SOFTIRQ, /* RCU locking */
NR_SOFTIRQS /* This only represent the number * of softirqs type, 10 actually */
}; #nr数值越小，优先级越大
const char * const softirq_to_name[NR_SOFTIRQS] = { "HI", "TIMER", "NET_TX", "NET_RX", "BLOCK", "BLOCK_IOPOLL", "TASKLET", "SCHED", "HRTIMER", "RCU" };
cat /proc/softirqs
void __raise_softirq_irqoff(unsigned int nr)
void raise_softirq_irqoff(unsigned int nr)
void raise_softirq(unsigned int nr)
Tasklets
void tasklet_setup(struct tasklet_struct *t, void (*callback)(struct tasklet_struct *)); deprecated
Workqueues
Worker threads, which are dedicated threads that execute and pull the functions off the queue, one by one, one after the other.
Worker pools: This is a collection of worker threads (a thread pool) that are used to better manage the worker threads.
linux/workqueue.h
DECLARE_WORK(name, function) #静态初始化一个work
DECLARE_DELAYED_WORK(name, function) #初始化一个延迟work
INIT_WORK(work, func ); #动态
INIT_DELAYED_WORK( work, func);
struct work_struct { atomic_long_t data; struct list_head entry; work_func_t func; };
struct delayed_work { struct work_struct work; struct timer_list timer; struct workqueue_struct *wq; int cpu; };
typedef void (*work_func_t)(struct work_struct *work);
struct delayed_work *to_delayed_work( struct work_struct *work)
struct workqueue_struct *create_workqueue(const char *name) #为每一个cpu创建一个专门的线程
struct workqueue_struct *create_singlethread_workqueue( const char *name)
bool queue_work(struct workqueue_struct *wq, struct work_struct *work) #排班work
bool queue_delayed_work(struct workqueue_struct *wq, struct delayed_work *dwork, unsigned long delay) #排延迟工作
取消work
bool cancel_work_sync(struct work_struct *work)
bool cancel_delayed_work(struct delayed_work *dwork)
bool cancel_delayed_work_sync(struct delayed_work *dwork)
void flush_workqueue(struct worksqueue_struct * queue);
void destroy_workqueue(structure workqueque_struct *queue); #摧毁工作队列
Kernel-global workqueue – the shared queue #在内核初始化时已经创建
int schedule_work(struct work_struct *work);
int schedule_delayed_work(struct delayed_work *dwork, unsigned long delay);
int schedule_work_on(int cpu, struct work_struct *work); #指定cpu排班任务
int schedule_delayed_work_on(int cpu, struct delayed_work *dwork, unsigned long delay);
void flush_scheduled_work(void);
Concurrency Managed Workqueue (cmwq),
struct workqueue_struct *alloc_workqueue(const char *fmt, unsigned int flags, int max_active, ...);
#define alloc_ordered_workqueue(fmt, flags, args...) [...] #processes each work item one by one in queued order (that is, first-in, first-out (FIFO) order).
void destroy_workqueue(struct workqueue_struct *wq)
flags:
WQ_UNBOUND 不绑定cpu 由系统自己分配
WQ_MEM_RECLAIM 可以内存救援
WQ_FREEZABLE 省电，随系统休眠而休眠
WQ_HIGHPRI 高优先级，保证立即执行
WQ_CPU_INTENSIVE 表明cpu集约型任务 会被其他任务delay
queue_work_on() 可以指定cpu
Note that schedule_work() is a wrapper that calls queue_work() on the system workqueue (system_wq), while schedule_work_on() is a wrapper around queue_work_on(). Also, keep in mind the following: system_wq = alloc_workqueue("events", 0, 0);. You can have a look at the workqueue_init_early() function in kernel/ workqueue.c in kernel sources to see how other system-wide workqueues are created.