一、用法
struct cpu_workqueue_struct { spinlock_t lock; long remove_sequence; /* Least-recently added (next to run) */
long insert_sequence; /* Next to add */ struct list_head worklist;
wait_queue_head_t more_work;
wait_queue_head_t work_done; struct workqueue_struct *wq;
struct task_struct *thread; int run_depth; /* Detect run_workqueue() recursion depth */
} ____cacheline_aligned; /*
* The externally visible workqueue abstraction is an array of
* per-CPU workqueues:
*/
struct workqueue_struct {
struct cpu_workqueue_struct *cpu_wq;
const char *name;
struct list_head list; /* Empty if single thread */
}; 工作隊列的使用很簡單。
1.首先是建立一個工作隊列：
struct workqueue_struct *keventd_wq;
keventd_wq = create_workqueue("events");
2.然後就是在這個隊列中insert你所要做的“工作”：
DECLARE_WORK(work, func, data)
queue_work(keventd_wq, work); struct work_struct {
unsigned long pending;
struct list_head entry;
void (*func)(void *);
void *data;
void *wq_data;
struct timer_list timer;
}; 初始化有兩種方法。
一種為靜態方法：
#define __WORK_INITIALIZER(n, f, d) { \
.entry = { &(n).entry, &(n).entry }, \
.func = (f), \
.data = (d), \
.timer = TIMER_INITIALIZER(NULL, 0, 0), \
} #define DECLARE_WORK(n, f, d) \
struct work_struct n = __WORK_INITIALIZER(n, f, d) 另一種為動態方法：
/*
* initialize all of a work-struct:
*/
#define INIT_WORK(_work, _func, _data) \
do { \
INIT_LIST_HEAD(&(_work)->entry); \
(_work)->pending = 0; \
PREPARE_WORK((_work), (_func), (_data)); \
init_timer(&(_work)->timer); \
} while (0) 二、執行過程
create_workqueue() -> __create_workqueue() struct workqueue_struct *__create_workqueue(const char *name,
int singlethread)
{
int cpu, destroy = 0;
struct workqueue_struct *wq;
struct task_struct *p; wq = kzalloc(sizeof(*wq), GFP_KERNEL);
//為每個CPU建立一個結構
wq->cpu_wq = alloc_percpu(struct cpu_workqueue_struct);
...
wq->name = name;
mutex_lock(&workqueue_mutex);
if (singlethread) {
...
} else {
list_add(&wq->list, &workqueues);
for_each_online_cpu(cpu) {
//為每個CPU建立一個線程
p = create_workqueue_thread(wq, cpu);
if (p) {
kthread_bind(p, cpu);
//喚醒這個線程執行工作
wake_up_process(p);
} else
destroy = 1;
}
}
mutex_unlock(&workqueue_mutex);
...
return wq;
} create_workqueue() -> __create_workqueue() -> create_workqueue_thread() static struct task_struct *create_workqueue_thread(struct workqueue_struct *wq,
int cpu)
{
struct cpu_workqueue_struct *cwq = per_cpu_ptr(wq->cpu_wq, cpu);
struct task_struct *p; spin_lock_init(&cwq->lock);
cwq->wq = wq;
cwq->thread = NULL;
cwq->insert_sequence = 0;
cwq->remove_sequence = 0;
INIT_LIST_HEAD(&cwq->worklist);
init_waitqueue_head(&cwq->more_work);
init_waitqueue_head(&cwq->work_done); if (is_single_threaded(wq))
p = kthread_create(worker_thread, cwq, "%s", wq->name);
else
//建立一個線程，這個線程以cwq為資料執行worker_thread這個函數
p = kthread_create(worker_thread, cwq, "%s/%d", wq->name, cpu);
if (IS_ERR(p))
return NULL;
cwq->thread = p; //
return p;
} create_workqueue() -> __create_workqueue() -> create_workqueue_thread() -> worker_thread() //本函數在一個死迴圈等待工作的到來，這一般在睡眠狀態中，等待被喚醒執行工作
//當有工作到來時queue_work()會將這個線程喚醒
static int worker_thread(void *__cwq)
{
struct cpu_workqueue_struct *cwq = __cwq;
DECLARE_WAITQUEUE(wait, current);
... current->flags |= PF_NOFREEZE; //設定優先權
set_user_nice(current, -5);
...
set_current_state(TASK_INTERRUPTIBLE);
while (!kthread_should_stop()) {
//將本線程加入睡眠隊列，用於睡眠後可以被喚醒
add_wait_queue(&cwq->more_work, &wait); //如果沒用被執行的“工作”，則將自己切換出去，進入睡眠狀態
if (list_empty(&cwq->worklist))
schedule();
else //否則或是被喚醒
__set_current_state(TASK_RUNNING);
remove_wait_queue(&cwq->more_work, &wait); //工作隊列非空，執行工作
if (!list_empty(&cwq->worklist))
run_workqueue(cwq);
set_current_state(TASK_INTERRUPTIBLE);
}
__set_current_state(TASK_RUNNING);
return 0;
} create_workqueue() -> __create_workqueue() -> create_workqueue_thread()
-> worker_thread() -> run_workqueue()
//該函數執行真正的工作
static void run_workqueue(struct cpu_workqueue_struct *cwq)
{
unsigned long flags; spin_lock_irqsave(&cwq->lock, flags);
...
//順次執行隊列中的所有工作
while (!list_empty(&cwq->worklist)) {
struct work_struct *work = list_entry(cwq->worklist.next,
struct work_struct, entry);
void (*f) (void *) = work->func;
void *data = work->data; //從隊列中刪除待執行的任務
list_del_init(cwq->worklist.next);
spin_unlock_irqrestore(&cwq->lock, flags); BUG_ON(work->wq_data != cwq);
clear_bit(0, &work->pending); //執行“工作”
f(data); spin_lock_irqsave(&cwq->lock, flags);
cwq->remove_sequence++;
wake_up(&cwq->work_done); //
}
cwq->run_depth--;
spin_unlock_irqrestore(&cwq->lock, flags);
} 三、背景工作執行緒建立的詳細過程
create_workqueue() -> __create_workqueue() -> create_workqueue_thread()
-> kthread_create() struct task_struct *kthread_create(int (*threadfn)(void *data),
void *data,
const char namefmt[],
...)
{
//初始化用於建立線程的輔助結構
struct kthread_create_info create;
DECLARE_WORK(work, keventd_create_kthread, &create);
create.threadfn = threadfn;
create.data = data;
init_completion(&create.started);
init_completion(&create.done); if (!helper_wq) //首先建立輔助工作隊列
work.func(work.data);
else {
//注意，“建立一個工作隊列”這個工作本身又是屬於helper_wq工作隊列
//的一項工作，所以，將這個工作加入的輔助工作隊列中等待執行。
queue_work(helper_wq, &work);
wait_for_completion(&create.done);
}
...
return create.result;
} create_workqueue() -> __create_workqueue() -> create_workqueue_thread()
-> kthread_create()-> keventd_create_kthread()
//最終會調用kernel_thread為每個工作隊列建立一個線程
//這樣，被建立的線程會以create為資料執行kthread(如下),而kthread中則執行create中的threadfn(data)，
//即為create_workqueue_thread中的worker_thread(cwq)，即為我們工作隊列要執行的函數了。 static void keventd_create_kthread(void *_create)
{
struct kthread_create_info *create = _create;
int pid; /* We want our own signal handler (we take no signals by default). */
pid = kernel_thread(kthread, create, CLONE_FS | CLONE_FILES | SIGCHLD);
if (pid < 0) {
create->result = ERR_PTR(pid);
} else {
wait_for_completion(&create->started);
read_lock(&tasklist_lock);
create->result = find_task_by_pid(pid);
read_unlock(&tasklist_lock);
}
complete(&create->done);
} static int kthread(void *_create)
{
struct kthread_create_info *create = _create;
int (*threadfn)(void *data);
void *data;
...
threadfn = create->threadfn;
data = create->data;
...
if (!kthread_should_stop())
ret = threadfn(data);
...
return 0;
} 四、插入“工作”
/* Preempt must be disabled. */
static void __queue_work(struct cpu_workqueue_struct *cwq,
struct work_struct *work)
{
unsigned long flags; spin_lock_irqsave(&cwq->lock, flags);
work->wq_data = cwq;
//將當前工作插入到工作隊列中待待執行
list_add_tail(&work->entry, &cwq->worklist);
cwq->insert_sequence++;
wake_up(&cwq->more_work); //喚醒相應線程
spin_unlock_irqrestore(&cwq->lock, flags);
} int fastcall queue_work(struct workqueue_struct *wq, struct work_struct *work)
{
int ret = 0, cpu = get_cpu(); //如裡當前工作未在隊列中才插入
if (!test_and_set_bit(0, &work->pending)) {
...
__queue_work(per_cpu_ptr(wq->cpu_wq, cpu), work);
ret = 1;
}
put_cpu();
return ret;
} |
