前面介绍了工作队列相关数据结构定义，那么对于工作队列上的任务什么时候执行呢？以及相关
数据结构是什么呢？
工作队列中，执行任务的叫worker，这些worker构成worker_pool。所以有下面定义：
/*
* The poor guys doing the actual heavy lifting. All on-duty workers are
* either serving the manager role, on idle list or on busy hash. For
* details on the locking annotation (L, I, X...), refer to workqueue.c.
*
* Only to be used in workqueue and async.
*/
struct worker {
/* on idle list while idle, on busy hash table while busy */
union {
struct list_head entry; /* L: while idle */
struct hlist_node hentry; /* L: while busy */
};
struct work_struct *current_work; /* L: work being processed */
work_func_t current_func; /* L: current_work's fn */
struct pool_workqueue *current_pwq; /* L: current_work's pwq */
bool desc_valid; /* ->desc is valid */
struct list_head scheduled; /* L: scheduled works */
/* 64 bytes boundary on 64bit, 32 on 32bit */
struct task_struct *task; /* I: worker task */
struct worker_pool *pool; /* I: the associated pool */
/* L: for rescuers */
struct list_head node; /* A: anchored at pool->workers */
/* A: runs through worker->node */
unsigned long last_active; /* L: last active timestamp */
unsigned int flags; /* X: flags */
int id; /* I: worker id */
/*
* Opaque string set with work_set_desc(). Printed out with task
* dump for debugging - WARN, BUG, panic or sysrq.
*/
char desc[WORKER_DESC_LEN];
/* used only by rescuers to point to the target workqueue */
struct workqueue_struct *rescue_wq; /* I: the workqueue to rescue */
};
/*
* Structure fields follow one of the following exclusion rules.
*
* I: Modifiable by initialization/destruction paths and read-only for
* everyone else.
*
* P: Preemption protected. Disabling preemption is enough and should
* only be modified and accessed from the local cpu.
*
* L: pool->lock protected. Access with pool->lock held.
*
* X: During normal operation, modification requires pool->lock and should
* be done only from local cpu. Either disabling preemption on local
* cpu or grabbing pool->lock is enough for read access. If
* POOL_DISASSOCIATED is set, it's identical to L.
*
* A: pool->attach_mutex protected.
*
* PL: wq_pool_mutex protected.
*
* PR: wq_pool_mutex protected for writes. Sched-RCU protected for reads.
*
* PW: wq_pool_mutex and wq->mutex protected for writes. Either for reads.
*
* PWR: wq_pool_mutex and wq->mutex protected for writes. Either or
* sched-RCU for reads.
*
* WQ: wq->mutex protected.
*
* WR: wq->mutex protected for writes. Sched-RCU protected for reads.
*
* MD: wq_mayday_lock protected.
*/
/* struct worker is defined in workqueue_internal.h */
struct worker_pool {
spinlock_t lock; /* the pool lock */
int cpu; /* I: the associated cpu */
int node; /* I: the associated node ID */
int id; /* I: pool ID */
unsigned int flags; /* X: flags */
unsigned long watchdog_ts; /* L: watchdog timestamp */
struct list_head worklist; /* L: list of pending works */
int nr_workers; /* L: total number of workers */
/* nr_idle includes the ones off idle_list for rebinding */
int nr_idle; /* L: currently idle ones */
struct list_head idle_list; /* X: list of idle workers */
struct timer_list idle_timer; /* L: worker idle timeout */
struct timer_list mayday_timer; /* L: SOS timer for workers */
/* a workers is either on busy_hash or idle_list, or the manager */
DECLARE_HASHTABLE(busy_hash, BUSY_WORKER_HASH_ORDER);
/* L: hash of busy workers */
/* see manage_workers() for details on the two manager mutexes */
struct mutex manager_arb; /* manager arbitration */
struct worker *manager; /* L: purely informational */
struct mutex attach_mutex; /* attach/detach exclusion */
struct list_head workers; /* A: attached workers */
struct completion *detach_completion; /* all workers detached */
struct ida worker_ida; /* worker IDs for task name */
struct workqueue_attrs *attrs; /* I: worker attributes */
struct hlist_node hash_node; /* PL: unbound_pool_hash node */
int refcnt; /* PL: refcnt for unbound pools */
/*
* The current concurrency level. As it's likely to be accessed
* from other CPUs during try_to_wake_up(), put it in a separate
* cacheline.
*/
atomic_t nr_running ____cacheline_aligned_in_smp;
/*
* Destruction of pool is sched-RCU protected to allow dereferences
* from get_work_pool().
*/
struct rcu_head rcu;
} ____cacheline_aligned_in_smp;
内核对worker创建由函数 struct worker *create_worker(struct worker_pool *pool)
处理，worker->task这个绑定了一个内核线程。
/**
* create_worker - create a new workqueue worker
* @pool: pool the new worker will belong to
*
* Create a new worker which is bound to @pool. The returned worker
* can be started by calling start_worker() or destroyed using
* destroy_worker().
*
* CONTEXT:
* Might sleep. Does GFP_KERNEL allocations.
*
* RETURNS:
* Pointer to the newly created worker.
*/
static struct worker *create_worker(struct worker_pool *pool)
{
struct worker *worker = NULL;
int id = -1;
char id_buf[16];
lockdep_assert_held(&pool->manager_mutex);
/*
* ID is needed to determine kthread name. Allocate ID first
* without installing the pointer.
*/
idr_preload(GFP_KERNEL);
spin_lock_irq(&pool->lock);
id = idr_alloc(&pool->worker_idr, NULL, 0, 0, GFP_NOWAIT);
spin_unlock_irq(&pool->lock);
idr_preload_end();
if (id < 0)
goto fail;
worker = alloc_worker();
if (!worker)
goto fail;
worker->pool = pool;
worker->id = id;
if (pool->cpu >= 0)
snprintf(id_buf, sizeof(id_buf), "%d:%d%s", pool->cpu, id,
pool->attrs->nice < 0 ? "H" : "");
else
snprintf(id_buf, sizeof(id_buf), "u%d:%d", pool->id, id);
worker->task = kthread_create_on_node(worker_thread, worker, pool->node,
"kworker/%s", id_buf);
if (IS_ERR(worker->task))
goto fail;
/*
* set_cpus_allowed_ptr() will fail if the cpumask doesn't have any
* online CPUs. It'll be re-applied when any of the CPUs come up.
*/
set_user_nice(worker->task, pool->attrs->nice);
set_cpus_allowed_ptr(worker->task, pool->attrs->cpumask);
/* prevent userland from meddling with cpumask of workqueue workers */
worker->task->flags |= PF_NO_SETAFFINITY;
/*
* The caller is responsible for ensuring %POOL_DISASSOCIATED
* remains stable across this function. See the comments above the
* flag definition for details.
*/
if (pool->flags & POOL_DISASSOCIATED)
worker->flags |= WORKER_UNBOUND;
/* successful, commit the pointer to idr */
spin_lock_irq(&pool->lock);
idr_replace(&pool->worker_idr, worker, worker->id);
spin_unlock_irq(&pool->lock);
return worker;
fail:
if (id >= 0) {
spin_lock_irq(&pool->lock);
idr_remove(&pool->worker_idr, id);
spin_unlock_irq(&pool->lock);
}
kfree(worker);
return NULL;
}
任务唤醒函数：
static void wake_up_worker(struct worker_pool *pool)
{
struct worker *worker = first_worker(pool);
if (likely(worker))
wake_up_process(worker->task);
}
