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workqueue: implement worker states

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Implement worker states.  After created, a worker is STARTED.  While a
worker isn't processing a work, it's IDLE and chained on
gcwq->idle_list.  While processing a work, a worker is BUSY and
chained on gcwq->busy_hash.  Also, gcwq now counts the number of all
workers and idle ones.

worker_thread() is restructured to reflect state transitions.
cwq->more_work is removed and waking up a worker makes it check for
events.  A worker is killed by setting DIE flag while it's IDLE and
waking it up.

This gives gcwq better visibility of what's going on and allows it to
find out whether a work is executing quickly which is necessary to
have multiple workers processing the same cwq.

Signed-off-by: Tejun Heo <tj@kernel.org>
This commit is contained in:
Tejun Heo 2010-06-29 10:07:12 +02:00
parent 8b03ae3cde
commit c8e55f3602
1 changed files with 176 additions and 44 deletions
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220
kernel/workqueue.c
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@ -35,6 +35,17 @@
#include <linux/lockdep.h>
#include <linux/idr.h>
enum {
/* worker flags */
WORKER_STARTED = 1 << 0, /* started */
WORKER_DIE = 1 << 1, /* die die die */
WORKER_IDLE = 1 << 2, /* is idle */
BUSY_WORKER_HASH_ORDER = 6, /* 64 pointers */
BUSY_WORKER_HASH_SIZE = 1 << BUSY_WORKER_HASH_ORDER,
BUSY_WORKER_HASH_MASK = BUSY_WORKER_HASH_SIZE - 1,
};
/*
* Structure fields follow one of the following exclusion rules.
*
@ -51,11 +62,18 @@ struct global_cwq;
struct cpu_workqueue_struct;
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 */
struct list_head scheduled; /* L: scheduled works */
struct task_struct *task; /* I: worker task */
struct global_cwq *gcwq; /* I: the associated gcwq */
struct cpu_workqueue_struct *cwq; /* I: the associated cwq */
unsigned int flags; /* L: flags */
int id; /* I: worker id */
};
@ -65,6 +83,15 @@ struct worker {
struct global_cwq {
spinlock_t lock; /* the gcwq lock */
unsigned int cpu; /* I: the associated cpu */
int nr_workers; /* L: total number of workers */
int nr_idle; /* L: currently idle ones */
/* workers are chained either in the idle_list or busy_hash */
struct list_head idle_list; /* L: list of idle workers */
struct hlist_head busy_hash[BUSY_WORKER_HASH_SIZE];
/* L: hash of busy workers */
struct ida worker_ida; /* L: for worker IDs */
} ____cacheline_aligned_in_smp;
@ -77,7 +104,6 @@ struct global_cwq {
struct cpu_workqueue_struct {
struct global_cwq *gcwq; /* I: the associated gcwq */
struct list_head worklist;
wait_queue_head_t more_work;
struct worker *worker;
struct workqueue_struct *wq; /* I: the owning workqueue */
int work_color; /* L: current color */
@ -306,6 +332,33 @@ static inline struct cpu_workqueue_struct *get_wq_data(struct work_struct *work)
WORK_STRUCT_WQ_DATA_MASK);
}
/**
* busy_worker_head - return the busy hash head for a work
* @gcwq: gcwq of interest
* @work: work to be hashed
*
* Return hash head of @gcwq for @work.
*
* CONTEXT:
* spin_lock_irq(gcwq->lock).
*
* RETURNS:
* Pointer to the hash head.
*/
static struct hlist_head *busy_worker_head(struct global_cwq *gcwq,
struct work_struct *work)
{
const int base_shift = ilog2(sizeof(struct work_struct));
unsigned long v = (unsigned long)work;
/* simple shift and fold hash, do we need something better? */
v >>= base_shift;
v += v >> BUSY_WORKER_HASH_ORDER;
v &= BUSY_WORKER_HASH_MASK;
return &gcwq->busy_hash[v];
}
/**
* insert_work - insert a work into cwq
* @cwq: cwq @work belongs to
@ -332,7 +385,7 @@ static void insert_work(struct cpu_workqueue_struct *cwq,
smp_wmb();
list_add_tail(&work->entry, head);
wake_up(&cwq->more_work);
wake_up_process(cwq->worker->task);
}
static void __queue_work(unsigned int cpu, struct workqueue_struct *wq,
@ -470,13 +523,59 @@ int queue_delayed_work_on(int cpu, struct workqueue_struct *wq,
}
EXPORT_SYMBOL_GPL(queue_delayed_work_on);
/**
* worker_enter_idle - enter idle state
* @worker: worker which is entering idle state
*
* @worker is entering idle state. Update stats and idle timer if
* necessary.
*
* LOCKING:
* spin_lock_irq(gcwq->lock).
*/
static void worker_enter_idle(struct worker *worker)
{
struct global_cwq *gcwq = worker->gcwq;
BUG_ON(worker->flags & WORKER_IDLE);
BUG_ON(!list_empty(&worker->entry) &&
(worker->hentry.next || worker->hentry.pprev));
worker->flags |= WORKER_IDLE;
gcwq->nr_idle++;
/* idle_list is LIFO */
list_add(&worker->entry, &gcwq->idle_list);
}
/**
* worker_leave_idle - leave idle state
* @worker: worker which is leaving idle state
*
* @worker is leaving idle state. Update stats.
*
* LOCKING:
* spin_lock_irq(gcwq->lock).
*/
static void worker_leave_idle(struct worker *worker)
{
struct global_cwq *gcwq = worker->gcwq;
BUG_ON(!(worker->flags & WORKER_IDLE));
worker->flags &= ~WORKER_IDLE;
gcwq->nr_idle--;
list_del_init(&worker->entry);
}
static struct worker *alloc_worker(void)
{
struct worker *worker;
worker = kzalloc(sizeof(*worker), GFP_KERNEL);
if (worker)
if (worker) {
INIT_LIST_HEAD(&worker->entry);
INIT_LIST_HEAD(&worker->scheduled);
}
return worker;
}
@ -541,13 +640,16 @@ static struct worker *create_worker(struct cpu_workqueue_struct *cwq, bool bind)
* start_worker - start a newly created worker
* @worker: worker to start
*
* Start @worker.
* Make the gcwq aware of @worker and start it.
*
* CONTEXT:
* spin_lock_irq(gcwq->lock).
*/
static void start_worker(struct worker *worker)
{
worker->flags |= WORKER_STARTED;
worker->gcwq->nr_workers++;
worker_enter_idle(worker);
wake_up_process(worker->task);
}
@ -555,7 +657,10 @@ static void start_worker(struct worker *worker)
* destroy_worker - destroy a workqueue worker
* @worker: worker to be destroyed
*
* Destroy @worker.
* Destroy @worker and adjust @gcwq stats accordingly.
*
* CONTEXT:
* spin_lock_irq(gcwq->lock) which is released and regrabbed.
*/
static void destroy_worker(struct worker *worker)
{
@ -566,12 +671,21 @@ static void destroy_worker(struct worker *worker)
BUG_ON(worker->current_work);
BUG_ON(!list_empty(&worker->scheduled));
if (worker->flags & WORKER_STARTED)
gcwq->nr_workers--;
if (worker->flags & WORKER_IDLE)
gcwq->nr_idle--;
list_del_init(&worker->entry);
worker->flags |= WORKER_DIE;
spin_unlock_irq(&gcwq->lock);
kthread_stop(worker->task);
kfree(worker);
spin_lock_irq(&gcwq->lock);
ida_remove(&gcwq->worker_ida, id);
spin_unlock_irq(&gcwq->lock);
}
/**
@ -686,6 +800,7 @@ static void process_one_work(struct worker *worker, struct work_struct *work)
{
struct cpu_workqueue_struct *cwq = worker->cwq;
struct global_cwq *gcwq = cwq->gcwq;
struct hlist_head *bwh = busy_worker_head(gcwq, work);
work_func_t f = work->func;
int work_color;
#ifdef CONFIG_LOCKDEP
@ -700,6 +815,7 @@ static void process_one_work(struct worker *worker, struct work_struct *work)
#endif
/* claim and process */
debug_work_deactivate(work);
hlist_add_head(&worker->hentry, bwh);
worker->current_work = work;
work_color = get_work_color(work);
list_del_init(&work->entry);
@ -727,6 +843,7 @@ static void process_one_work(struct worker *worker, struct work_struct *work)
spin_lock_irq(&gcwq->lock);
/* we're done with it, release */
hlist_del_init(&worker->hentry);
worker->current_work = NULL;
cwq_dec_nr_in_flight(cwq, work_color);
}
@ -763,47 +880,56 @@ static int worker_thread(void *__worker)
struct worker *worker = __worker;
struct global_cwq *gcwq = worker->gcwq;
struct cpu_workqueue_struct *cwq = worker->cwq;
DEFINE_WAIT(wait);
for (;;) {
prepare_to_wait(&cwq->more_work, &wait, TASK_INTERRUPTIBLE);
if (!kthread_should_stop() &&
list_empty(&cwq->worklist))
schedule();
finish_wait(&cwq->more_work, &wait);
woke_up:
if (unlikely(!cpumask_equal(&worker->task->cpus_allowed,
get_cpu_mask(gcwq->cpu))))
set_cpus_allowed_ptr(worker->task, get_cpu_mask(gcwq->cpu));
if (kthread_should_stop())
break;
if (unlikely(!cpumask_equal(&worker->task->cpus_allowed,
get_cpu_mask(gcwq->cpu))))
set_cpus_allowed_ptr(worker->task,
get_cpu_mask(gcwq->cpu));
spin_lock_irq(&gcwq->lock);
while (!list_empty(&cwq->worklist)) {
struct work_struct *work =
list_first_entry(&cwq->worklist,
struct work_struct, entry);
if (likely(!(*work_data_bits(work) &
WORK_STRUCT_LINKED))) {
/* optimization path, not strictly necessary */
process_one_work(worker, work);
if (unlikely(!list_empty(&worker->scheduled)))
process_scheduled_works(worker);
} else {
move_linked_works(work, &worker->scheduled,
NULL);
process_scheduled_works(worker);
}
}
spin_lock_irq(&gcwq->lock);
/* DIE can be set only while we're idle, checking here is enough */
if (worker->flags & WORKER_DIE) {
spin_unlock_irq(&gcwq->lock);
return 0;
}
return 0;
worker_leave_idle(worker);
/*
* ->scheduled list can only be filled while a worker is
* preparing to process a work or actually processing it.
* Make sure nobody diddled with it while I was sleeping.
*/
BUG_ON(!list_empty(&worker->scheduled));
while (!list_empty(&cwq->worklist)) {
struct work_struct *work =
list_first_entry(&cwq->worklist,
struct work_struct, entry);
if (likely(!(*work_data_bits(work) & WORK_STRUCT_LINKED))) {
/* optimization path, not strictly necessary */
process_one_work(worker, work);
if (unlikely(!list_empty(&worker->scheduled)))
process_scheduled_works(worker);
} else {
move_linked_works(work, &worker->scheduled, NULL);
process_scheduled_works(worker);
}
}
/*
* gcwq->lock is held and there's no work to process, sleep.
* Workers are woken up only while holding gcwq->lock, so
* setting the current state before releasing gcwq->lock is
* enough to prevent losing any event.
*/
worker_enter_idle(worker);
__set_current_state(TASK_INTERRUPTIBLE);
spin_unlock_irq(&gcwq->lock);
schedule();
goto woke_up;
}
struct wq_barrier {
@ -1600,7 +1726,6 @@ struct workqueue_struct *__create_workqueue_key(const char *name,
cwq->max_active = max_active;
INIT_LIST_HEAD(&cwq->worklist);
INIT_LIST_HEAD(&cwq->delayed_works);
init_waitqueue_head(&cwq->more_work);
if (failed)
continue;
@ -1651,7 +1776,7 @@ EXPORT_SYMBOL_GPL(__create_workqueue_key);
*/
void destroy_workqueue(struct workqueue_struct *wq)
{
int cpu;
unsigned int cpu;
flush_workqueue(wq);
@ -1670,8 +1795,10 @@ void destroy_workqueue(struct workqueue_struct *wq)
int i;
if (cwq->worker) {
spin_lock_irq(&cwq->gcwq->lock);
destroy_worker(cwq->worker);
cwq->worker = NULL;
spin_unlock_irq(&cwq->gcwq->lock);
}
for (i = 0; i < WORK_NR_COLORS; i++)
@ -1881,7 +2008,7 @@ void thaw_workqueues(void)
cwq->nr_active < cwq->max_active)
cwq_activate_first_delayed(cwq);
wake_up(&cwq->more_work);
wake_up_process(cwq->worker->task);
}
spin_unlock_irq(&gcwq->lock);
@ -1896,6 +2023,7 @@ void thaw_workqueues(void)
void __init init_workqueues(void)
{
unsigned int cpu;
int i;
singlethread_cpu = cpumask_first(cpu_possible_mask);
hotcpu_notifier(workqueue_cpu_callback, 0);
@ -1907,6 +2035,10 @@ void __init init_workqueues(void)
spin_lock_init(&gcwq->lock);
gcwq->cpu = cpu;
INIT_LIST_HEAD(&gcwq->idle_list);
for (i = 0; i < BUSY_WORKER_HASH_SIZE; i++)
INIT_HLIST_HEAD(&gcwq->busy_hash[i]);
ida_init(&gcwq->worker_ida);
}