[PATCH 16/30] workqueue: introduce global cwq and unify cwq locks

From: Tejun Heo
Date: Mon Jun 14 2010 - 17:42:48 EST

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There is one gcwq (global cwq) per each cpu and all cwqs on an cpu
point to it. A gcwq contains a lock to be used by all cwqs on the cpu
and an ida to give IDs to workers belonging to the cpu.

This patch introduces gcwq, moves worker_ida into gcwq and make all
cwqs on the same cpu use the cpu's gcwq->lock instead of separate
locks. gcwq->ida is now protected by gcwq->lock too.

Signed-off-by: Tejun Heo <tj@xxxxxxxxxx>
---
kernel/workqueue.c | 160 ++++++++++++++++++++++++++++++++--------------------
1 files changed, 98 insertions(+), 62 deletions(-)

diff --git a/kernel/workqueue.c b/kernel/workqueue.c
index 44c0fb2..d0ca750 100644
--- a/kernel/workqueue.c
+++ b/kernel/workqueue.c
@@ -40,38 +40,45 @@
*
* I: Set during initialization and read-only afterwards.
*
- * L: cwq->lock protected. Access with cwq->lock held.
+ * L: gcwq->lock protected. Access with gcwq->lock held.
*
* F: wq->flush_mutex protected.
*
* W: workqueue_lock protected.
*/

+struct global_cwq;
struct cpu_workqueue_struct;

struct worker {
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 */
int id; /* I: worker id */
};

/*
+ * Global per-cpu workqueue.
+ */
+struct global_cwq {
+ spinlock_t lock; /* the gcwq lock */
+ unsigned int cpu; /* I: the associated cpu */
+ struct ida worker_ida; /* L: for worker IDs */
+} ____cacheline_aligned_in_smp;
+
+/*
* The per-CPU workqueue (if single thread, we always use the first
* possible cpu). The lower WORK_STRUCT_FLAG_BITS of
* work_struct->data are used for flags and thus cwqs need to be
* aligned at two's power of the number of flag bits.
*/
struct cpu_workqueue_struct {
-
- spinlock_t lock;
-
+ struct global_cwq *gcwq; /* I: the associated gcwq */
struct list_head worklist;
wait_queue_head_t more_work;
- unsigned int cpu;
struct worker *worker;
-
struct workqueue_struct *wq; /* I: the owning workqueue */
int work_color; /* L: current color */
int flush_color; /* L: flushing color */
@@ -228,13 +235,19 @@ static inline void debug_work_deactivate(struct work_struct *work) { }
/* Serializes the accesses to the list of workqueues. */
static DEFINE_SPINLOCK(workqueue_lock);
static LIST_HEAD(workqueues);
-static DEFINE_PER_CPU(struct ida, worker_ida);
static bool workqueue_freezing; /* W: have wqs started freezing? */

+static DEFINE_PER_CPU(struct global_cwq, global_cwq);
+
static int worker_thread(void *__worker);

static int singlethread_cpu __read_mostly;

+static struct global_cwq *get_gcwq(unsigned int cpu)
+{
+ return &per_cpu(global_cwq, cpu);
+}
+
static struct cpu_workqueue_struct *get_cwq(unsigned int cpu,
struct workqueue_struct *wq)
{
@@ -303,7 +316,7 @@ static inline struct cpu_workqueue_struct *get_wq_data(struct work_struct *work)
* Insert @work into @cwq after @head.
*
* CONTEXT:
- * spin_lock_irq(cwq->lock).
+ * spin_lock_irq(gcwq->lock).
*/
static void insert_work(struct cpu_workqueue_struct *cwq,
struct work_struct *work, struct list_head *head,
@@ -326,12 +339,13 @@ static void __queue_work(unsigned int cpu, struct workqueue_struct *wq,
struct work_struct *work)
{
struct cpu_workqueue_struct *cwq = target_cwq(cpu, wq);
+ struct global_cwq *gcwq = cwq->gcwq;
struct list_head *worklist;
unsigned long flags;

debug_work_activate(work);

- spin_lock_irqsave(&cwq->lock, flags);
+ spin_lock_irqsave(&gcwq->lock, flags);
BUG_ON(!list_empty(&work->entry));

cwq->nr_in_flight[cwq->work_color]++;
@@ -344,7 +358,7 @@ static void __queue_work(unsigned int cpu, struct workqueue_struct *wq,

insert_work(cwq, work, worklist, work_color_to_flags(cwq->work_color));

- spin_unlock_irqrestore(&cwq->lock, flags);
+ spin_unlock_irqrestore(&gcwq->lock, flags);
}

/**
@@ -483,39 +497,41 @@ static struct worker *alloc_worker(void)
*/
static struct worker *create_worker(struct cpu_workqueue_struct *cwq, bool bind)
{
+ struct global_cwq *gcwq = cwq->gcwq;
int id = -1;
struct worker *worker = NULL;

- spin_lock(&workqueue_lock);
- while (ida_get_new(&per_cpu(worker_ida, cwq->cpu), &id)) {
- spin_unlock(&workqueue_lock);
- if (!ida_pre_get(&per_cpu(worker_ida, cwq->cpu), GFP_KERNEL))
+ spin_lock_irq(&gcwq->lock);
+ while (ida_get_new(&gcwq->worker_ida, &id)) {
+ spin_unlock_irq(&gcwq->lock);
+ if (!ida_pre_get(&gcwq->worker_ida, GFP_KERNEL))
goto fail;
- spin_lock(&workqueue_lock);
+ spin_lock_irq(&gcwq->lock);
}
- spin_unlock(&workqueue_lock);
+ spin_unlock_irq(&gcwq->lock);

worker = alloc_worker();
if (!worker)
goto fail;

+ worker->gcwq = gcwq;
worker->cwq = cwq;
worker->id = id;

worker->task = kthread_create(worker_thread, worker, "kworker/%u:%d",
- cwq->cpu, id);
+ gcwq->cpu, id);
if (IS_ERR(worker->task))
goto fail;

if (bind)
- kthread_bind(worker->task, cwq->cpu);
+ kthread_bind(worker->task, gcwq->cpu);

return worker;
fail:
if (id >= 0) {
- spin_lock(&workqueue_lock);
- ida_remove(&per_cpu(worker_ida, cwq->cpu), id);
- spin_unlock(&workqueue_lock);
+ spin_lock_irq(&gcwq->lock);
+ ida_remove(&gcwq->worker_ida, id);
+ spin_unlock_irq(&gcwq->lock);
}
kfree(worker);
return NULL;
@@ -528,7 +544,7 @@ fail:
* Start @worker.
*
* CONTEXT:
- * spin_lock_irq(cwq->lock).
+ * spin_lock_irq(gcwq->lock).
*/
static void start_worker(struct worker *worker)
{
@@ -543,7 +559,7 @@ static void start_worker(struct worker *worker)
*/
static void destroy_worker(struct worker *worker)
{
- int cpu = worker->cwq->cpu;
+ struct global_cwq *gcwq = worker->gcwq;
int id = worker->id;

/* sanity check frenzy */
@@ -553,9 +569,9 @@ static void destroy_worker(struct worker *worker)
kthread_stop(worker->task);
kfree(worker);

- spin_lock(&workqueue_lock);
- ida_remove(&per_cpu(worker_ida, cpu), id);
- spin_unlock(&workqueue_lock);
+ spin_lock_irq(&gcwq->lock);
+ ida_remove(&gcwq->worker_ida, id);
+ spin_unlock_irq(&gcwq->lock);
}

/**
@@ -573,7 +589,7 @@ static void destroy_worker(struct worker *worker)
* nested inside outer list_for_each_entry_safe().
*
* CONTEXT:
- * spin_lock_irq(cwq->lock).
+ * spin_lock_irq(gcwq->lock).
*/
static void move_linked_works(struct work_struct *work, struct list_head *head,
struct work_struct **nextp)
@@ -617,7 +633,7 @@ static void cwq_activate_first_delayed(struct cpu_workqueue_struct *cwq)
* decrement nr_in_flight of its cwq and handle workqueue flushing.
*
* CONTEXT:
- * spin_lock_irq(cwq->lock).
+ * spin_lock_irq(gcwq->lock).
*/
static void cwq_dec_nr_in_flight(struct cpu_workqueue_struct *cwq, int color)
{
@@ -664,11 +680,12 @@ static void cwq_dec_nr_in_flight(struct cpu_workqueue_struct *cwq, int color)
* call this function to process a work.
*
* CONTEXT:
- * spin_lock_irq(cwq->lock) which is released and regrabbed.
+ * spin_lock_irq(gcwq->lock) which is released and regrabbed.
*/
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;
work_func_t f = work->func;
int work_color;
#ifdef CONFIG_LOCKDEP
@@ -687,7 +704,7 @@ static void process_one_work(struct worker *worker, struct work_struct *work)
work_color = get_work_color(work);
list_del_init(&work->entry);

- spin_unlock_irq(&cwq->lock);
+ spin_unlock_irq(&gcwq->lock);

BUG_ON(get_wq_data(work) != cwq);
work_clear_pending(work);
@@ -707,7 +724,7 @@ static void process_one_work(struct worker *worker, struct work_struct *work)
dump_stack();
}

- spin_lock_irq(&cwq->lock);
+ spin_lock_irq(&gcwq->lock);

/* we're done with it, release */
worker->current_work = NULL;
@@ -723,7 +740,7 @@ static void process_one_work(struct worker *worker, struct work_struct *work)
* fetches a work from the top and executes it.
*
* CONTEXT:
- * spin_lock_irq(cwq->lock) which may be released and regrabbed
+ * spin_lock_irq(gcwq->lock) which may be released and regrabbed
* multiple times.
*/
static void process_scheduled_works(struct worker *worker)
@@ -744,6 +761,7 @@ static void process_scheduled_works(struct worker *worker)
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);

@@ -758,11 +776,11 @@ static int worker_thread(void *__worker)
break;

if (unlikely(!cpumask_equal(&worker->task->cpus_allowed,
- get_cpu_mask(cwq->cpu))))
+ get_cpu_mask(gcwq->cpu))))
set_cpus_allowed_ptr(worker->task,
- get_cpu_mask(cwq->cpu));
+ get_cpu_mask(gcwq->cpu));

- spin_lock_irq(&cwq->lock);
+ spin_lock_irq(&gcwq->lock);

while (!list_empty(&cwq->worklist)) {
struct work_struct *work =
@@ -782,7 +800,7 @@ static int worker_thread(void *__worker)
}
}

- spin_unlock_irq(&cwq->lock);
+ spin_unlock_irq(&gcwq->lock);
}

return 0;
@@ -821,7 +839,7 @@ static void wq_barrier_func(struct work_struct *work)
* underneath us, so we can't reliably determine cwq from @target.
*
* CONTEXT:
- * spin_lock_irq(cwq->lock).
+ * spin_lock_irq(gcwq->lock).
*/
static void insert_wq_barrier(struct cpu_workqueue_struct *cwq,
struct wq_barrier *barr,
@@ -831,7 +849,7 @@ static void insert_wq_barrier(struct cpu_workqueue_struct *cwq,
unsigned int linked = 0;

/*
- * debugobject calls are safe here even with cwq->lock locked
+ * debugobject calls are safe here even with gcwq->lock locked
* as we know for sure that this will not trigger any of the
* checks and call back into the fixup functions where we
* might deadlock.
@@ -904,8 +922,9 @@ static bool flush_workqueue_prep_cwqs(struct workqueue_struct *wq,

for_each_possible_cpu(cpu) {
struct cpu_workqueue_struct *cwq = get_cwq(cpu, wq);
+ struct global_cwq *gcwq = cwq->gcwq;

- spin_lock_irq(&cwq->lock);
+ spin_lock_irq(&gcwq->lock);

if (flush_color >= 0) {
BUG_ON(cwq->flush_color != -1);
@@ -922,7 +941,7 @@ static bool flush_workqueue_prep_cwqs(struct workqueue_struct *wq,
cwq->work_color = work_color;
}

- spin_unlock_irq(&cwq->lock);
+ spin_unlock_irq(&gcwq->lock);
}

if (flush_color >= 0 && atomic_dec_and_test(&wq->nr_cwqs_to_flush))
@@ -1097,17 +1116,19 @@ int flush_work(struct work_struct *work)
{
struct worker *worker = NULL;
struct cpu_workqueue_struct *cwq;
+ struct global_cwq *gcwq;
struct wq_barrier barr;

might_sleep();
cwq = get_wq_data(work);
if (!cwq)
return 0;
+ gcwq = cwq->gcwq;

lock_map_acquire(&cwq->wq->lockdep_map);
lock_map_release(&cwq->wq->lockdep_map);

- spin_lock_irq(&cwq->lock);
+ spin_lock_irq(&gcwq->lock);
if (!list_empty(&work->entry)) {
/*
* See the comment near try_to_grab_pending()->smp_rmb().
@@ -1124,12 +1145,12 @@ int flush_work(struct work_struct *work)
}

insert_wq_barrier(cwq, &barr, work, worker);
- spin_unlock_irq(&cwq->lock);
+ spin_unlock_irq(&gcwq->lock);
wait_for_completion(&barr.done);
destroy_work_on_stack(&barr.work);
return 1;
already_gone:
- spin_unlock_irq(&cwq->lock);
+ spin_unlock_irq(&gcwq->lock);
return 0;
}
EXPORT_SYMBOL_GPL(flush_work);
@@ -1140,6 +1161,7 @@ EXPORT_SYMBOL_GPL(flush_work);
*/
static int try_to_grab_pending(struct work_struct *work)
{
+ struct global_cwq *gcwq;
struct cpu_workqueue_struct *cwq;
int ret = -1;

@@ -1154,8 +1176,9 @@ static int try_to_grab_pending(struct work_struct *work)
cwq = get_wq_data(work);
if (!cwq)
return ret;
+ gcwq = cwq->gcwq;

- spin_lock_irq(&cwq->lock);
+ spin_lock_irq(&gcwq->lock);
if (!list_empty(&work->entry)) {
/*
* This work is queued, but perhaps we locked the wrong cwq.
@@ -1170,7 +1193,7 @@ static int try_to_grab_pending(struct work_struct *work)
ret = 1;
}
}
- spin_unlock_irq(&cwq->lock);
+ spin_unlock_irq(&gcwq->lock);

return ret;
}
@@ -1178,10 +1201,11 @@ static int try_to_grab_pending(struct work_struct *work)
static void wait_on_cpu_work(struct cpu_workqueue_struct *cwq,
struct work_struct *work)
{
+ struct global_cwq *gcwq = cwq->gcwq;
struct wq_barrier barr;
struct worker *worker;

- spin_lock_irq(&cwq->lock);
+ spin_lock_irq(&gcwq->lock);

worker = NULL;
if (unlikely(cwq->worker && cwq->worker->current_work == work)) {
@@ -1189,7 +1213,7 @@ static void wait_on_cpu_work(struct cpu_workqueue_struct *cwq,
insert_wq_barrier(cwq, &barr, work, worker);
}

- spin_unlock_irq(&cwq->lock);
+ spin_unlock_irq(&gcwq->lock);

if (unlikely(worker)) {
wait_for_completion(&barr.done);
@@ -1561,13 +1585,13 @@ struct workqueue_struct *__create_workqueue_key(const char *name,
*/
for_each_possible_cpu(cpu) {
struct cpu_workqueue_struct *cwq = get_cwq(cpu, wq);
+ struct global_cwq *gcwq = get_gcwq(cpu);

BUG_ON((unsigned long)cwq & WORK_STRUCT_FLAG_MASK);
- cwq->cpu = cpu;
+ cwq->gcwq = gcwq;
cwq->wq = wq;
cwq->flush_color = -1;
cwq->max_active = max_active;
- spin_lock_init(&cwq->lock);
INIT_LIST_HEAD(&cwq->worklist);
INIT_LIST_HEAD(&cwq->delayed_works);
init_waitqueue_head(&cwq->more_work);
@@ -1738,7 +1762,7 @@ EXPORT_SYMBOL_GPL(work_on_cpu);
* list instead of the cwq ones.
*
* CONTEXT:
- * Grabs and releases workqueue_lock and cwq->lock's.
+ * Grabs and releases workqueue_lock and gcwq->lock's.
*/
void freeze_workqueues_begin(void)
{
@@ -1751,16 +1775,18 @@ void freeze_workqueues_begin(void)
workqueue_freezing = true;

for_each_possible_cpu(cpu) {
+ struct global_cwq *gcwq = get_gcwq(cpu);
+
+ spin_lock_irq(&gcwq->lock);
+
list_for_each_entry(wq, &workqueues, list) {
struct cpu_workqueue_struct *cwq = get_cwq(cpu, wq);

- spin_lock_irq(&cwq->lock);
-
if (wq->flags & WQ_FREEZEABLE)
cwq->max_active = 0;
-
- spin_unlock_irq(&cwq->lock);
}
+
+ spin_unlock_irq(&gcwq->lock);
}

spin_unlock(&workqueue_lock);
@@ -1819,7 +1845,7 @@ out_unlock:
* frozen works are transferred to their respective cwq worklists.
*
* CONTEXT:
- * Grabs and releases workqueue_lock and cwq->lock's.
+ * Grabs and releases workqueue_lock and gcwq->lock's.
*/
void thaw_workqueues(void)
{
@@ -1832,14 +1858,16 @@ void thaw_workqueues(void)
goto out_unlock;

for_each_possible_cpu(cpu) {
+ struct global_cwq *gcwq = get_gcwq(cpu);
+
+ spin_lock_irq(&gcwq->lock);
+
list_for_each_entry(wq, &workqueues, list) {
struct cpu_workqueue_struct *cwq = get_cwq(cpu, wq);

if (!(wq->flags & WQ_FREEZEABLE))
continue;

- spin_lock_irq(&cwq->lock);
-
/* restore max_active and repopulate worklist */
cwq->max_active = wq->saved_max_active;

@@ -1848,9 +1876,9 @@ void thaw_workqueues(void)
cwq_activate_first_delayed(cwq);

wake_up(&cwq->more_work);
-
- spin_unlock_irq(&cwq->lock);
}
+
+ spin_unlock_irq(&gcwq->lock);
}

workqueue_freezing = false;
@@ -1871,11 +1899,19 @@ void __init init_workqueues(void)
BUILD_BUG_ON(__alignof__(struct cpu_workqueue_struct) <
__alignof__(unsigned long long));

- for_each_possible_cpu(cpu)
- ida_init(&per_cpu(worker_ida, cpu));
-
singlethread_cpu = cpumask_first(cpu_possible_mask);
hotcpu_notifier(workqueue_cpu_callback, 0);
+
+ /* initialize gcwqs */
+ for_each_possible_cpu(cpu) {
+ struct global_cwq *gcwq = get_gcwq(cpu);
+
+ spin_lock_init(&gcwq->lock);
+ gcwq->cpu = cpu;
+
+ ida_init(&gcwq->worker_ida);
+ }
+
keventd_wq = create_workqueue("events");
BUG_ON(!keventd_wq);
}
--
1.6.4.2

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Next message: Tejun Heo: "[PATCH 09/30] workqueue: kill cpu_populated_map"
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Next in thread: Tejun Heo: "[PATCH 09/30] workqueue: kill cpu_populated_map"
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