workqueue: introduce global cwq and unify cwq locks

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@kernel.org>

1 files changed, 98 insertions, 62 deletions

diff --git a/kernel/workqueue.c b/kernel/workqueue.c
index 4d059c532792..b043f57516bd 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);
@@ -1567,13 +1591,13 @@ 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);
@@ -1744,7 +1768,7 @@ 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)
 {
@@ -1757,16 +1781,18 @@ 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);
@@ -1825,7 +1851,7 @@ 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)
 {
@@ -1838,14 +1864,16 @@ 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;
 
@@ -1854,9 +1882,9 @@ 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;
@@ -1869,11 +1897,19 @@ void __init init_workqueues(void)
 {
         unsigned int cpu;
 
-        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);
 }