---

yaml
---
r: 206221
b: refs/heads/master
c: 502ca9d
h: refs/heads/master
i:
  206219: 10aa972
v: v3

[refs]

@@ -1,2 +1,2 @@
 ---
-refs/heads/master: db7bccf45cb87522096b8f43144e31ca605a9f24
+refs/heads/master: 502ca9d819792e7d79b6e002afe9094c641fe410

trunk/include/linux/workqueue.h

@@ -221,7 +221,7 @@ static inline unsigned int work_static(struct work_struct *work) { return 0; }
 
 enum {
 	WQ_FREEZEABLE		= 1 << 0, /* freeze during suspend */
-	WQ_SINGLE_THREAD	= 1 << 1, /* no per-cpu worker */
+	WQ_SINGLE_CPU		= 1 << 1, /* only single cpu at a time */
 };
 
 extern struct workqueue_struct *
@@ -250,9 +250,9 @@ __create_workqueue_key(const char *name, unsigned int flags, int max_active,
 #define create_workqueue(name)					\
 	__create_workqueue((name), 0, 1)
 #define create_freezeable_workqueue(name)			\
-	__create_workqueue((name), WQ_FREEZEABLE | WQ_SINGLE_THREAD, 1)
+	__create_workqueue((name), WQ_FREEZEABLE | WQ_SINGLE_CPU, 1)
 #define create_singlethread_workqueue(name)			\
-	__create_workqueue((name), WQ_SINGLE_THREAD, 1)
+	__create_workqueue((name), WQ_SINGLE_CPU, 1)
 
 extern void destroy_workqueue(struct workqueue_struct *wq);
 

trunk/kernel/workqueue.c

@@ -114,8 +114,7 @@ struct global_cwq {
 } ____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
+ * The per-CPU workqueue.  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.
  */
@@ -159,6 +158,8 @@ struct workqueue_struct {
 	struct list_head	flusher_queue;	/* F: flush waiters */
 	struct list_head	flusher_overflow; /* F: flush overflow list */
 
+	unsigned long		single_cpu;	/* cpu for single cpu wq */
+
 	int			saved_max_active; /* I: saved cwq max_active */
 	const char		*name;		/* I: workqueue name */
 #ifdef CONFIG_LOCKDEP
@@ -289,8 +290,6 @@ 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);
@@ -302,14 +301,6 @@ static struct cpu_workqueue_struct *get_cwq(unsigned int cpu,
 	return per_cpu_ptr(wq->cpu_wq, cpu);
 }
 
-static struct cpu_workqueue_struct *target_cwq(unsigned int cpu,
-					       struct workqueue_struct *wq)
-{
-	if (unlikely(wq->flags & WQ_SINGLE_THREAD))
-		cpu = singlethread_cpu;
-	return get_cwq(cpu, wq);
-}
-
 static unsigned int work_color_to_flags(int color)
 {
 	return color << WORK_STRUCT_COLOR_SHIFT;
@@ -410,17 +401,87 @@ static void insert_work(struct cpu_workqueue_struct *cwq,
 	wake_up_process(cwq->worker->task);
 }
 
+/**
+ * cwq_unbind_single_cpu - unbind cwq from single cpu workqueue processing
+ * @cwq: cwq to unbind
+ *
+ * Try to unbind @cwq from single cpu workqueue processing.  If
+ * @cwq->wq is frozen, unbind is delayed till the workqueue is thawed.
+ *
+ * CONTEXT:
+ * spin_lock_irq(gcwq->lock).
+ */
+static void cwq_unbind_single_cpu(struct cpu_workqueue_struct *cwq)
+{
+	struct workqueue_struct *wq = cwq->wq;
+	struct global_cwq *gcwq = cwq->gcwq;
+
+	BUG_ON(wq->single_cpu != gcwq->cpu);
+	/*
+	 * Unbind from workqueue if @cwq is not frozen.  If frozen,
+	 * thaw_workqueues() will either restart processing on this
+	 * cpu or unbind if empty.  This keeps works queued while
+	 * frozen fully ordered and flushable.
+	 */
+	if (likely(!(gcwq->flags & GCWQ_FREEZING))) {
+		smp_wmb();	/* paired with cmpxchg() in __queue_work() */
+		wq->single_cpu = NR_CPUS;
+	}
+}
+
 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 global_cwq *gcwq;
+	struct cpu_workqueue_struct *cwq;
 	struct list_head *worklist;
 	unsigned long flags;
+	bool arbitrate;
 
 	debug_work_activate(work);
 
-	spin_lock_irqsave(&gcwq->lock, flags);
+	/* determine gcwq to use */
+	if (!(wq->flags & WQ_SINGLE_CPU)) {
+		/* just use the requested cpu for multicpu workqueues */
+		gcwq = get_gcwq(cpu);
+		spin_lock_irqsave(&gcwq->lock, flags);
+	} else {
+		unsigned int req_cpu = cpu;
+
+		/*
+		 * It's a bit more complex for single cpu workqueues.
+		 * We first need to determine which cpu is going to be
+		 * used.  If no cpu is currently serving this
+		 * workqueue, arbitrate using atomic accesses to
+		 * wq->single_cpu; otherwise, use the current one.
+		 */
+	retry:
+		cpu = wq->single_cpu;
+		arbitrate = cpu == NR_CPUS;
+		if (arbitrate)
+			cpu = req_cpu;
+
+		gcwq = get_gcwq(cpu);
+		spin_lock_irqsave(&gcwq->lock, flags);
+
+		/*
+		 * The following cmpxchg() is a full barrier paired
+		 * with smp_wmb() in cwq_unbind_single_cpu() and
+		 * guarantees that all changes to wq->st_* fields are
+		 * visible on the new cpu after this point.
+		 */
+		if (arbitrate)
+			cmpxchg(&wq->single_cpu, NR_CPUS, cpu);
+
+		if (unlikely(wq->single_cpu != cpu)) {
+			spin_unlock_irqrestore(&gcwq->lock, flags);
+			goto retry;
+		}
+	}
+
+	/* gcwq determined, get cwq and queue */
+	cwq = get_cwq(gcwq->cpu, wq);
+
 	BUG_ON(!list_empty(&work->entry));
 
 	cwq->nr_in_flight[cwq->work_color]++;
@@ -530,7 +591,7 @@ int queue_delayed_work_on(int cpu, struct workqueue_struct *wq,
 		timer_stats_timer_set_start_info(&dwork->timer);
 
 		/* This stores cwq for the moment, for the timer_fn */
-		set_wq_data(work, target_cwq(raw_smp_processor_id(), wq), 0);
+		set_wq_data(work, get_cwq(raw_smp_processor_id(), wq), 0);
 		timer->expires = jiffies + delay;
 		timer->data = (unsigned long)dwork;
 		timer->function = delayed_work_timer_fn;
@@ -790,10 +851,14 @@ static void cwq_dec_nr_in_flight(struct cpu_workqueue_struct *cwq, int color)
 	cwq->nr_in_flight[color]--;
 	cwq->nr_active--;
 
-	/* one down, submit a delayed one */
-	if (!list_empty(&cwq->delayed_works) &&
-	    cwq->nr_active < cwq->max_active)
-		cwq_activate_first_delayed(cwq);
+	if (!list_empty(&cwq->delayed_works)) {
+		/* one down, submit a delayed one */
+		if (cwq->nr_active < cwq->max_active)
+			cwq_activate_first_delayed(cwq);
+	} else if (!cwq->nr_active && cwq->wq->flags & WQ_SINGLE_CPU) {
+		/* this was the last work, unbind from single cpu */
+		cwq_unbind_single_cpu(cwq);
+	}
 
 	/* is flush in progress and are we at the flushing tip? */
 	if (likely(cwq->flush_color != color))
@@ -1727,7 +1792,6 @@ struct workqueue_struct *__create_workqueue_key(const char *name,
 						struct lock_class_key *key,
 						const char *lock_name)
 {
-	bool singlethread = flags & WQ_SINGLE_THREAD;
 	struct workqueue_struct *wq;
 	bool failed = false;
 	unsigned int cpu;
@@ -1748,6 +1812,8 @@ struct workqueue_struct *__create_workqueue_key(const char *name,
 	atomic_set(&wq->nr_cwqs_to_flush, 0);
 	INIT_LIST_HEAD(&wq->flusher_queue);
 	INIT_LIST_HEAD(&wq->flusher_overflow);
+	wq->single_cpu = NR_CPUS;
+
 	wq->name = name;
 	lockdep_init_map(&wq->lockdep_map, lock_name, key, 0);
 	INIT_LIST_HEAD(&wq->list);
@@ -1773,8 +1839,7 @@ struct workqueue_struct *__create_workqueue_key(const char *name,
 
 		if (failed)
 			continue;
-		cwq->worker = create_worker(cwq,
-					    cpu_online(cpu) && !singlethread);
+		cwq->worker = create_worker(cwq, cpu_online(cpu));
 		if (cwq->worker)
 			start_worker(cwq->worker);
 		else
@@ -1958,18 +2023,16 @@ static int __cpuinit trustee_thread(void *__gcwq)
 
 	spin_lock_irq(&gcwq->lock);
 	/*
-	 * Make all multithread workers rogue.  Trustee must be bound
-	 * to the target cpu and can't be cancelled.
+	 * Make all workers rogue.  Trustee must be bound to the
+	 * target cpu and can't be cancelled.
 	 */
 	BUG_ON(gcwq->cpu != smp_processor_id());
 
 	list_for_each_entry(worker, &gcwq->idle_list, entry)
-		if (!(worker->cwq->wq->flags & WQ_SINGLE_THREAD))
-			worker->flags |= WORKER_ROGUE;
+		worker->flags |= WORKER_ROGUE;
 
 	for_each_busy_worker(worker, i, pos, gcwq)
-		if (!(worker->cwq->wq->flags & WQ_SINGLE_THREAD))
-			worker->flags |= WORKER_ROGUE;
+		worker->flags |= WORKER_ROGUE;
 
 	/*
 	 * We're now in charge.  Notify and proceed to drain.  We need
@@ -2074,14 +2137,12 @@ static int __devinit workqueue_cpu_callback(struct notifier_block *nfb,
 			wait_trustee_state(gcwq, TRUSTEE_DONE);
 		}
 
-		/* clear ROGUE from all multithread workers */
+		/* clear ROGUE from all workers */
 		list_for_each_entry(worker, &gcwq->idle_list, entry)
-			if (!(worker->cwq->wq->flags & WQ_SINGLE_THREAD))
-				worker->flags &= ~WORKER_ROGUE;
+			worker->flags &= ~WORKER_ROGUE;
 
 		for_each_busy_worker(worker, i, pos, gcwq)
-			if (!(worker->cwq->wq->flags & WQ_SINGLE_THREAD))
-				worker->flags &= ~WORKER_ROGUE;
+			worker->flags &= ~WORKER_ROGUE;
 		break;
 	}
 
@@ -2266,6 +2327,11 @@ void thaw_workqueues(void)
 			       cwq->nr_active < cwq->max_active)
 				cwq_activate_first_delayed(cwq);
 
+			/* perform delayed unbind from single cpu if empty */
+			if (wq->single_cpu == gcwq->cpu &&
+			    !cwq->nr_active && list_empty(&cwq->delayed_works))
+				cwq_unbind_single_cpu(cwq);
+
 			wake_up_process(cwq->worker->task);
 		}
 
@@ -2283,7 +2349,6 @@ void __init init_workqueues(void)
 	unsigned int cpu;
 	int i;
 
-	singlethread_cpu = cpumask_first(cpu_possible_mask);
 	hotcpu_notifier(workqueue_cpu_callback, CPU_PRI_WORKQUEUE);
 
 	/* initialize gcwqs */