workqueue: introduce cpu_singlethread_map

The code like

	if (is_single_threaded(wq))
		do_something(singlethread_cpu);
	else {
		for_each_cpu_mask(cpu, cpu_populated_map)
			do_something(cpu);
	}

looks very annoying. We can add "static cpumask_t cpu_singlethread_map" and
simplify the code. Lessens .text a bit, and imho makes the code more readable.
Signed-off-by: Oleg Nesterov <oleg@tv-sign.ru>
Cc: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

kernel/workqueue.c

@@ -69,6 +69,7 @@ static DEFINE_MUTEX(workqueue_mutex);
 static LIST_HEAD(workqueues);
 
 static int singlethread_cpu __read_mostly;
+static cpumask_t cpu_singlethread_map __read_mostly;
 /* optimization, we could use cpu_possible_map */
 static cpumask_t cpu_populated_map __read_mostly;
 
@@ -78,6 +79,12 @@ static inline int is_single_threaded(struct workqueue_struct *wq)
 	return list_empty(&wq->list);
 }
 
+static const cpumask_t *wq_cpu_map(struct workqueue_struct *wq)
+{
+	return is_single_threaded(wq)
+		? &cpu_singlethread_map : &cpu_populated_map;
+}
+
 /*
  * Set the workqueue on which a work item is to be run
  * - Must *only* be called if the pending flag is set
@@ -393,16 +400,12 @@ static void flush_cpu_workqueue(struct cpu_workqueue_struct *cwq)
  */
 void fastcall flush_workqueue(struct workqueue_struct *wq)
 {
-	might_sleep();
+	const cpumask_t *cpu_map = wq_cpu_map(wq);
+	int cpu
 
-	if (is_single_threaded(wq))
-		flush_cpu_workqueue(per_cpu_ptr(wq->cpu_wq, singlethread_cpu));
-	else {
-		int cpu;
-
-		for_each_cpu_mask(cpu, cpu_populated_map)
+	might_sleep();
+	for_each_cpu_mask(cpu, *cpu_map)
 		flush_cpu_workqueue(per_cpu_ptr(wq->cpu_wq, cpu));
-	}
 }
 EXPORT_SYMBOL_GPL(flush_workqueue);
 
@@ -439,7 +442,9 @@ static void wait_on_work(struct cpu_workqueue_struct *cwq,
  */
 void flush_work(struct workqueue_struct *wq, struct work_struct *work)
 {
+	const cpumask_t *cpu_map = wq_cpu_map(wq);
 	struct cpu_workqueue_struct *cwq;
+	int cpu;
 
 	might_sleep();
 
@@ -457,14 +462,8 @@ void flush_work(struct workqueue_struct *wq, struct work_struct *work)
 	work_release(work);
 	spin_unlock_irq(&cwq->lock);
 
-	if (is_single_threaded(wq))
-		wait_on_work(per_cpu_ptr(wq->cpu_wq, singlethread_cpu), work);
-	else {
-		int cpu;
-
-		for_each_cpu_mask(cpu, cpu_populated_map)
+	for_each_cpu_mask(cpu, *cpu_map)
 		wait_on_work(per_cpu_ptr(wq->cpu_wq, cpu), work);
-	}
 }
 EXPORT_SYMBOL_GPL(flush_work);
 
@@ -757,23 +756,18 @@ static void cleanup_workqueue_thread(struct cpu_workqueue_struct *cwq, int cpu)
  */
 void destroy_workqueue(struct workqueue_struct *wq)
 {
+	const cpumask_t *cpu_map = wq_cpu_map(wq);
 	struct cpu_workqueue_struct *cwq;
-
-	if (is_single_threaded(wq)) {
-		cwq = per_cpu_ptr(wq->cpu_wq, singlethread_cpu);
-		cleanup_workqueue_thread(cwq, singlethread_cpu);
-	} else {
 	int cpu;
 
 	mutex_lock(&workqueue_mutex);
 	list_del(&wq->list);
 	mutex_unlock(&workqueue_mutex);
 
-		for_each_cpu_mask(cpu, cpu_populated_map) {
+	for_each_cpu_mask(cpu, *cpu_map) {
 		cwq = per_cpu_ptr(wq->cpu_wq, cpu);
 		cleanup_workqueue_thread(cwq, cpu);
 	}
-	}
 
 	free_percpu(wq->cpu_wq);
 	kfree(wq);
@@ -831,6 +825,7 @@ void init_workqueues(void)
 {
 	cpu_populated_map = cpu_online_map;
 	singlethread_cpu = first_cpu(cpu_possible_map);
+	cpu_singlethread_map = cpumask_of_cpu(singlethread_cpu);
 	hotcpu_notifier(workqueue_cpu_callback, 0);
 	keventd_wq = create_workqueue("events");
 	BUG_ON(!keventd_wq);