[PATCH 2/3] workqueue: Maintain pwq->total_in_flight

[Tejun Heo]

pwq_busy() scans all of pwq->nr_in_flight[] to tell whether anything is in
flight. Maintain the sum in pwq->total_in_flight, which fits in existing
padding, and test that instead.

Signed-off-by: Tejun Heo <tj@xxxxxxxxxx>
---
 kernel/workqueue.c | 29 ++++++++++++++++++++++-------
 1 file changed, 22 insertions(+), 7 deletions(-)

diff --git a/kernel/workqueue.c b/kernel/workqueue.c
index 9c69efcf5e2e..d19d2e59ec05 100644
--- a/kernel/workqueue.c
+++ b/kernel/workqueue.c
@@ -274,6 +274,7 @@ struct pool_workqueue {
 	int			work_color;	/* L: current color */
 	int			flush_color;	/* L: flushing color */
 	int			refcnt;		/* L: reference count */
+	int			total_in_flight; /* L: sum of nr_in_flight[] */
 	int			nr_in_flight[WORK_NR_COLORS];
 						/* L: nr of in_flight works */
 	bool			plugged;	/* L: execution suspended */
@@ -2082,6 +2083,22 @@ static void pwq_dec_nr_active(struct pool_workqueue *pwq)
 		node_activate_pending_pwq(nna, pool);
 }
 
+/**
+ * pwq_inc_nr_in_flight - increment pwq's nr_in_flight
+ * @pwq: pwq of interest
+ * @work_color: color of the work item being queued
+ *
+ * A work item or a barrier with @work_color is being queued to @pwq.
+ *
+ * CONTEXT:
+ * raw_spin_lock_irq(pool->lock).
+ */
+static void pwq_inc_nr_in_flight(struct pool_workqueue *pwq, int work_color)
+{
+	pwq->nr_in_flight[work_color]++;
+	pwq->total_in_flight++;
+}
+
 /**
  * pwq_dec_nr_in_flight - decrement pwq's nr_in_flight
  * @pwq: pwq of interest
@@ -2106,6 +2123,7 @@ static void pwq_dec_nr_in_flight(struct pool_workqueue *pwq, unsigned long work_
 		pwq_dec_nr_active(pwq);
 
 	pwq->nr_in_flight[color]--;
+	pwq->total_in_flight--;
 
 	/* is flush in progress and are we at the flushing tip? */
 	if (likely(pwq->flush_color != color))
@@ -2455,7 +2473,7 @@ static void __queue_work(int cpu, struct workqueue_struct *wq,
 	if (WARN_ON(!list_empty(&work->entry)))
 		goto out;
 
-	pwq->nr_in_flight[pwq->work_color]++;
+	pwq_inc_nr_in_flight(pwq, pwq->work_color);
 	work_flags = work_color_to_flags(pwq->work_color);
 
 	/*
@@ -4031,7 +4049,7 @@ static void insert_wq_barrier(struct pool_workqueue *pwq,
 		__set_bit(WORK_STRUCT_LINKED_BIT, bits);
 	}
 
-	pwq->nr_in_flight[work_color]++;
+	pwq_inc_nr_in_flight(pwq, work_color);
 	work_flags |= work_color_to_flags(work_color);
 
 	insert_work(pwq, &barr->work, head, work_flags);
@@ -6098,11 +6116,8 @@ EXPORT_SYMBOL_GPL(alloc_workqueue_lockdep_map);
 
 static bool pwq_busy(struct pool_workqueue *pwq)
 {
-	int i;
-
-	for (i = 0; i < WORK_NR_COLORS; i++)
-		if (pwq->nr_in_flight[i])
-			return true;
+	if (pwq->total_in_flight)
+		return true;
 
 	if ((pwq != rcu_access_pointer(pwq->wq->dfl_pwq)) && (pwq->refcnt > 1))
 		return true;
-- 
2.55.0