[PATCH] Add blk_start_queueing() helper

CFQ implements this on its own now, but it's really block layer
knowledge. Tells a device queue to start dispatching requests to
the driver, taking care to unplug if needed. Also fixes the issue
where as/cfq will invoke a stopped queue, which we really don't
want.

Signed-off-by: Jens Axboe <axboe@suse.de>

Author: Jens Axboe

block/as-iosched.c

@@ -1280,8 +1280,7 @@ static void as_work_handler(void *data)
 	unsigned long flags;
 
 	spin_lock_irqsave(q->queue_lock, flags);
-	if (!as_queue_empty(q))
-		q->request_fn(q);
+	blk_start_queueing(q);
 	spin_unlock_irqrestore(q->queue_lock, flags);
 }
 

block/cfq-iosched.c

@@ -1552,19 +1552,6 @@ static void cfq_preempt_queue(struct cfq_data *cfqd, struct cfq_queue *cfqq)
 	__cfq_set_active_queue(cfqd, cfqq);
 }
 
-/*
- * should really be a ll_rw_blk.c helper
- */
-static void cfq_start_queueing(struct cfq_data *cfqd, struct cfq_queue *cfqq)
-{
-	request_queue_t *q = cfqd->queue;
-
-	if (!blk_queue_plugged(q))
-		q->request_fn(q);
-	else
-		__generic_unplug_device(q);
-}
-
 /*
  * Called when a new fs request (rq) is added (to cfqq). Check if there's
  * something we should do about it
@@ -1593,7 +1580,7 @@ cfq_rq_enqueued(struct cfq_data *cfqd, struct cfq_queue *cfqq,
 		if (cic == cfqd->active_cic &&
 		    del_timer(&cfqd->idle_slice_timer)) {
 			cfq_slice_expired(cfqd, 0);
-			cfq_start_queueing(cfqd, cfqq);
+			blk_start_queueing(cfqd->queue);
 		}
 		return;
 	}
@@ -1614,7 +1601,7 @@ cfq_rq_enqueued(struct cfq_data *cfqd, struct cfq_queue *cfqq,
 		if (cfq_cfqq_wait_request(cfqq)) {
 			cfq_mark_cfqq_must_dispatch(cfqq);
 			del_timer(&cfqd->idle_slice_timer);
-			cfq_start_queueing(cfqd, cfqq);
+			blk_start_queueing(cfqd->queue);
 		}
 	} else if (cfq_should_preempt(cfqd, cfqq, rq)) {
 		/*
@@ -1624,7 +1611,7 @@ cfq_rq_enqueued(struct cfq_data *cfqd, struct cfq_queue *cfqq,
 		 */
 		cfq_preempt_queue(cfqd, cfqq);
 		cfq_mark_cfqq_must_dispatch(cfqq);
-		cfq_start_queueing(cfqd, cfqq);
+		blk_start_queueing(cfqd->queue);
 	}
 }
 
@@ -1832,8 +1819,7 @@ static void cfq_kick_queue(void *data)
 	unsigned long flags;
 
 	spin_lock_irqsave(q->queue_lock, flags);
-	blk_remove_plug(q);
-	q->request_fn(q);
+	blk_start_queueing(q);
 	spin_unlock_irqrestore(q->queue_lock, flags);
 }
 

block/ll_rw_blk.c

@@ -2266,6 +2266,25 @@ struct request *blk_get_request(request_queue_t *q, int rw, gfp_t gfp_mask)
 }
 EXPORT_SYMBOL(blk_get_request);
 
+/**
+ * blk_start_queueing - initiate dispatch of requests to device
+ * @q:		request queue to kick into gear
+ *
+ * This is basically a helper to remove the need to know whether a queue
+ * is plugged or not if someone just wants to initiate dispatch of requests
+ * for this queue.
+ *
+ * The queue lock must be held with interrupts disabled.
+ */
+void blk_start_queueing(request_queue_t *q)
+{
+	if (!blk_queue_plugged(q))
+		q->request_fn(q);
+	else
+		__generic_unplug_device(q);
+}
+EXPORT_SYMBOL(blk_start_queueing);
+
 /**
  * blk_requeue_request - put a request back on queue
  * @q:		request queue where request should be inserted
@@ -2333,11 +2352,7 @@ void blk_insert_request(request_queue_t *q, struct request *rq,
 
 	drive_stat_acct(rq, rq->nr_sectors, 1);
 	__elv_add_request(q, rq, where, 0);
-
-	if (blk_queue_plugged(q))
-		__generic_unplug_device(q);
-	else
-		q->request_fn(q);
+	blk_start_queueing(q);
 	spin_unlock_irqrestore(q->queue_lock, flags);
 }
 

include/linux/blkdev.h

@@ -635,6 +635,7 @@ extern void blk_stop_queue(request_queue_t *q);
 extern void blk_sync_queue(struct request_queue *q);
 extern void __blk_stop_queue(request_queue_t *q);
 extern void blk_run_queue(request_queue_t *);
+extern void blk_start_queueing(request_queue_t *);
 extern void blk_queue_activity_fn(request_queue_t *, activity_fn *, void *);
 extern int blk_rq_map_user(request_queue_t *, struct request *, void __user *, unsigned int);
 extern int blk_rq_unmap_user(struct bio *, unsigned int);