block: fixup block IO unplug trace call

It was removed with the on-stack plugging, readd it and track the
depth of requests added when flushing the plug.
Signed-off-by: Jens Axboe <jaxboe@fusionio.com>

block/blk-core.c

@@ -2668,12 +2668,19 @@ static int plug_rq_cmp(void *priv, struct list_head *a, struct list_head *b)
 	return !(rqa->q <= rqb->q);
 }
 
+static void queue_unplugged(struct request_queue *q, unsigned int depth)
+{
+	trace_block_unplug_io(q, depth);
+	__blk_run_queue(q, false);
+}
+
 static void flush_plug_list(struct blk_plug *plug)
 {
 	struct request_queue *q;
 	unsigned long flags;
 	struct request *rq;
 	LIST_HEAD(list);
+	unsigned int depth;
 
 	BUG_ON(plug->magic != PLUG_MAGIC);
 
@@ -2688,6 +2695,7 @@ static void flush_plug_list(struct blk_plug *plug)
 	}
 
 	q = NULL;
+	depth = 0;
 	local_irq_save(flags);
 	while (!list_empty(&list)) {
 		rq = list_entry_rq(list.next);
@@ -2696,10 +2704,11 @@ static void flush_plug_list(struct blk_plug *plug)
 		BUG_ON(!rq->q);
 		if (rq->q != q) {
 			if (q) {
-				__blk_run_queue(q, false);
+				queue_unplugged(q, depth);
 				spin_unlock(q->queue_lock);
 			}
 			q = rq->q;
+			depth = 0;
 			spin_lock(q->queue_lock);
 		}
 		rq->cmd_flags &= ~REQ_ON_PLUG;
@@ -2711,10 +2720,12 @@ static void flush_plug_list(struct blk_plug *plug)
 			__elv_add_request(q, rq, ELEVATOR_INSERT_FLUSH);
 		else
 			__elv_add_request(q, rq, ELEVATOR_INSERT_SORT_MERGE);
+
+		depth++;
 	}
 
 	if (q) {
-		__blk_run_queue(q, false);
+		queue_unplugged(q, depth);
 		spin_unlock(q->queue_lock);
 	}
 

include/trace/events/block.h

@@ -401,9 +401,9 @@ TRACE_EVENT(block_plug,
 
 DECLARE_EVENT_CLASS(block_unplug,
 
-	TP_PROTO(struct request_queue *q),
+	TP_PROTO(struct request_queue *q, unsigned int depth),
 
-	TP_ARGS(q),
+	TP_ARGS(q, depth),
 
 	TP_STRUCT__entry(
 		__field( int,		nr_rq			)
@@ -411,7 +411,7 @@ DECLARE_EVENT_CLASS(block_unplug,
 	),
 
 	TP_fast_assign(
-		__entry->nr_rq	= q->rq.count[READ] + q->rq.count[WRITE];
+		__entry->nr_rq = depth;
 		memcpy(__entry->comm, current->comm, TASK_COMM_LEN);
 	),
 
@@ -421,15 +421,16 @@ DECLARE_EVENT_CLASS(block_unplug,
 /**
  * block_unplug_io - release of operations requests in request queue
  * @q: request queue to unplug
+ * @depth: number of requests just added to the queue
  *
  * Unplug request queue @q because device driver is scheduled to work
  * on elements in the request queue.
  */
 DEFINE_EVENT(block_unplug, block_unplug_io,
 
-	TP_PROTO(struct request_queue *q),
+	TP_PROTO(struct request_queue *q, unsigned int depth),
 
-	TP_ARGS(q)
+	TP_ARGS(q, depth)
 );
 
 /**

kernel/trace/blktrace.c

@@ -850,13 +850,13 @@ static void blk_add_trace_plug(void *ignore, struct request_queue *q)
 		__blk_add_trace(bt, 0, 0, 0, BLK_TA_PLUG, 0, 0, NULL);
 }
 
-static void blk_add_trace_unplug_io(void *ignore, struct request_queue *q)
+static void blk_add_trace_unplug_io(void *ignore, struct request_queue *q,
+				    unsigned int depth)
 {
 	struct blk_trace *bt = q->blk_trace;
 
 	if (bt) {
-		unsigned int pdu = q->rq.count[READ] + q->rq.count[WRITE];
-		__be64 rpdu = cpu_to_be64(pdu);
+		__be64 rpdu = cpu_to_be64(depth);
 
 		__blk_add_trace(bt, 0, 0, 0, BLK_TA_UNPLUG_IO, 0,
 				sizeof(rpdu), &rpdu);