block: readd plug trace event

This was removed with the queue plug state. But we can easily readd by checking if this is the first request going to this queue. It's good information to have when tracing to see how effective the plugging is. Signed-off-by: Jens Axboe <[email protected]>
koalo · Apr 12, 2011 · dc6d36c · dc6d36c
1 parent f756645
commit dc6d36c
Showing 1 changed file with 9 additions and 1 deletion.
diff --git a/block/blk-core.c b/block/blk-core.c
@@ -1311,7 +1311,15 @@ static int __make_request(struct request_queue *q, struct bio *bio)
 
 	plug = current->plug;
 	if (plug) {
-		if (!plug->should_sort && !list_empty(&plug->list)) {
+		/*
+		 * If this is the first request added after a plug, fire
+		 * of a plug trace. If others have been added before, check
+		 * if we have multiple devices in this plug. If so, make a
+		 * note to sort the list before dispatch.
+		 */
+		if (list_empty(&plug->list))
+			trace_block_plug(q);
+		else if (!plug->should_sort) {
 			struct request *__rq;
 
 			__rq = list_entry_rq(plug->list.prev);