block: avoid unnecessary plug list flush

get_request_wait() could sleep and flush the plug list. If the list is already flushed, don't flush again. Signed-off-by: Shaohua Li <[email protected]> Reviewed-by: Namhyung Kim <[email protected]> Signed-off-by: Andrew Morton <[email protected]> Signed-off-by: Jens Axboe <[email protected]>
goeke · Nov 16, 2011 · 3540d5e · 3540d5e
1 parent 0007a4c
commit 3540d5e
Showing 1 changed file with 9 additions and 7 deletions.
diff --git a/block/blk-core.c b/block/blk-core.c
@@ -1379,15 +1379,17 @@ void blk_queue_bio(struct request_queue *q, struct bio *bio)
 		 */
 		if (list_empty(&plug->list))
 			trace_block_plug(q);
-		else if (!plug->should_sort) {
-			struct request *__rq;
+		else {
+			if (!plug->should_sort) {
+				struct request *__rq;
 
-			__rq = list_entry_rq(plug->list.prev);
-			if (__rq->q != q)
-				plug->should_sort = 1;
+				__rq = list_entry_rq(plug->list.prev);
+				if (__rq->q != q)
+					plug->should_sort = 1;
+			}
+			if (request_count >= BLK_MAX_REQUEST_COUNT)
+				blk_flush_plug_list(plug, false);
 		}
-		if (request_count >= BLK_MAX_REQUEST_COUNT)
-			blk_flush_plug_list(plug, false);
 		list_add_tail(&req->queuelist, &plug->list);
 		drive_stat_acct(req, 1);
 	} else {