Print clue to reduce queue depth if engine init fails

Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
diff --git a/ioengines.c b/ioengines.c
index 0e5ea62..4ab08ce 100644
--- a/ioengines.c
+++ b/ioengines.c
@@ -238,10 +238,15 @@
 
 int td_io_init(struct thread_data *td)
 {
-	if (td->io_ops->init)
-		return td->io_ops->init(td);
+	int ret = 0;
 
-	return 0;
+	if (td->io_ops->init) {
+		ret = td->io_ops->init(td);
+		if (ret && td->o.iodepth > 1)
+			log_err("fio: io engine init failed. Perhaps try reducing io dpeth?\n");
+	}
+
+	return ret;
 }
 
 int td_io_commit(struct thread_data *td)