--- zzzz-none-000/linux-3.10.107/net/sched/sch_fifo.c	2017-06-27 09:49:32.000000000 +0000
+++ scorpion-7490-727/linux-3.10.107/net/sched/sch_fifo.c	2021-02-04 17:41:59.000000000 +0000
@@ -37,14 +37,18 @@
 
 static int pfifo_tail_enqueue(struct sk_buff *skb, struct Qdisc *sch)
 {
+	unsigned int prev_backlog;
+
 	if (likely(skb_queue_len(&sch->q) < sch->limit))
 		return qdisc_enqueue_tail(skb, sch);
 
+	prev_backlog = sch->qstats.backlog;
 	/* queue full, remove one skb to fulfill the limit */
 	__qdisc_queue_drop_head(sch, &sch->q);
-	sch->qstats.drops++;
+	qdisc_qstats_drop(sch);
 	qdisc_enqueue_tail(skb, sch);
 
+	qdisc_tree_reduce_backlog(sch, 0, prev_backlog - sch->qstats.backlog);
 	return NET_XMIT_CN;
 }
 
@@ -54,7 +58,7 @@
 	bool is_bfifo = sch->ops == &bfifo_qdisc_ops;
 
 	if (opt == NULL) {
-		u32 limit = qdisc_dev(sch)->tx_queue_len ? : 1;
+		u32 limit = qdisc_dev(sch)->tx_queue_len;
 
 		if (is_bfifo)
 			limit *= psched_mtu(qdisc_dev(sch));