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Commit 80e509db authored by Eric Dumazet's avatar Eric Dumazet Committed by David S. Miller
Browse files

fq_codel: fix NET_XMIT_CN behavior 



My prior attempt to fix the backlogs of parents failed.

If we return NET_XMIT_CN, our parents wont increase their backlog,
so our qdisc_tree_reduce_backlog() should take this into account.

v2: Florian Westphal pointed out that we could drop the packet,
so we need to save qdisc_pkt_len(skb) in a temp variable before
calling fq_codel_drop()

Fixes: 9d18562a ("fq_codel: add batch ability to fq_codel_drop()")
Fixes: 2ccccf5f ("net_sched: update hierarchical backlog too")
Reported-by: default avatarStas Nichiporovich <stasn77@gmail.com>
Signed-off-by: default avatarEric Dumazet <edumazet@google.com>
Cc: WANG Cong <xiyou.wangcong@gmail.com>
Cc: Jamal Hadi Salim <jhs@mojatatu.com>
Acked-by: default avatarJamal Hadi Salim <jhs@mojatatu.com>
Acked-by: default avatarCong Wang <xiyou.wangcong@gmail.com>
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
parent 5b6c1b4d

net/sched/sch_fq_codel.c

+18 −6
Original line number Diff line number Diff line
@@ -199,6 +199,7 @@ static int fq_codel_enqueue(struct sk_buff *skb, struct Qdisc *sch) 
	unsigned int idx, prev_backlog, prev_qlen;

	struct fq_codel_flow *flow;

	int uninitialized_var(ret);

	unsigned int pkt_len;

	bool memory_limited;



	idx = fq_codel_classify(skb, sch, &ret);
@@ -230,6 +231,8 @@ static int fq_codel_enqueue(struct sk_buff *skb, struct Qdisc *sch) 
	prev_backlog = sch->qstats.backlog;

	prev_qlen = sch->q.qlen;



	/* save this packet length as it might be dropped by fq_codel_drop() */

	pkt_len = qdisc_pkt_len(skb);

	/* fq_codel_drop() is quite expensive, as it performs a linear search

	 * in q->backlogs[] to find a fat flow.

	 * So instead of dropping a single packet, drop half of its backlog
@@ -237,14 +240,23 @@ static int fq_codel_enqueue(struct sk_buff *skb, struct Qdisc *sch) 
	 */

	ret = fq_codel_drop(sch, q->drop_batch_size);



	q->drop_overlimit += prev_qlen - sch->q.qlen;

	prev_qlen -= sch->q.qlen;

	prev_backlog -= sch->qstats.backlog;

	q->drop_overlimit += prev_qlen;

	if (memory_limited)

		q->drop_overmemory += prev_qlen - sch->q.qlen;

	/* As we dropped packet(s), better let upper stack know this */

	qdisc_tree_reduce_backlog(sch, prev_qlen - sch->q.qlen,

				  prev_backlog - sch->qstats.backlog);

		q->drop_overmemory += prev_qlen;



	return ret == idx ? NET_XMIT_CN : NET_XMIT_SUCCESS;

	/* As we dropped packet(s), better let upper stack know this.

	 * If we dropped a packet for this flow, return NET_XMIT_CN,

	 * but in this case, our parents wont increase their backlogs.

	 */

	if (ret == idx) {

		qdisc_tree_reduce_backlog(sch, prev_qlen - 1,

					  prev_backlog - pkt_len);

		return NET_XMIT_CN;

	}

	qdisc_tree_reduce_backlog(sch, prev_qlen, prev_backlog);

	return NET_XMIT_SUCCESS;

}



/* This is the specific function called from codel_dequeue()