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- From: Eric Dumazet <[email protected]>
- Date: Sat, 4 Jun 2016 12:55:13 -0700
- Subject: [PATCH] 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: 9d18562a2278 ("fq_codel: add batch ability to fq_codel_drop()")
- Fixes: 2ccccf5fb43f ("net_sched: update hierarchical backlog too")
- Reported-by: Stas Nichiporovich <[email protected]>
- Signed-off-by: Eric Dumazet <[email protected]>
- Cc: WANG Cong <[email protected]>
- Cc: Jamal Hadi Salim <[email protected]>
- ---
- --- a/net/sched/sch_fq_codel.c
- +++ b/net/sched/sch_fq_codel.c
- @@ -197,6 +197,7 @@ static int fq_codel_enqueue(struct sk_bu
- 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);
- @@ -228,6 +229,8 @@ static int fq_codel_enqueue(struct sk_bu
- 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
- @@ -235,14 +238,23 @@ static int fq_codel_enqueue(struct sk_bu
- */
- 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()
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