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@@ -0,0 +1,70 @@
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+From: Eric Dumazet <[email protected]>
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+Date: Sat, 4 Jun 2016 12:55:13 -0700
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+Subject: [PATCH] fq_codel: fix NET_XMIT_CN behavior
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+
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+My prior attempt to fix the backlogs of parents failed.
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+
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+If we return NET_XMIT_CN, our parents wont increase their backlog,
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+so our qdisc_tree_reduce_backlog() should take this into account.
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+
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+v2: Florian Westphal pointed out that we could drop the packet,
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+so we need to save qdisc_pkt_len(skb) in a temp variable before
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+calling fq_codel_drop()
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+
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+Fixes: 9d18562a2278 ("fq_codel: add batch ability to fq_codel_drop()")
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+Fixes: 2ccccf5fb43f ("net_sched: update hierarchical backlog too")
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+Reported-by: Stas Nichiporovich <[email protected]>
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+Signed-off-by: Eric Dumazet <[email protected]>
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+Cc: WANG Cong <[email protected]>
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+Cc: Jamal Hadi Salim <[email protected]>
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+---
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+
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+--- a/net/sched/sch_fq_codel.c
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++++ b/net/sched/sch_fq_codel.c
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+@@ -197,6 +197,7 @@ static int fq_codel_enqueue(struct sk_bu
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+ unsigned int idx, prev_backlog, prev_qlen;
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+ struct fq_codel_flow *flow;
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+ int uninitialized_var(ret);
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++ unsigned int pkt_len;
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+ bool memory_limited;
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+
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+ idx = fq_codel_classify(skb, sch, &ret);
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+@@ -228,6 +229,8 @@ static int fq_codel_enqueue(struct sk_bu
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+ prev_backlog = sch->qstats.backlog;
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+ prev_qlen = sch->q.qlen;
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+
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++ /* save this packet length as it might be dropped by fq_codel_drop() */
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++ pkt_len = qdisc_pkt_len(skb);
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+ /* fq_codel_drop() is quite expensive, as it performs a linear search
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+ * in q->backlogs[] to find a fat flow.
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+ * So instead of dropping a single packet, drop half of its backlog
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+@@ -235,14 +238,23 @@ static int fq_codel_enqueue(struct sk_bu
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+ */
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+ ret = fq_codel_drop(sch, q->drop_batch_size);
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+
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+- q->drop_overlimit += prev_qlen - sch->q.qlen;
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++ prev_qlen -= sch->q.qlen;
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++ prev_backlog -= sch->qstats.backlog;
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++ q->drop_overlimit += prev_qlen;
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+ if (memory_limited)
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+- q->drop_overmemory += prev_qlen - sch->q.qlen;
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+- /* As we dropped packet(s), better let upper stack know this */
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+- qdisc_tree_reduce_backlog(sch, prev_qlen - sch->q.qlen,
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+- prev_backlog - sch->qstats.backlog);
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++ q->drop_overmemory += prev_qlen;
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+
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+- return ret == idx ? NET_XMIT_CN : NET_XMIT_SUCCESS;
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++ /* As we dropped packet(s), better let upper stack know this.
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++ * If we dropped a packet for this flow, return NET_XMIT_CN,
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++ * but in this case, our parents wont increase their backlogs.
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++ */
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++ if (ret == idx) {
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++ qdisc_tree_reduce_backlog(sch, prev_qlen - 1,
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++ prev_backlog - pkt_len);
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++ return NET_XMIT_CN;
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++ }
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++ qdisc_tree_reduce_backlog(sch, prev_qlen, prev_backlog);
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++ return NET_XMIT_SUCCESS;
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+ }
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+
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+ /* This is the specific function called from codel_dequeue()
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Felix Fietkau