Signed-off-by: Felix Fietkau <nbd@nbd.name>master
Felix Fietkau
8 years ago
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From: Eric Dumazet <edumazet@google.com>
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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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My prior attempt to fix the backlogs of parents failed.
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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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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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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 <stasn77@gmail.com>
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Signed-off-by: Eric Dumazet <edumazet@google.com>
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Cc: WANG Cong <xiyou.wangcong@gmail.com>
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Cc: Jamal Hadi Salim <jhs@mojatatu.com>
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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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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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+ /* 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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- 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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- 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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/* This is the specific function called from codel_dequeue()
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