target/linux/generic/patches-4.4/035-fq_codel-fix-NET_XMIT_CN-behavior.patch

   1 From: Eric Dumazet <edumazet@google.com>
   2 Date: Sat, 4 Jun 2016 12:55:13 -0700
   3 Subject: [PATCH] fq_codel: fix NET_XMIT_CN behavior
   4
   5 My prior attempt to fix the backlogs of parents failed.
   6
   7 If we return NET_XMIT_CN, our parents wont increase their backlog,
   8 so our qdisc_tree_reduce_backlog() should take this into account.
   9
  10 v2: Florian Westphal pointed out that we could drop the packet,
  11 so we need to save qdisc_pkt_len(skb) in a temp variable before
  12 calling fq_codel_drop()
  13
  14 Fixes: 9d18562a2278 ("fq_codel: add batch ability to fq_codel_drop()")
  15 Fixes: 2ccccf5fb43f ("net_sched: update hierarchical backlog too")
  16 Reported-by: Stas Nichiporovich <stasn77@gmail.com>
  17 Signed-off-by: Eric Dumazet <edumazet@google.com>
  18 Cc: WANG Cong <xiyou.wangcong@gmail.com>
  19 Cc: Jamal Hadi Salim <jhs@mojatatu.com>
  20 ---
  21
  22 --- a/net/sched/sch_fq_codel.c
  23 +++ b/net/sched/sch_fq_codel.c
  24 @@ -197,6 +197,7 @@ static int fq_codel_enqueue(struct sk_bu
  25         unsigned int idx, prev_backlog, prev_qlen;
  26         struct fq_codel_flow *flow;
  27         int uninitialized_var(ret);
  28 +       unsigned int pkt_len;
  29         bool memory_limited;
  30
  31         idx = fq_codel_classify(skb, sch, &ret);
  32 @@ -228,6 +229,8 @@ static int fq_codel_enqueue(struct sk_bu
  33         prev_backlog = sch->qstats.backlog;
  34         prev_qlen = sch->q.qlen;
  35
  36 +       /* save this packet length as it might be dropped by fq_codel_drop() */
  37 +       pkt_len = qdisc_pkt_len(skb);
  38         /* fq_codel_drop() is quite expensive, as it performs a linear search
  39          * in q->backlogs[] to find a fat flow.
  40          * So instead of dropping a single packet, drop half of its backlog
  41 @@ -235,14 +238,23 @@ static int fq_codel_enqueue(struct sk_bu
  42          */
  43         ret = fq_codel_drop(sch, q->drop_batch_size);
  44
  45 -       q->drop_overlimit += prev_qlen - sch->q.qlen;
  46 +       prev_qlen -= sch->q.qlen;
  47 +       prev_backlog -= sch->qstats.backlog;
  48 +       q->drop_overlimit += prev_qlen;
  49         if (memory_limited)
  50 -               q->drop_overmemory += prev_qlen - sch->q.qlen;
  51 -       /* As we dropped packet(s), better let upper stack know this */
  52 -       qdisc_tree_reduce_backlog(sch, prev_qlen - sch->q.qlen,
  53 -                                 prev_backlog - sch->qstats.backlog);
  54 +               q->drop_overmemory += prev_qlen;
  55
  56 -       return ret == idx ? NET_XMIT_CN : NET_XMIT_SUCCESS;
  57 +       /* As we dropped packet(s), better let upper stack know this.
  58 +        * If we dropped a packet for this flow, return NET_XMIT_CN,
  59 +        * but in this case, our parents wont increase their backlogs.
  60 +        */
  61 +       if (ret == idx) {
  62 +               qdisc_tree_reduce_backlog(sch, prev_qlen - 1,
  63 +                                         prev_backlog - pkt_len);
  64 +               return NET_XMIT_CN;
  65 +       }
  66 +       qdisc_tree_reduce_backlog(sch, prev_qlen, prev_backlog);
  67 +       return NET_XMIT_SUCCESS;
  68  }
  69
  70  /* This is the specific function called from codel_dequeue()