On Fri, 2015-10-30 at 11:22 -0700, Cong Wang wrote:
> When the bottom qdisc decides to, for example, drop some packet,
> it calls qdisc_tree_decrease_qlen() to update the queue length
> for all its ancestors, we need to update the backlog too to
> keep the stats on root qdisc accurate.
>
> Cc: Jamal Hadi Salim <j...@mojatatu.com>
> Acked-by: Jamal Hadi Salim <j...@mojatatu.com>
> Signed-off-by: Cong Wang <xiyou.wangc...@gmail.com>
...
>
> diff --git a/net/sched/sch_sfq.c b/net/sched/sch_sfq.c
> index 3abab53..498f0a2 100644
> --- a/net/sched/sch_sfq.c
> +++ b/net/sched/sch_sfq.c
> @@ -346,7 +346,7 @@ static int
> sfq_enqueue(struct sk_buff *skb, struct Qdisc *sch)
> {
> struct sfq_sched_data *q = qdisc_priv(sch);
> - unsigned int hash;
> + unsigned int hash, dropped;
> sfq_index x, qlen;
> struct sfq_slot *slot;
> int uninitialized_var(ret);
> @@ -461,7 +461,7 @@ sfq_enqueue(struct sk_buff *skb, struct Qdisc *sch)
> return NET_XMIT_SUCCESS;
>
> qlen = slot->qlen;
> - sfq_drop(sch);
> + dropped = sfq_drop(sch);
> /* Return Congestion Notification only if we dropped a packet
> * from this flow.
> */
> @@ -469,7 +469,7 @@ sfq_enqueue(struct sk_buff *skb, struct Qdisc *sch)
> return NET_XMIT_CN;
I believe you missed the NET_XMIT_CN cases.
SFQ can drop a prior packet, and queue current packet.
qdisc_tree_reduce_backlog() wont be called to update parents.
Not sure about other qdisc(s)
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