netdev - Re: [Patch net-next v2 2/4] net_sched: update hierarchical backlog too

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Message-ID: <CAHA+R7NkU3Bme5MbgFraOo=7SRYUF+F-6owyzFxfVidjc2AxMw@mail.gmail.com>
Date:	Mon, 2 Nov 2015 13:09:30 -0800
From:	Cong Wang <cwang@...pensource.com>
To:	Eric Dumazet <eric.dumazet@...il.com>
Cc:	Cong Wang <xiyou.wangcong@...il.com>,
	netdev <netdev@...r.kernel.org>,
	Jamal Hadi Salim <jhs@...atatu.com>
Subject: Re: [Patch net-next v2 2/4] net_sched: update hierarchical backlog too

(Sorry for the delay)

On Fri, Oct 30, 2015 at 12:30 PM, Eric Dumazet <eric.dumazet@...il.com> wrote:
> On Fri, 2015-10-30 at 11:22 -0700, Cong Wang wrote:
>> 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)

Are you saying some qdisc_tree_reduce_backlog() is missing? It could be,
since I don't audit that, if so, I'd do that in a separated patch, because this
patch is supposed to fix existing qdisc_tree_reduce_backlog().

Does this make sense for you?

Thanks.
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