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

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Message-ID: <CAHA+R7MogROyXLDhT7FrVLiLRhJueB0DmKGVDr49xDxcT2Q2KA@mail.gmail.com>
Date:	Mon, 2 Nov 2015 13:50:40 -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

On Mon, Nov 2, 2015 at 1:20 PM, Eric Dumazet <eric.dumazet@...il.com> wrote:
>
> Well, before your changes, the qdisc_tree_decrease_qlen(sch, 0) would
> have been useless, since qdisc_tree_decrease_qlen() does nothing in this
> case [1]
>
> But after your changes, we need to change the backlog, even if the qlen
> does not change.
>
> Maybe I missed something, but your patch is not really obvious ;)
>

Oh, very good point... You actually mean in some cases we enqueue
one packet and then drop one packet which ends up with dropping 0
packet but the backlog size goes down by (drop_len - enqueue_len). :)

Hmm, I need to double check for this case for sure, but for sfq case,
I just did:

-       qdisc_tree_decrease_qlen(sch, 1);
+       qdisc_tree_reduce_backlog(sch, 1, dropped);

which isn't the case where n==0, like you mentioned.

I am auditing that case for all the qdisc's anyway.

Thanks.
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