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

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Message-ID: <561E4663.4080101@mojatatu.com>
Date:	Wed, 14 Oct 2015 08:11:15 -0400
From:	Jamal Hadi Salim <jhs@...atatu.com>
To:	Cong Wang <xiyou.wangcong@...il.com>, netdev@...r.kernel.org
Subject: Re: [Patch net-next 2/4] net_sched: update hierarchical backlog too

On 10/12/15 14:38, 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.
>

There is more than one change in there (the codel change seems
out of place and i wasnt sure why it was needed).
Also it seems possible you are double-dipping in some cases;
i dont have time to scrutinize - but looking at codel_change() change
when the queue limit is exceeded you will end up affecting backlog from
both qdisc_qstats_backlog_dec() and your new
qdisc_tree_reduce_backlog()

BTW: Codel usage of looking at queue limit during control update
seems strange.

cheers,
jamal
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