netdev - Re: [PATCH v2 net] fq_codel: fix NET_XMIT

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Date:	Mon, 6 Jun 2016 06:49:26 -0400
From:	Jamal Hadi Salim <jhs@...atatu.com>
To:	Cong Wang <xiyou.wangcong@...il.com>,
	Eric Dumazet <eric.dumazet@...il.com>
Cc:	Florian Westphal <fw@...len.de>,
	David Miller <davem@...emloft.net>,
	netdev <netdev@...r.kernel.org>,
	Stas Nichiporovich <stasn77@...il.com>
Subject: Re: [PATCH v2 net] fq_codel: fix NET_XMIT_CN behavior

On 16-06-05 07:30 PM, Cong Wang wrote:

> Potentially all of the following:
>
> net/sched/sch_choke.c:  return NET_XMIT_CN;
> net/sched/sch_fifo.c:   return NET_XMIT_CN;
> net/sched/sch_generic.c:        return NET_XMIT_CN;
> net/sched/sch_gred.c:   return NET_XMIT_CN;
> net/sched/sch_hhf.c:            return NET_XMIT_CN;
> net/sched/sch_red.c:    return NET_XMIT_CN;
> net/sched/sch_sfb.c:    return NET_XMIT_CN;
> net/sched/sch_sfq.c:            return NET_XMIT_CN;
>

As long as we are not loosing the stat that the packet
is dropped. Some qdiscs have a counter which indicates
congestion drops(look at RED variants of early drops);
maybe codel needs one. The parent also must account for
childs drops.
BTW, returning NET_XMIT_CN could be confusing to tcp;
it does not mean that the packet that we are getting return
code for was dropped; it could mean _another_ packet in
the queue was dropped.

cheers,
jamal