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

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Date:	Mon, 6 Jun 2016 13:42:34 +0200
From:	Florian Westphal <fw@...len.de>
To:	Jamal Hadi Salim <jhs@...atatu.com>
Cc:	Cong Wang <xiyou.wangcong@...il.com>,
	Eric Dumazet <eric.dumazet@...il.com>,
	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

Jamal Hadi Salim <jhs@...atatu.com> wrote:
> 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.

Yes, but we currently conceal NET_XMIT_CN from upper layer (tcp)
via the net_xmit_* macros:

#define net_xmit_eval(e)       ((e) == NET_XMIT_CN ? 0 : (e))
#define net_xmit_errno(e)      ((e) != NET_XMIT_CN ? -ENOBUFS : 0)

Might be worth changing this so tcp reduces cwnd in _CN case too.