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

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Date:	Mon, 6 Jun 2016 18:18:43 +0200
From:	Florian Westphal <fw@...len.de>
To:	Eric Dumazet <eric.dumazet@...il.com>
Cc:	Florian Westphal <fw@...len.de>,
	Jamal Hadi Salim <jhs@...atatu.com>,
	Cong Wang <xiyou.wangcong@...il.com>,
	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

Eric Dumazet <eric.dumazet@...il.com> wrote:
> On Mon, 2016-06-06 at 13:42 +0200, Florian Westphal wrote:
> > 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.
> 
> It always had been the case.
> 
> tcp_transmit_skb() calls tcp_enter_cwr(), unless someone broke this.

No, you're right.  We hide error in ip_send_skb but that function is
not used in tcp case.

So all is good here.