netdev - Re: [PATCH] tcp: ECN blackhole should not force quickack mode

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Message-Id: <20110923.134734.2267391217120737650.davem@davemloft.net>
Date:	Fri, 23 Sep 2011 13:47:34 -0400 (EDT)
From:	David Miller <davem@...emloft.net>
To:	eric.dumazet@...il.com
Cc:	netdev@...r.kernel.org, hkchu@...gle.com,
	ilpo.jarvinen@...sinki.fi, jhs@...atatu.com, jg@...edesktop.org,
	dave.taht@...il.com
Subject: Re: [PATCH] tcp: ECN blackhole should not force quickack mode

From: Eric Dumazet <eric.dumazet@...il.com>
Date: Fri, 23 Sep 2011 08:02:19 +0200

> While playing with a new ADSL box at home, I discovered that ECN
> blackhole can trigger suboptimal quickack mode on linux : We send one
> ACK for each incoming data frame, without any delay and eventual
> piggyback.
> 
> This is because TCP_ECN_check_ce() considers that if no ECT is seen on a
> segment, this is because this segment was a retransmit.
> 
> Refine this heuristic and apply it only if we seen ECT in a previous
> segment, to detect ECN blackhole at IP level.
> 
> Signed-off-by: Eric Dumazet <eric.dumazet@...il.com>
> CC: Jamal Hadi Salim <jhs@...atatu.com>
> CC: Jerry Chu <hkchu@...gle.com>
> CC: Ilpo Järvinen <ilpo.jarvinen@...sinki.fi>
> CC: Jim Gettys <jg@...edesktop.org>
> CC: Dave Taht <dave.taht@...il.com>
> ---
> Another possibility is to remove this (not in RFC 3168) heuristic, what
> do you think ?

Jamal, please give this a look over.  Thanks!
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