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

From: Eric Dumazet <redacted>
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 <redacted>
CC: Jamal Hadi Salim <jhs@mojatatu.com>
CC: Jerry Chu <redacted>
CC: Ilpo Järvinen <redacted>
CC: Jim Gettys <redacted>
CC: Dave Taht <redacted>
---
Another possibility is to remove this (not in RFC 3168) heuristic, what
do you think ?

Jamal, please give this a look over.  Thanks!