netdev - Re: [PATCH net-next] tcp: ecn: dont delay ACKS after CE

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Date:	Mon, 06 Aug 2012 14:14:51 -0700 (PDT)
From:	David Miller <davem@...emloft.net>
To:	ncardwell@...gle.com
Cc:	eric.dumazet@...il.com, netdev@...r.kernel.org
Subject: Re: [PATCH net-next] tcp: ecn: dont delay ACKS after CE

From: Neal Cardwell <ncardwell@...gle.com>
Date: Mon, 6 Aug 2012 17:07:08 -0400

> On Mon, Aug 6, 2012 at 5:04 PM, Eric Dumazet <eric.dumazet@...il.com> wrote:
>> From: Eric Dumazet <edumazet@...gle.com>
>>
>> While playing with CoDel and ECN marking, I discovered a
>> non optimal behavior of receiver of CE (Congestion Encountered)
>> segments.
>>
>> In pathological cases, sender has reduced its cwnd to low values,
>> and receiver delays its ACK (by 40 ms).
>>
>> While RFC 3168 6.1.3 (The TCP Receiver) doesn't explicitly recommend
>> to send immediate ACKS, we believe its better to not delay ACKS, because
>> a CE segment should give same signal than a dropped segment, and its
>> quite important to reduce RTT to give ECE/CWR signals as fast as
>> possible.
>>
>> Note we already call tcp_enter_quickack_mode() from TCP_ECN_check_ce()
>> if we receive a retransmit, for the same reason.
>>
>> Signed-off-by: Eric Dumazet <edumazet@...gle.com>
>> Cc: Neal Cardwell <ncardwell@...gle.com>
> 
> Acked-by: Neal Cardwell <ncardwell@...gle.com>

Applied, thanks.
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