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

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Message-ID: <CADVnQyk25R4qpXq7Mho=uHwCswALPdOR=nP=AjQy7qJyT+HFuA@mail.gmail.com>
Date:	Mon, 6 Aug 2012 17:07:08 -0400
From:	Neal Cardwell <ncardwell@...gle.com>
To:	Eric Dumazet <eric.dumazet@...il.com>
Cc:	David Miller <davem@...emloft.net>, netdev <netdev@...r.kernel.org>
Subject: Re: [PATCH net-next] tcp: ecn: dont delay ACKS after CE

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>

neal
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