netdev - Re: [PATCH net-next] tcp: reset reordering est. selectively on timeout

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Message-ID: <CADVnQykaYF5xQJbv-m6d3xKMHSYZQVjmua2CqXkGdwdo_iqSwA@mail.gmail.com>
Date:	Tue, 13 Aug 2013 00:16:57 -0400
From:	Neal Cardwell <ncardwell@...gle.com>
To:	Yuchung Cheng <ycheng@...gle.com>
Cc:	David Miller <davem@...emloft.net>,
	Eric Dumazet <edumazet@...gle.com>,
	Matt Mathis <mattmathis@...gle.com>,
	Netdev <netdev@...r.kernel.org>
Subject: Re: [PATCH net-next] tcp: reset reordering est. selectively on timeout

On Mon, Aug 12, 2013 at 7:41 PM, Yuchung Cheng <ycheng@...gle.com> wrote:
> On timeout the TCP sender unconditionally reset the estimated
> degree of network reordering (tp->reordering). This idea behind
> is that the estimate is too large to trigger fast recovery
> (e.g., due to a IP path change).
>
> But for example if the sender only had 2 packets outstanding,
> then a timeout doesn't tell much about reordering. A sender that
> learns about reordering on big writes and lose packets on small
> writes will end up falsely retransmit again and again, especially
> when reordering is more likely on big writes.
>
> Therefore the sender should only suspects tp->reordering is too
> high if it could have gone into fast recovery with the (lower)
> default estimate.
>
> Signed-off-by: Yuchung Cheng <ycheng@...gle.com>
> ---
>  net/ipv4/tcp_input.c | 9 +++++++--
>  1 file changed, 7 insertions(+), 2 deletions(-)

Acked-by: Neal Cardwell <ncardwell@...gle.com>

neal
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