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

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Message-Id: <20130813.160851.329709982935426258.davem@davemloft.net>
Date:	Tue, 13 Aug 2013 16:08:51 -0700 (PDT)
From:	David Miller <davem@...emloft.net>
To:	ncardwell@...gle.com
Cc:	ycheng@...gle.com, edumazet@...gle.com, mattmathis@...gle.com,
	netdev@...r.kernel.org
Subject: Re: [PATCH net-next] tcp: reset reordering est. selectively on
 timeout

From: Neal Cardwell <ncardwell@...gle.com>
Date: Tue, 13 Aug 2013 00:16:57 -0400

> 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>

Applied, thanks.
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