netdev - Re: [PATCH net-next v3] tcp: avoid reducing cwnd when ACK+DSACK is received

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Date:	Tue, 13 Jan 2015 14:22:35 -0500 (EST)
From:	David Miller <davem@...emloft.net>
To:	sebastien.barre@...ouvain.be
Cc:	ncardwell@...gle.com, ycheng@...gle.com, eric.dumazet@...il.com,
	netdev@...r.kernel.org, gregory.detal@...ouvain.be,
	nanditad@...gle.com
Subject: Re: [PATCH net-next v3] tcp: avoid reducing cwnd when ACK+DSACK is
 received

From: Sébastien Barré <sebastien.barre@...ouvain.be>
Date: Mon, 12 Jan 2015 10:30:40 +0100

> With TLP, the peer may reply to a probe with an
> ACK+D-SACK, with ack value set to tlp_high_seq. In the current code,
> such ACK+DSACK will be missed and only at next, higher ack will the TLP
> episode be considered done. Since the DSACK is not present anymore,
> this will cost a cwnd reduction.
> 
> This patch ensures that this scenario does not cause a cwnd reduction, since
> receiving an ACK+DSACK indicates that both the initial segment and the probe
> have been received by the peer.
> 
> The following packetdrill test, from Neal Cardwell, validates this patch:
 ...
> Credits:
> -Gregory helped in finding that tcp_process_tlp_ack was where the cwnd
> got reduced in our MPTCP tests.
> -Neal wrote the packetdrill test above
> -Yuchung reworked the patch to make it more readable.
> 
> Cc: Gregory Detal <gregory.detal@...ouvain.be>
> Cc: Nandita Dukkipati <nanditad@...gle.com>
> Tested-by: Neal Cardwell <ncardwell@...gle.com>
> Reviewed-by: Yuchung Cheng <ycheng@...gle.com>
> Reviewed-by: Eric Dumazet <eric.dumazet@...il.com>
> Signed-off-by: Sébastien Barré <sebastien.barre@...ouvain.be>

Applied, thanks everyone.
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