netdev - Re: [PATCH] tcp: tsq: fix nonagle handling

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Date:	Mon, 10 Feb 2014 15:24:16 -0800 (PST)
From:	David Miller <davem@...emloft.net>
To:	eric.dumazet@...il.com
Cc:	netdev@...r.kernel.org, john.ogness@...utronix.de,
	thomas@...nzmann.de
Subject: Re: [PATCH] tcp: tsq: fix nonagle handling

From: Eric Dumazet <eric.dumazet@...il.com>
Date: Sun, 09 Feb 2014 18:40:11 -0800

> From: John Ogness <john.ogness@...utronix.de>
> 
> Commit 46d3ceabd8d9 ("tcp: TCP Small Queues") introduced a possible
> regression for applications using TCP_NODELAY.
> 
> If TCP session is throttled because of tsq, we should consult
> tp->nonagle when TX completion is done and allow us to send additional
> segment, especially if this segment is not a full MSS.
> Otherwise this segment is sent after an RTO.
> 
> [edumazet] : Cooked the changelog, added another fix about testing
> sk_wmem_alloc twice because TX completion can happen right before
> setting TSQ_THROTTLED bit.
> 
> This problem is particularly visible with recent auto corking,
> but might also be triggered with low tcp_limit_output_bytes
> values or NIC drivers delaying TX completion by hundred of usec,
> and very low rtt.
> 
> Thomas Glanzmann for example reported an iscsi regression, caused
> by tcp auto corking making this bug quite visible.
> 
> Fixes: 46d3ceabd8d9 ("tcp: TCP Small Queues")
> Signed-off-by: John Ogness <john.ogness@...utronix.de>
> Signed-off-by: Eric Dumazet <edumazet@...gle.com>
> Reported-by: Thomas Glanzmann <thomas@...nzmann.de>

Applied and queued up for -stable, thanks!
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