netdev - Re: [PATCH net 1/2] tcp: fix tcp_cong_avoid_ai() credit accumulation bug with decreases in w

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Message-Id: <20150311.165208.101538124570318344.davem@davemloft.net>
Date:	Wed, 11 Mar 2015 16:52:08 -0400 (EDT)
From:	David Miller <davem@...emloft.net>
To:	ncardwell@...gle.com
Cc:	netdev@...r.kernel.org, ycheng@...gle.com, edumazet@...gle.com
Subject: Re: [PATCH net 1/2] tcp: fix tcp_cong_avoid_ai() credit
 accumulation bug with decreases in w

From: Neal Cardwell <ncardwell@...gle.com>
Date: Tue, 10 Mar 2015 17:17:03 -0400

> The recent change to tcp_cong_avoid_ai() to handle stretch ACKs
> introduced a bug where snd_cwnd_cnt could accumulate a very large
> value while w was large, and then if w was reduced snd_cwnd could be
> incremented by a large delta, leading to a large burst and high packet
> loss. This was tickled when CUBIC's bictcp_update() sets "ca->cnt =
> 100 * cwnd".
> 
> This bug crept in while preparing the upstream version of
> 814d488c6126.
> 
> Testing: This patch has been tested in datacenter netperf transfers
> and live youtube.com and google.com servers.
> 
> Fixes: 814d488c6126 ("tcp: fix the timid additive increase on stretch ACKs")
> Signed-off-by: Neal Cardwell <ncardwell@...gle.com>
> Signed-off-by: Yuchung Cheng <ycheng@...gle.com>
> Signed-off-by: Eric Dumazet <edumazet@...gle.com>

Applied.
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