netdev - Re: [PATCH v2] tcp: detect loss above high

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Date:	Sun, 22 Jan 2012 14:24:16 -0500 (EST)
From:	David Miller <davem@...emloft.net>
To:	ycheng@...gle.com
Cc:	ilpo.jarvinen@...sinki.fi, ncardwell@...gle.com,
	nanditad@...gle.com, netdev@...r.kernel.org
Subject: Re: [PATCH v2] tcp: detect loss above high_seq in recovery

From: Yuchung Cheng <ycheng@...gle.com>
Date: Thu, 19 Jan 2012 16:42:21 -0800

> Correctly implement a loss detection heuristic: New sequences (above
> high_seq) sent during the fast recovery are deemed lost when higher
> sequences are SACKed.
> 
> Current code does not catch these losses, because tcp_mark_head_lost()
> does not check packets beyond high_seq. The fix is straight-forward by
> checking packets until the highest sacked packet. In addition, all the
> FLAG_DATA_LOST logic are in-effective and redundant and can be removed.
> 
> Update the loss heuristic comments. The algorithm above is documented
> as heuristic B, but it is redundant too because heuristic A already
> covers B.
> 
> Note that this change only marks some forward-retransmitted packets LOST.
> It does NOT forbid TCP performing further CWR on new losses. A potential
> follow-up patch under preparation is to perform another CWR on "new"
> losses such as
> 1) sequence above high_seq is lost (by resetting high_seq to snd_nxt)
> 2) retransmission is lost.
> 
> Signed-off-by: Yuchung Cheng <ycheng@...gle.com>

Applied.
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