netdev - Re: [PATCH 2/2 net-next] tcp: sk_add_backlog() is too agressive for TCP

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Message-Id: <20120424.044837.771495850418417499.davem@davemloft.net>
Date:	Tue, 24 Apr 2012 04:48:37 -0400 (EDT)
From:	David Miller <davem@...emloft.net>
To:	ilpo.jarvinen@...sinki.fi
Cc:	eric.dumazet@...il.com, rick.jones2@...com, netdev@...r.kernel.org,
	therbert@...gle.com, ncardwell@...gle.com, maze@...gle.com,
	ycheng@...gle.com
Subject: Re: [PATCH 2/2 net-next] tcp: sk_add_backlog() is too agressive
 for TCP

From: "Ilpo Järvinen" <ilpo.jarvinen@...sinki.fi>
Date: Tue, 24 Apr 2012 11:40:27 +0300 (EEST)

> And the problem I mentioned in the previous mail (in the terms of this 
> code fragment) is that ackdiff is no longer MSS or 2*MSS because of GRO 
> for the opposite direction doesn't trigger all those ACKs a non-GRO 
> receiver would.

This is the ACK counting Eric mentioned, which we need to preserve
for the purposes of CWND growth.

And in any event, you cannot depend upon the ACK boundaries in any way
shape or form, 2 * MSS is just one valid mode of ACK'ing.

Whether we get a GRO stretch ACK or a normal 2 * MSS one, it has to
work properly either way.
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