netdev - Re: [PATCH net-next] tcp: tcp_transmit

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Message-Id: <20131011.174858.1461090000704613432.davem@davemloft.net>
Date:	Fri, 11 Oct 2013 17:48:58 -0400 (EDT)
From:	David Miller <davem@...emloft.net>
To:	eric.dumazet@...il.com
Cc:	netdev@...r.kernel.org, fitz@...yale.edu, ycheng@...gle.com,
	ncardwell@...gle.com
Subject: Re: [PATCH net-next] tcp: tcp_transmit_skb() optimizations

From: Eric Dumazet <eric.dumazet@...il.com>
Date: Thu, 10 Oct 2013 08:43:00 -0700

> From: Eric Dumazet <edumazet@...gle.com>
> 
> 1) We need to take a timestamp only for skb that should be cloned.
> 
> Other skbs are not in write queue and no rtt estimation is done on them.
> 
> 2) the unlikely() hint is wrong for receivers (they send pure ACK)
> 
> Signed-off-by: Eric Dumazet <edumazet@...gle.com>

This patch is correct, so I've applied it, but it points out a bug.

The __tcp_retransmit_skb() code that does a __pskb_copy() to handle
NET_IP_ALIGN violations and skb_headroom() overflows is buggy because
it needs to store a congestion control timestamp in the original 'skb'
since that's what we'll look at in the retransmit queue.
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