netdev - Re: [PATCH 4/4 net-next] tcp: makes tcp_try_coalesce aware of skb->head

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Date:	Mon, 30 Apr 2012 21:48:47 -0400 (EDT)
From:	David Miller <davem@...emloft.net>
To:	eric.dumazet@...il.com
Cc:	netdev@...r.kernel.org, ncardwell@...gle.com,
	jeffrey.t.kirsher@...el.com, therbert@...gle.com,
	herbert@...dor.hengli.com.au, bhutchings@...arflare.com,
	mcarlson@...adcom.com, mchan@...adcom.com, maze@...gle.com,
	ilpo.jarvinen@...sinki.fi
Subject: Re: [PATCH 4/4 net-next] tcp: makes tcp_try_coalesce aware of
 skb->head_frag

From: Eric Dumazet <eric.dumazet@...il.com>
Date: Fri, 27 Apr 2012 12:38:33 +0200

> From: Eric Dumazet <edumazet@...gle.com>
> 
> TCP coalesce can check if skb to be merged has its skb->head mapped to a
> page fragment, instead of a kmalloc() area.
> 
> We had to disable coalescing in this case, for performance reasons.
> 
> We 'upgrade' skb->head as a fragment in itself.
> 
> This reduces number of cache misses when user makes its copies, since a
> less sk_buff are fetched.
> 
> This makes receive and ofo queues shorter and thus reduce cache line
> misses in TCP stack.
> 
> This is a followup of patch "net: allow skb->head to be a page fragment"
> 
> Tested with tg3 nic, with GRO on or off. We can see "TCPRcvCoalesce"
> counter being incremented.
> 
> Signed-off-by: Eric Dumazet <edumazet@...gle.com>

Applied.
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