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Date: Mon, 6 Nov 2006 14:57:57 -0800
From: Andrew Morton <akpm@osdl.org>
To: David Miller <davem@davemloft.net>
Cc: linux-kernel@vger.kernel.org, acme@conectiva.com.br
Subject: Re: + net-uninline-skb_put.patch added to -mm tree
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On Mon, 06 Nov 2006 14:42:33 -0800 (PST)
David Miller <davem@davemloft.net> wrote:

> From: akpm@osdl.org
> Date: Fri, 03 Nov 2006 14:18:29 -0800
> 
> > Subject: net: uninline skb_put()
> > From: Andrew Morton <akpm@osdl.org>
> > 
> > It has 34 callsites for a total of 2650 bytes.
> > 
> > Cc: Arnaldo Carvalho de Melo <acme@conectiva.com.br>
> > Signed-off-by: Andrew Morton <akpm@osdl.org>
> 
> A more accurate figure would probably be:
> 
> davem@sunset:~/src/GIT/net-2.6$ git grep skb_put | grep -v __skb_put | wc -l
> 1167
> 
> :-)

True.  I'm not sure what .config Arnaldo was using..

> Half of the cost of this interface are the assertions, which while
> useful are obviously over the top for such an oft-used routine in
> packet processing.
> 
> Without the assertion checks it's merely:
> 
> 	unsigned char *tmp = skb->tail;
> 	skb->tail += len;
> 	skb->len  += len;
> 	return tmp;
> 
> And even with 1167 call sites that is definitely something which
> should be inlined.

Yes.

Tricky.  I guess one suitable approach would be to create a standalone
skb-debugging config option.  There's quite a lot of debug stuff in there
which could be made conditional on that option.

But otoh, skb-debugging finds bugs.