netdev - Re: [RFC 2/2] shrink size of scatterlist on common i386/x86-64

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Message-ID: <20070705170051.37ff2ab8@freepuppy.localdomain.hemminger.net>
Date:	Thu, 5 Jul 2007 17:00:51 -0700
From:	Stephen Hemminger <shemminger@...ux-foundation.org>
To:	David Miller <davem@...emloft.net>
Cc:	netdev@...r.kernel.org
Subject: Re: [RFC 2/2] shrink size of scatterlist on common i386/x86-64

On Thu, 05 Jul 2007 16:43:08 -0700 (PDT)
David Miller <davem@...emloft.net> wrote:

> From: Stephen Hemminger <shemminger@...ux-foundation.org>
> Date: Thu, 05 Jul 2007 16:14:14 -0700
> 
> > The scatterlist only needs 16 bits for length/offset because
> > PAGE_SIZE is 4K
> > 
> > Signed-off-by: Stephen Hemminger <shemminger@...ux-foundation.org>
> 
> Unfortunately I don't think this can be done, even on i386.
> 
> It is legal to use order!=0 pages and multi-page areas in a single
> scatterlist entry.
> 

Okay, but then using SG lists makes skbuff's much bigger.
    
	fraglist	scatterlist		   per skbuff
32 bit	8		20		+12 * 18 = +216!
64 bit	16		32		+16 * 18 = +288

So never mind...

I'll do a fraglist to scatter list set of routines, but not sure
if it's worth it.


-- 
Stephen Hemminger <shemminger@...ux-foundation.org>
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