linux-kernel - Re: [RFC] Documentation about unaligned memory access

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Message-ID: <20071127004016.GD4684@ghostprotocols.net>
Date:	Mon, 26 Nov 2007 22:40:16 -0200
From:	"Arnaldo Carvalho de Melo" <acme@...hat.com>
To:	Johannes Berg <johannes@...solutions.net>
Cc:	Daniel Drake <dsd@...too.org>, linux-kernel@...r.kernel.org,
	davem@...emloft.net, kune@...ne-taler.de
Subject: Re: [RFC] Documentation about unaligned memory access

Em Mon, Nov 26, 2007 at 03:47:06PM +0100, Johannes Berg escreveu:
> 
> > Sidenote: in the above example, you may wish to reorder the fields in the
> > above structure so that the overall structure uses less memory. For example,
> > moving field3 to sit inbetween field1 and field2 (where the padding is
> > inserted) would shrink the overall structure by 1 byte:
> > 
> > 	struct foo {
> > 		u16 field1;
> > 		u8 field3;
> > 		u32 field2;
> > 	};
> 
> You can reorder to u32, u16, u8 order and save another byte :)
> 
> A reference to pahole could be appropriate here, and probably a small
> note that some large existing structures like netdev have deliberate
> holes to achieve cache alignment.

shameless plug:

https://ols2006.108.redhat.com/2007/Reprints/melo-Reprint.pdf

- Arnaldo
-
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