netdev - Re: [PATCH net-next] netdevice.h: Align struct netdevices members

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Message-ID: <1304999595.3050.45.camel@edumazet-laptop>
Date:	Tue, 10 May 2011 05:53:15 +0200
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Joe Perches <joe@...ches.com>
Cc:	David Miller <davem@...emloft.net>, netdev <netdev@...r.kernel.org>
Subject: Re: [PATCH net-next] netdevice.h: Align struct netdevices members

Le lundi 09 mai 2011 à 20:42 -0700, Joe Perches a écrit :
> Save a bit of space.
> 
> Signed-off-by: Joe Perches <joe@...ches.com>
> ---
>  include/linux/netdevice.h |    8 ++++----
>  1 files changed, 4 insertions(+), 4 deletions(-)
> 

Hmm... correct alignements are far more important for this structure.

Did you run benchmarks on 32bit and 64bit platforms ?

BTW we have ____cacheline_aligned_in_smp markers, I am not even sure
this patch saves space.

> diff --git a/include/linux/netdevice.h b/include/linux/netdevice.h
> index d5de66a..0fcb86b 100644
> --- a/include/linux/netdevice.h
> +++ b/include/linux/netdevice.h
> @@ -1020,9 +1020,6 @@ struct net_device {
>  	 *	part of the usual set specified in Space.c.
>  	 */
>  
> -	unsigned char		if_port;	/* Selectable AUI, TP,..*/
> -	unsigned char		dma;		/* DMA channel		*/
> -
>  	unsigned long		state;
>  
>  	struct list_head	dev_list;
> @@ -1141,13 +1138,16 @@ struct net_device {
>  	const struct header_ops *header_ops;
>  
>  	unsigned int		flags;	/* interface flags (a la BSD)	*/
> +	unsigned int		priv_flags; /* Like 'flags' but invisible to userspace. */
>  	unsigned short		gflags;
> -        unsigned int            priv_flags; /* Like 'flags' but invisible to userspace. */
>  	unsigned short		padded;	/* How much padding added by alloc_netdev() */
>  
>  	unsigned char		operstate; /* RFC2863 operstate */
>  	unsigned char		link_mode; /* mapping policy to operstate */
>  
> +	unsigned char		if_port;	/* Selectable AUI, TP,..*/
> +	unsigned char		dma;		/* DMA channel		*/
> +
>  	unsigned int		mtu;	/* interface MTU value		*/
>  	unsigned short		type;	/* interface hardware type	*/
>  	unsigned short		hard_header_len;	/* hardware hdr length	*/
> 


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