netdev - Re: [PATCH net-next-2.6] net: pskb_expand

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Message-ID: <20100920091425.GA8381@ff.dom.local>
Date:	Mon, 20 Sep 2010 09:14:26 +0000
From:	Jarek Poplawski <jarkao2@...il.com>
To:	Eric Dumazet <eric.dumazet@...il.com>
Cc:	David Miller <davem@...emloft.net>, netdev@...r.kernel.org
Subject: Re: [PATCH net-next-2.6] net: pskb_expand_head() optimization

On Mon, Sep 20, 2010 at 11:02:00AM +0200, Eric Dumazet wrote:
> Le lundi 20 septembre 2010 ?? 07:21 +0000, Jarek Poplawski a écrit :
> 
> > Probably we could start from enhacing moving drivers to paged skbs
> > where possible. And maybe simplifying the skb model by not allowing
> > frags and frag lists together?
> > 
> 
> Sure. I believe current model, pre-allocating skb in huge tx rings is a
> waste of mem bandwidth anyway. (I am refering to the struct sk_buff
> itself, not the payload part)
> 
> Of course some drivers are doing it right, using netdev_alloc_skb()
> right before feeding this skb to network stack, not an old one.
> 
> > Btw, I wonder what is the exact reason we can't use only
> > NET_SKBUFF_DATA_USES_OFFSET?
> 
> I see no real reason.
> 
> On 32bit arches, it might be faster to manipulate pointers, and not
> 'base+offset' values.

The only reason is code readability and maintenance. Did anybody check
how much faster?

Jarek P.
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