Re: reasons for dev_alloc_skb +16?

[Jeff Garzik <jgarzik@xxxxxxxxx>]

On Wed, Jul 09, 2003 at 05:53:55PM +0200, Andi Kleen wrote:
> On Wed, 9 Jul 2003 11:25:53 -0400
> Jeff Garzik <jgarzik@xxxxxxxxx> wrote:
> 
> > I knew this at one time, but have forgotten it :)
> > 
> > What is the reason for adding 16 to the dev_alloc_skb length?
> > (and skb_reserve of the same length)
> 
> For the skb_reserve alignment to align the IP header. 
> 
> But it's not clear it is still a good idea because it leads to cache line 
> misalignment of the beginning of the packet, forcing the card to do a
> costly Read-Modify-Write cycle.

Exactly.  Ben H is running into this, and pondering direct use of
alloc_skb for precisely this reason.

        Jeff