Re: [ath9k-devel] [PATCH 1/3] ath9k: Decrease skb size to fit into one page.

[Johannes Berg <johannes@sipsolutions.net>]

On Fri, 2011-01-07 at 14:46 -0800, Ben Greear wrote:
> On 01/07/2011 02:26 PM, Eric Dumazet wrote:
> > Le vendredi 07 janvier 2011 à 14:20 -0800, Ben Greear a écrit :
> >> On 0
> >>> Using skb_copy() is wrong then, since it makes a copy (order-1
> >>> allocations)
> >>>
> >>> It should use :
> >>>    skb_alloc( actual_size_of_frame  not the 3840 thing ...)
> >>>    copy(data)
> >>
> >> We need the extra stuff copied too I think (like skb->cb).
> >>
> >> If you could provide a bit more complete example code, I'll be happy
> >> to test it...
> >
> > take a random drivers/net using copybreak ... say ... tg3.c
> >
> > lines 4785
> >
> > len = length_of_the_current_frame
> > copy_skb = netdev_alloc_skb(...,  len);
> > // allocates exact required size not a byte more....
> > ...
> > skb_copy_from_linear_data(skb, copy_skb->data, len);
> > ...
> > skb_put(skb, len);
> > ...
> 
> That seems fine for drivers, but I'm guessing something different
> would be needed in the mac80211/rx.c code:
> 
> I figure doing the fix here might be a nice quick fix,
> and would help with all funky drivers.  Later, can fix the
> ath9k to do the skb copying as soon as DMA is done?

This code in mac80211 that you point out will nearly never do a copy
unless you have a lot of multicast traffic. I really don't think it
makes sense to think about changing that now.

johannes