netdev - Re: [net-next 02/11] ixgbe: Mask off check of frag

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Date:	Fri, 12 Apr 2013 13:29:44 -0700
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Alexander Duyck <alexander.h.duyck@...el.com>
Cc:	Jeff Kirsher <jeffrey.t.kirsher@...el.com>, davem@...emloft.net,
	netdev@...r.kernel.org, gospo@...hat.com, sassmann@...hat.com
Subject: Re: [net-next 02/11] ixgbe: Mask off check of frag_off as we only
 want fragment offset

On Fri, 2013-04-12 at 13:12 -0700, Alexander Duyck wrote:

> I think part of the trouble is we are debating reworking the wrong
> function.  We would probably be better off if we could come up with a
> generic way to handle the ixgbe_pull_tail function.  I think the only
> complaint I would have in using the __skb_get_poff in there is the fact
> that it would be copying the header in multiple chunks.  If it worked
> more like GRO where it just used an offset in the first frag instead of
> having to copy the headers separately to read them then I would be 100%
> on board.

__skb_get_poff() does no copy at all if you provide a linear 'skb'

Its really fast, I am really sorry you have wrong idea of what is going
on.

static inline void *skb_header_pointer(const struct sk_buff *skb, int offset,
                                       int len, void *buffer)
{
        int hlen = skb_headlen(skb);

        if (hlen - offset >= len)
                return skb->data + offset;


On the other hand GRO engine is way more expensive, now you mention it, we might
use the flow dissector to speed it.



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