netdev - Re: [PATCH v3 net-next] net: introduce dev_set

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Date:	Mon, 04 Nov 2013 05:58:21 -0800
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Herbert Xu <herbert@...dor.apana.org.au>
Cc:	Ben Hutchings <bhutchings@...arflare.com>,
	David Miller <davem@...emloft.net>,
	christoph.paasch@...ouvain.be, netdev@...r.kernel.org,
	hkchu@...gle.com, mwdalton@...gle.com
Subject: Re: [PATCH v3 net-next] net: introduce dev_set_forwarding()

On Mon, 2013-11-04 at 15:21 +0800, Herbert Xu wrote:
> On Sun, Nov 03, 2013 at 11:10:41PM -0800, Eric Dumazet wrote:
> >
> > Using frag_list for skb meant to be delivered to local stack is mostly
> > fine. Its for forwarding that its not a win, since no driver actually
> > supports frag_list and we revert to skb_segment().
> 
> Sigh.
> 
> Most of the gain these days isn't coming from the hardware anymore,
> especially for virtualisation where the network stack is at least
> twice as long.  The gain is in paying the cost of the network once
> instead of n times for an aggregation of n packets.  So with your
> mega-GRO patch, the choice comes down to paying for one trip or
> three trips.  The difference may not be trivial, even for a router.

I do think we are on the same thoughts.

Please take a look at 2613af0ed18a11d5c566a81f9a6510b73180660a
("virtio_net: migrate mergeable rx buffers to page frag allocators")

Notice it also uses frag_list

So if you don't provide a skb_segment() patch, I will.

I had urgent matters last week.


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