Re: [PATCH v3 net-next] net: introduce dev_set_forwarding()

Eric Dumazet
2013-11-04T13:58:23Z

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.