netdev - Re: [PATCH nf-next] netfilter: nfnetlink

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Date:	Mon, 18 Mar 2013 06:51:19 -0700
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Florian Westphal <fw@...len.de>
Cc:	Pablo Neira Ayuso <pablo@...filter.org>,
	netdev <netdev@...r.kernel.org>,
	Netfilter Developer Mailing List 
	<netfilter-devel@...r.kernel.org>
Subject: Re: [PATCH nf-next] netfilter: nfnetlink_queue: zero copy support

On Mon, 2013-03-18 at 10:24 +0100, Florian Westphal wrote:
> Eric Dumazet <eric.dumazet@...il.com> wrote:
> >
> > -GRO/GSO packets are segmented in nf_queue()
> > and checksummed in nfqnl_build_packet_message().
> > Proper support for GSO/GRO packets (no segmentation,
> > and no checksumming) needs application cooperation, if we
> > want no regressions.
> 
> Since ipqueue is gone we might be able to push the segmentation
> down to nfnetlink_queue.  Then new userspace applications
> could indicate a 'I won't verify checksums and will handle huge
> packets'.
> 
> Are you working on something like this?

I validated that it was only an API concern, by commenting out the code,
and got 20Gbps (link speed) using the sample program (using a bigger
buffer to receive the skbs and removing the printf() for each packet)

Pablo followed the experiments and I believe he has an idea of the
needed API. Anyway, after one week in NFWS, I wont have the time to do
it, I have a huge backlog...

Note that its not a zero copy :

Before the patch we had 2 copies. (kernel->kernel done in softirq
context, and kernel->user in process context)

After the patch we have the copy from kernel to user land, done
in process context.



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