netdev - Re: [PATCH net] ipv4: set transport header earlier

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Date:	Tue, 16 Jul 2013 17:24:48 +0400
From:	Sergei Shtylyov <sergei.shtylyov@...entembedded.com>
To:	Eric Dumazet <eric.dumazet@...il.com>
CC:	David Miller <davem@...emloft.net>,
	netdev <netdev@...r.kernel.org>,
	Neal Cardwell <ncardwell@...gle.com>,
	netfilter-devel@...r.kernel.org, Tom Herbert <therbert@...gle.com>
Subject: Re: [PATCH net] ipv4: set transport header earlier

Hello.

On 16-07-2013 7:03, Eric Dumazet wrote:

> From: Eric Dumazet <edumazet@...gle.com>

> commit 45f00f99d6e ("ipv4: tcp: clean up tcp_v4_early_demux()") added a
> performance regression for non GRO traffic, basically disabling
> IP early demux.

> IPv6 stack resets transport header in ip6_rcv() before calling
> IP early demux in ip6_rcv_finish(), while IPv4 does this only in
> ip_local_deliver_finish(), _after_ IP early demux.

> GRO traffic happened to enable IP early demux because transport header
> is also set in inet_gro_receive()

> Instead of reverting the faulty commit, we can make IPv4/IPv6 behave the
> same : transport_header should be set in ip_rcv() instead of
> ip_local_deliver_finish()

> ip_local_deliver_finish() can also use skb_network_header_len() which is
> faster than ip_hdrlen()

> Signed-off-by: Eric Dumazet <edumazet@...gle.com>
> Cc: Neal Cardwell <ncardwell@...gle.com>
> Cc: Tom Herbert <therbert@...gle.com>
> ---
>   net/ipv4/ip_input.c |    7 +++----
>   1 file changed, 3 insertions(+), 4 deletions(-)

> diff --git a/net/ipv4/ip_input.c b/net/ipv4/ip_input.c
> index 3da817b..15e3e68 100644
> --- a/net/ipv4/ip_input.c
> +++ b/net/ipv4/ip_input.c
[...]
> @@ -437,6 +434,8 @@ int ip_rcv(struct sk_buff *skb, struct net_device *dev, struct packet_type *pt,
>   		goto drop;
>   	}
>
> +	skb->transport_header = skb->network_header + iph->ihl*4;

    Spaces around * wouldn't hurt, to be consistent with the rest of the 
statement and the Linux style in common.

WBR, Sergei

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