linux-kernel - Re: [PATCH net v2 1/3] net: gro: add {inner_}network_offset to napi_gro

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Date: Mon, 22 Apr 2024 12:56:23 -0400
From: Willem de Bruijn <willemdebruijn.kernel@...il.com>
To: Richard Gobert <richardbgobert@...il.com>, 
 Willem de Bruijn <willemdebruijn.kernel@...il.com>, 
 davem@...emloft.net, 
 edumazet@...gle.com, 
 kuba@...nel.org, 
 pabeni@...hat.com, 
 dsahern@...nel.org, 
 alexander.duyck@...il.com, 
 aleksander.lobakin@...el.com, 
 netdev@...r.kernel.org, 
 linux-kernel@...r.kernel.org
Subject: Re: [PATCH net v2 1/3] net: gro: add {inner_}network_offset to
 napi_gro_cb

Richard Gobert wrote:
> Willem de Bruijn wrote:
> > Richard Gobert wrote:
> >> This patch adds network_offset and inner_network_offset to napi_gro_cb, and
> >> makes sure both are set correctly. In the common path there's only one
> >> write (skb_gro_reset_offset, which replaces skb_set_network_header).
> >>
> >> Signed-off-by: Richard Gobert <richardbgobert@...il.com>
> >> ---
> >>  drivers/net/geneve.c           |  1 +
> >>  drivers/net/vxlan/vxlan_core.c |  1 +
> >>  include/net/gro.h              | 18 ++++++++++++++++--
> >>  net/8021q/vlan_core.c          |  2 ++
> >>  net/core/gro.c                 |  1 +
> >>  net/ethernet/eth.c             |  1 +
> >>  net/ipv4/af_inet.c             |  5 +----
> >>  net/ipv4/gre_offload.c         |  1 +
> >>  net/ipv6/ip6_offload.c         |  8 ++++----
> >>  9 files changed, 28 insertions(+), 10 deletions(-)
> >>
> > 
> >> +static inline int skb_gro_network_offset(const struct sk_buff *skb)
> >> +{
> >> +	return NAPI_GRO_CB(skb)->network_offsets[NAPI_GRO_CB(skb)->encap_mark];
> >> +}
> >> +
> > 
> > 
> >> @@ -236,8 +236,6 @@ INDIRECT_CALLABLE_SCOPE struct sk_buff *ipv6_gro_receive(struct list_head *head,
> >>  	if (unlikely(!iph))
> >>  		goto out;
> >>  
> >> -	skb_set_network_header(skb, off);
> >> -
> > 
> > Especially for net, this is still a large patch.
> > 
> > Can we avoid touching all those tunnel callbacks and just set the
> > offsets in inet_gro_receive and ipv6_gro_receive themselves, just
> > as skb_set_network_header now:
> > 
> > @@ -236,7 +236,7 @@ INDIRECT_CALLABLE_SCOPE struct sk_buff *ipv6_gro_receive(struct list_head *head,
> >         if (unlikely(!iph))
> >                 goto out;
> >  
> > -       skb_set_network_header(skb, off);
> > +       NAPI_GRO_CB(skb)->network_offsets[NAPI_GRO_CB(skb)->encap_mark] = off;
> > 
> 
> Thanks for the reply!
> 
> Setting network_offset on dev_gro_receive and inner_network_offset only
> in the tunnel callbacks is the best option IMO. I agree that
> we want a small patch to net that solves the problem, although I 
> think always using ->encap_mark in the common path is not ideal. 
>
> We can avoid changing all the tunnel callbacks by always setting
> inner_network_offset in {ipv6,inet}_gro_receive and initialize
> network_offset to 0 in dev_gro_receive. It will result in a small
> change, without using ->encap_mark.
> 
> What are your thoughts?

That works. It's a bit ugly that inner_network_offset will always be
set, even if a packet only traverses inet_gro_receive once. What is
your concern with testing encap_mark?

How do you want to detect in udp[46]_lib_lookup_skb which of the two
offsets to use? That would still be encap_mark based?