Re: [PATCH net-next v2 1/2] net: netfilter: Add IPIP flowtable SW acceleration

[Lorenzo Bianconi <lorenzo@kernel.org>]

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> On 6/28/25 11:47 AM, Lorenzo Bianconi wrote:
> >> On Fri, Jun 27, 2025 at 02:45:28PM +0200, Lorenzo Bianconi wrote:
> >>> Introduce SW acceleration for IPIP tunnels in the netfilter flowtable
> >>> infrastructure.
> >>> IPIP SW acceleration can be tested running the following scenario where
> >>> the traffic is forwarded between two NICs (eth0 and eth1) and an IPIP
> >>> tunnel is used to access a remote site (using eth1 as the underlay device):
> >>>
> >>> ETH0 -- TUN0 <==> ETH1 -- [IP network] -- TUN1 (192.168.100.2)
> >>>
> >>> $ip addr show
> >>> 6: eth0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc noqueue state UP group default qlen 1000
> >>>     link/ether 00:00:22:33:11:55 brd ff:ff:ff:ff:ff:ff
> >>>     inet 192.168.0.2/24 scope global eth0
> >>>        valid_lft forever preferred_lft forever
> >>> 7: eth1: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc noqueue state UP group default qlen 1000
> >>>     link/ether 00:11:22:33:11:55 brd ff:ff:ff:ff:ff:ff
> >>>     inet 192.168.1.1/24 scope global eth1
> >>>        valid_lft forever preferred_lft forever
> >>> 8: tun0@NONE: <POINTOPOINT,NOARP,UP,LOWER_UP> mtu 1480 qdisc noqueue state UNKNOWN group default qlen 1000
> >>>     link/ipip 192.168.1.1 peer 192.168.1.2
> >>>     inet 192.168.100.1/24 scope global tun0
> >>>        valid_lft forever preferred_lft forever
> >>>
> >>> $ip route show
> >>> default via 192.168.100.2 dev tun0
> >>> 192.168.0.0/24 dev eth0 proto kernel scope link src 192.168.0.2
> >>> 192.168.1.0/24 dev eth1 proto kernel scope link src 192.168.1.1
> >>> 192.168.100.0/24 dev tun0 proto kernel scope link src 192.168.100.1
> >>>
> >>> $nft list ruleset
> >>> table inet filter {
> >>>         flowtable ft {
> >>>                 hook ingress priority filter
> >>>                 devices = { eth0, eth1 }
> >>>         }
> >>>
> >>>         chain forward {
> >>>                 type filter hook forward priority filter; policy accept;
> >>>                 meta l4proto { tcp, udp } flow add @ft
> >>>         }
> >>> }
> >>
> >> Is there a proof that this accelerates forwarding?
> > 
> > I reproduced the scenario described above using veths (something similar to
> > what is done in nft_flowtable.sh) and I got the following results:
> > 
> > - flowtable configured as above between the two router interfaces
> > - TCP stream between client and server going via the IPIP tunnel
> > - TCP stream transmitted into the IPIP tunnel:
> >   - net-next:				~41Gbps
> >   - net-next + IPIP flowtbale support:	~40Gbps
> > - TCP stream received from the IPIP tunnel:
> >   - net-next:				~35Gbps
> >   - net-next + IPIP flowtbale support:	~49Gbps
> > 
> >>
> >>> Signed-off-by: Lorenzo Bianconi <lorenzo@kernel.org>
> >>> ---
> >>>  net/ipv4/ipip.c                  | 21 +++++++++++++++++++++
> >>>  net/netfilter/nf_flow_table_ip.c | 28 ++++++++++++++++++++++++++--
> >>>  2 files changed, 47 insertions(+), 2 deletions(-)
> >>>
> > 
> > [...]
> > 
> >>>  static bool nf_flow_skb_encap_protocol(struct sk_buff *skb, __be16 proto,
> >>>  				       u32 *offset)
> >>>  {
> >>>  	struct vlan_ethhdr *veth;
> >>>  	__be16 inner_proto;
> >>> +	u16 size;
> >>>  
> >>>  	switch (skb->protocol) {
> >>> +	case htons(ETH_P_IP):
> >>> +		if (nf_flow_ip4_encap_proto(skb, &size))
> >>> +			*offset += size;
> >>
> >> This is blindly skipping the outer IP header.
> > 
> > Do you mean we are supposed to validate the outer IP header performing the
> > sanity checks done in nf_flow_tuple_ip()?
> 
> Yes.

ack

> 
> Note that we could always obtain a possibly considerably tput
> improvement stripping required validation ;)

I have been proactive and I added the sanity checks done in nf_flow_tuple_ip()
and I got ~ the same results.

> 
> I guess this should go via the netfilter tree, please adjust the patch
> prefix accordingly.

ack

> 
> Also why IP over IP specifically? I guess other kind of encapsulations
> may benefit from similar path and are more ubiquitous.

this is just the first step, I want to add IPv6 counterpart too.

Regards,
Lorenzo

> 
> 
> /P
> 

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