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

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Message-ID: <807503bf-4213-4423-b38b-ffdc11aaaeee@redhat.com>
Date: Thu, 3 Jul 2025 10:25:26 +0200
From: Paolo Abeni <pabeni@...hat.com>
To: Lorenzo Bianconi <lorenzo.bianconi@...hat.com>,
 Pablo Neira Ayuso <pablo@...filter.org>
Cc: Lorenzo Bianconi <lorenzo@...nel.org>,
 "David S. Miller" <davem@...emloft.net>, David Ahern <dsahern@...nel.org>,
 Eric Dumazet <edumazet@...gle.com>, Jakub Kicinski <kuba@...nel.org>,
 Simon Horman <horms@...nel.org>, Jozsef Kadlecsik <kadlec@...filter.org>,
 Shuah Khan <shuah@...nel.org>, netdev@...r.kernel.org,
 netfilter-devel@...r.kernel.org, coreteam@...filter.org,
 linux-kselftest@...r.kernel.org
Subject: Re: [PATCH net-next v2 1/2] net: netfilter: Add IPIP flowtable SW
 acceleration

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@...E: <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@...nel.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.

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

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

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


/P