netdev - Re: [PATCHv2 net-next 00/10] net: support ipv4 big tcp

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Date:   Tue, 24 Jan 2023 18:25:50 +0100
From:   Eric Dumazet <edumazet@...gle.com>
To:     Xin Long <lucien.xin@...il.com>
Cc:     network dev <netdev@...r.kernel.org>, davem@...emloft.net,
        kuba@...nel.org, Paolo Abeni <pabeni@...hat.com>,
        David Ahern <dsahern@...il.com>,
        Hideaki YOSHIFUJI <yoshfuji@...ux-ipv6.org>,
        Pravin B Shelar <pshelar@....org>,
        Jamal Hadi Salim <jhs@...atatu.com>,
        Cong Wang <xiyou.wangcong@...il.com>,
        Jiri Pirko <jiri@...nulli.us>,
        Pablo Neira Ayuso <pablo@...filter.org>,
        Florian Westphal <fw@...len.de>,
        Marcelo Ricardo Leitner <marcelo.leitner@...il.com>,
        Ilya Maximets <i.maximets@....org>,
        Aaron Conole <aconole@...hat.com>,
        Roopa Prabhu <roopa@...dia.com>,
        Nikolay Aleksandrov <razor@...ckwall.org>,
        Mahesh Bandewar <maheshb@...gle.com>,
        Paul Moore <paul@...l-moore.com>,
        Guillaume Nault <gnault@...hat.com>
Subject: Re: [PATCHv2 net-next 00/10] net: support ipv4 big tcp

On Tue, Jan 24, 2023 at 6:14 PM Xin Long <lucien.xin@...il.com> wrote:
>
> On Tue, Jan 24, 2023 at 11:35 AM Eric Dumazet <edumazet@...gle.com> wrote:
> >
> > On Tue, Jan 24, 2023 at 4:51 PM Xin Long <lucien.xin@...il.com> wrote:
> > >
> > > On Tue, Jan 24, 2023 at 3:27 AM Eric Dumazet <edumazet@...gle.com> wrote:
> > > >
> > > > On Tue, Jan 24, 2023 at 3:20 AM Xin Long <lucien.xin@...il.com> wrote:
> > > > >
> > > > > This is similar to the BIG TCP patchset added by Eric for IPv6:
> > > > >
> > > > >   https://lwn.net/Articles/895398/
> > > > >
> > > > > Different from IPv6, IPv4 tot_len is 16-bit long only, and IPv4 header
> > > > > doesn't have exthdrs(options) for the BIG TCP packets' length. To make
> > > > > it simple, as David and Paolo suggested, we set IPv4 tot_len to 0 to
> > > > > indicate this might be a BIG TCP packet and use skb->len as the real
> > > > > IPv4 total length.
> > > > >
> > > > > This will work safely, as all BIG TCP packets are GSO/GRO packets and
> > > > > processed on the same host as they were created; There is no padding
> > > > > in GSO/GRO packets, and skb->len - network_offset is exactly the IPv4
> > > > > packet total length; Also, before implementing the feature, all those
> > > > > places that may get iph tot_len from BIG TCP packets are taken care
> > > > > with some new APIs:
> > > > >
> > > > > Patch 1 adds some APIs for iph tot_len setting and getting, which are
> > > > > used in all these places where IPv4 BIG TCP packets may reach in Patch
> > > > > 2-8, and Patch 9 implements this feature and Patch 10 adds a selftest
> > > > > for it.
> > > > >
> > > > > Note that the similar change as in Patch 2-6 are also needed for IPv6
> > > > > BIG TCP packets, and will be addressed in another patchset.
> > > > >
> > > > > The similar performance test is done for IPv4 BIG TCP with 25Gbit NIC
> > > > > and 1.5K MTU:
> > > > >
> > > > > No BIG TCP:
> > > > > for i in {1..10}; do netperf -t TCP_RR -H 192.168.100.1 -- -r80000,80000 -O MIN_LATENCY,P90_LATENCY,P99_LATENCY,THROUGHPUT|tail -1; done
> > > > > 168          322          337          3776.49
> > > > > 143          236          277          4654.67
> > > > > 128          258          288          4772.83
> > > > > 171          229          278          4645.77
> > > > > 175          228          243          4678.93
> > > > > 149          239          279          4599.86
> > > > > 164          234          268          4606.94
> > > > > 155          276          289          4235.82
> > > > > 180          255          268          4418.95
> > > > > 168          241          249          4417.82
> > > > >
> > > >
> > > > NACK again
> > > >
> > > > You have not addressed my feedback.
> > > >
> > > > Given the experimental nature of BIG TCP, we need separate netlink attributes,
> > > > so that we can selectively enable BIG TCP for IPV6, and not for IPV4.
> > > >
> > > That will be some change, and I will try to work on it.
> > >
> > > While at it, just try to be clearer, about the fixes for IPv6 BIG TCP
> > > I mentioned in this patchset. Since skb->len is trustable for GSO TCP
> > > packets. Are you still not okay with checking the skb_ipv6_pktlen()
> > > API added to fix them in netfilter/tc/bridge/openvswitch?
> > >
> >
> > Are you speaking of length_mt6() ?
> Yes, but not only there, see also:
>
> [1]:
> dump_ipv6_packet()
> nf_ct_bridge_pre()
> ovs_skb_network_trim()/tcf_ct_skb_network_trim()
> cake_ack_filter()
>
> These places get pktlen directly from ipv6_hdr(skb)->payload_len.

dump_ipv6_packet() is right if its intent is to 'dump header values'
If jumbo is not yet parsed, this should be added.

cake_ack_filter() depends on receiving non malicious packets, which is
not guaranteed.

Special casing GSO seems the wrong way to fix buggy spots like these.