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

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Date:   Tue, 24 Jan 2023 09:27:01 +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 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.

Some of us do not have time to risk breaking IPV4, even if IPV4 for
our networks is less than 0.01 % of the traffic.