linux-kernel - Re: [PATCH bpf-next] tcp: bpf: Add TCP_BPF_RCV_SSTHRESH for bpf

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Date:   Tue, 11 Jan 2022 13:47:49 -0800
From:   Song Liu <song@...nel.org>
To:     Ivan Babrou <ivan@...udflare.com>
Cc:     bpf <bpf@...r.kernel.org>, Networking <netdev@...r.kernel.org>,
        open list <linux-kernel@...r.kernel.org>,
        kernel-team@...udflare.com, Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Andrii Nakryiko <andrii@...nel.org>,
        Martin KaFai Lau <kafai@...com>,
        Eric Dumazet <edumazet@...gle.com>
Subject: Re: [PATCH bpf-next] tcp: bpf: Add TCP_BPF_RCV_SSTHRESH for bpf_setsockopt

On Tue, Jan 11, 2022 at 11:29 AM Ivan Babrou <ivan@...udflare.com> wrote:
>
> This patch adds bpf_setsockopt(TCP_BPF_RCV_SSTHRESH) to allow setting
> rcv_ssthresh value for TCP connections. Combined with increased
> window_clamp via tcp_rmem[1], it allows to advertise initial scaled
> TCP window larger than 64k. This is useful for high BDP connections,
> where it allows to push data with fewer roundtrips, reducing latency.
>
> For active connections the larger window is advertised in the first
> non-SYN ACK packet as the part of the 3 way handshake.
>
> For passive connections the larger window is advertised whenever
> there's any packet to send after the 3 way handshake.
>
> See: https://lkml.org/lkml/2021/12/22/652

I guess this is [1] mentioned above. Please use lore link instead, e.g.

[1] https://lore.kernel.org/all/CABWYdi0qBQ57OHt4ZbRxMtdSzhubzkPaPKkYzdNfu4+cgPyXCA@mail.gmail.com/

Can we add a selftests for this? Something similar to

tools/testing/selftests/bpf/progs/test_misc_tcp_hdr_options.c

Thanks,
Song

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