netdev - Re: [PATCH bpf-next v2 07/11] bpf: tcp: Support tcp_congestion

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Date:   Mon, 23 Dec 2019 20:18:25 +0000
From:   Yonghong Song <yhs@...com>
To:     Martin Lau <kafai@...com>,
        "bpf@...r.kernel.org" <bpf@...r.kernel.org>
CC:     Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        David Miller <davem@...emloft.net>,
        Kernel Team <Kernel-team@...com>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>
Subject: Re: [PATCH bpf-next v2 07/11] bpf: tcp: Support tcp_congestion_ops in
 bpf



On 12/20/19 10:26 PM, Martin KaFai Lau wrote:
> This patch makes "struct tcp_congestion_ops" to be the first user
> of BPF STRUCT_OPS.  It allows implementing a tcp_congestion_ops
> in bpf.
> 
> The BPF implemented tcp_congestion_ops can be used like
> regular kernel tcp-cc through sysctl and setsockopt.  e.g.
> [root@...h-fb-vm1 bpf]# sysctl -a | egrep congestion
> net.ipv4.tcp_allowed_congestion_control = reno cubic bpf_cubic
> net.ipv4.tcp_available_congestion_control = reno bic cubic bpf_cubic
> net.ipv4.tcp_congestion_control = bpf_cubic
> 
> There has been attempt to move the TCP CC to the user space
> (e.g. CCP in TCP).   The common arguments are faster turn around,
> get away from long-tail kernel versions in production...etc,
> which are legit points.
> 
> BPF has been the continuous effort to join both kernel and
> userspace upsides together (e.g. XDP to gain the performance
> advantage without bypassing the kernel).  The recent BPF
> advancements (in particular BTF-aware verifier, BPF trampoline,
> BPF CO-RE...) made implementing kernel struct ops (e.g. tcp cc)
> possible in BPF.  It allows a faster turnaround for testing algorithm
> in the production while leveraging the existing (and continue growing)
> BPF feature/framework instead of building one specifically for
> userspace TCP CC.
> 
> This patch allows write access to a few fields in tcp-sock
> (in bpf_tcp_ca_btf_struct_access()).
> 
> The optional "get_info" is unsupported now.  It can be added
> later.  One possible way is to output the info with a btf-id
> to describe the content.
> 
> Signed-off-by: Martin KaFai Lau <kafai@...com>

Ack from bpf/btf perspective.

Acked-by: Yonghong Song <yhs@...com>