linux-kernel - Re: [PATCH net-next] trace: tcp: Add tracepoint for tcp

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Message-ID:
 <SA3PR15MB5630CFBB36C212008DA8ACC7CAC02@SA3PR15MB5630.namprd15.prod.outlook.com>
Date: Mon, 24 Feb 2025 19:12:59 +0000
From: Yonghong Song <yhs@...a.com>
To: Eric Dumazet <edumazet@...gle.com>, Breno Leitao <leitao@...ian.org>
CC: Neal Cardwell <ncardwell@...gle.com>,
        Kuniyuki Iwashima
	<kuniyu@...zon.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Masami Hiramatsu
	<mhiramat@...nel.org>,
        Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
        "David S. Miller" <davem@...emloft.net>,
        David Ahern <dsahern@...nel.org>, "kuba@...nel.org" <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>, Simon
 Horman <horms@...nel.org>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-trace-kernel@...r.kernel.org" <linux-trace-kernel@...r.kernel.org>,
        Kernel Team <kernel-team@...a.com>,
        "yonghong.song@...ux.dev"
	<yonghong.song@...ux.dev>
Subject: Re: [PATCH net-next] trace: tcp: Add tracepoint for tcp_sendmsg()

> ________________________________________
>
> On Mon, Feb 24, 2025 at 7:24 PM Breno Leitao <leitao@...ian.org> wrote:
>>
>> Add a lightweight tracepoint to monitor TCP sendmsg operations, enabling
>> the tracing of TCP messages being sent.
>>
>> Meta has been using BPF programs to monitor this function for years,
>> indicating significant interest in observing this important
>> functionality. Adding a proper tracepoint provides a stable API for all
>> users who need visibility into TCP message transmission.
>>
>> The implementation uses DECLARE_TRACE instead of TRACE_EVENT to avoid
>> creating unnecessary trace event infrastructure and tracefs exports,
>> keeping the implementation minimal while stabilizing the API.
>>
>> Given that this patch creates a rawtracepoint, you could hook into it
>> using regular tooling, like bpftrace, using regular rawtracepoint
>> infrastructure, such as:
>>
>>         rawtracepoint:tcp_sendmsg_tp {
>>                 ....
>>         }
>
> I would expect tcp_sendmsg() being stable enough ?
>
> kprobe:tcp_sendmsg {
> }

In LTO mode, tcp_sendmsg could be inlined cross files. For example,

  net/ipv4/tcp.c: 
       int tcp_sendmsg(struct sock *sk, struct msghdr *msg, size_t size)
  net/ipv4/tcp_bpf.c:
       ...
      return tcp_sendmsg(sk, msg, size);
  net/ipv6/af_inet6.c:
       ...
       return INDIRECT_CALL_2(prot->sendmsg, tcp_sendmsg, udpv6_sendmsg, ...)

And this does happen in our production environment.