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

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Message-ID: <559f3da9-4b3d-41c2-bf44-18329f76e937@kernel.org>
Date: Mon, 24 Feb 2025 12:16:04 -0700
From: David Ahern <dsahern@...nel.org>
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>, Jakub Kicinski <kuba@...nel.org>,
 Paolo Abeni <pabeni@...hat.com>, Simon Horman <horms@...nel.org>,
 netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
 linux-trace-kernel@...r.kernel.org, kernel-team@...a.com,
 yonghong.song@...ux.dev
Subject: Re: [PATCH net-next] trace: tcp: Add tracepoint for tcp_sendmsg()

On 2/24/25 12:03 PM, Eric Dumazet wrote:
> 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 {
> }

Also, if a tracepoint is added, inside of tcp_sendmsg_locked would cover
more use cases (see kernel references to it).

We have a patch for a couple years now with a tracepoint inside the

while (msg_data_left(msg)) {
}

loop which is more useful than just entry to sendmsg.