linux-kernel - Re: [PATCH net-next v2] trace: tcp: Add tracepoint for tcp_cwnd

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Message-ID: <cc84f98f-d3d6-499e-9d2f-47eaeb56aad3@redhat.com>
Date: Tue, 18 Feb 2025 13:53:15 +0100
From: Paolo Abeni <pabeni@...hat.com>
To: Breno Leitao <leitao@...ian.org>
Cc: netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
 Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
 linux-trace-kernel@...r.kernel.org, kernel-team@...a.com,
 Jakub Kicinski <kuba@...nel.org>, Eric Dumazet <edumazet@...gle.com>,
 David Ahern <dsahern@...nel.org>, Steven Rostedt <rostedt@...dmis.org>,
 Masami Hiramatsu <mhiramat@...nel.org>, "David S. Miller"
 <davem@...emloft.net>, Simon Horman <horms@...nel.org>,
 Neal Cardwell <ncardwell@...gle.com>
Subject: Re: [PATCH net-next v2] trace: tcp: Add tracepoint for
 tcp_cwnd_reduction()

Hi,

On 2/14/25 6:07 PM, Breno Leitao wrote:
> Add a lightweight tracepoint to monitor TCP congestion window
> adjustments via tcp_cwnd_reduction(). This tracepoint enables tracking
> of:
> - TCP window size fluctuations
> - Active socket behavior
> - Congestion window reduction events
> 
> Meta has been using BPF programs to monitor this function for years.
> Adding a proper tracepoint provides a stable API for all users who need
> to monitor TCP congestion window behavior.
> 
> Use DECLARE_TRACE instead of TRACE_EVENT to avoid creating trace event
> infrastructure and exporting to tracefs, keeping the implementation
> minimal. (Thanks Steven Rostedt)
> 
> 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_cwnd_reduction_tp {
> 		....
> 	}
> 
> Signed-off-by: Breno Leitao <leitao@...ian.org>
> ---
> ---
> Changes in v2:
> - Close the parenthesis in a new line to honor the tcp.h format (Jakub).
> - Add the bpftrace example in the commit message (Jakub)
> - Link to v1: https://lore.kernel.org/r/20250207-cwnd_tracepoint-v1-1-13650f3ca96d@debian.org

For future similar situations, note that it's expected to carry-on the
tag already collected in the previous versions, since the delta is only
cosmetic.

No further actions required on your side.

Cheers,

Paolo