linux-kernel - Re: [PATCH net-next v7 RESEND] tcp: trace retransmit failures in tcp_retransmit

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Message-ID: <CANn89iJiLC6ZRXqJU82vsH0Lu+-o-GP_1WAK=2bcfdGmu7nKrg@mail.gmail.com>
Date: Mon, 21 Jul 2025 23:42:27 -0700
From: Eric Dumazet <edumazet@...gle.com>
To: fan.yu9@....com.cn
Cc: kuba@...nel.org, ncardwell@...gle.com, davem@...emloft.net, 
	dsahern@...nel.org, pabeni@...hat.com, horms@...nel.org, kuniyu@...gle.com, 
	rostedt@...dmis.org, mhiramat@...nel.org, mathieu.desnoyers@...icios.com, 
	netdev@...r.kernel.org, linux-kernel@...r.kernel.org, 
	linux-trace-kernel@...r.kernel.org, yang.yang29@....com.cn, 
	xu.xin16@....com.cn, tu.qiang35@....com.cn, jiang.kun2@....com.cn, 
	qiu.yutan@....com.cn, wang.yaxin@....com.cn, he.peilin@....com.cn
Subject: Re: [PATCH net-next v7 RESEND] tcp: trace retransmit failures in tcp_retransmit_skb

On Sun, Jul 20, 2025 at 8:16 PM <fan.yu9@....com.cn> wrote:
>
> From: Fan Yu <fan.yu9@....com.cn>
>
> Background
> ==========
> When TCP retransmits a packet due to missing ACKs, the
> retransmission may fail for various reasons (e.g., packets
> stuck in driver queues, receiver zero windows, or routing issues).
>
> The original tcp_retransmit_skb tracepoint:
>
>   'commit e086101b150a ("tcp: add a tracepoint for tcp retransmission")'
>
> lacks visibility into these failure causes, making production
> diagnostics difficult.
>
>

> Suggested-by: Jakub Kicinski <kuba@...nel.org>
> Suggested-by: Eric Dumazet <edumazet@...gle.com>
> Co-developed-by: xu xin <xu.xin16@....com.cn>
> Signed-off-by: xu xin <xu.xin16@....com.cn>
> Signed-off-by: Fan Yu <fan.yu9@....com.cn>
> Reviewed-by: Kuniyuki Iwashima <kuniyu@...gle.com>

Please do not add a Suggested-by tag when the original idea did not
come from someone else.

I only made suggestions to make your patch better.

Reviewed-by: Eric Dumazet <edumazet@...gle.com>