On Mon, Jun 30, 2025 at 1:05 AM <xu.xi...@zte.com.cn> wrote:
>
> From: Fan Yu <fan....@zte.com.cn>
>
> Problem
> =======
> When TCP retransmits a packet due to missing ACKs, the retransmission
> may fail for various reasons (e.g., packets stuck in driver queues,
> sequence errors, or routing issues). Currently, these failure reasons
> are internally handled in __tcp_retransmit_skb() but lack visibility to
> userspace, which makes it difficult to diagnose retransmission failures in
> production environments.
>
> Solution
> =======
> This patch adds a reason field to the tcp_retransmit_skb tracepoint,
> enumerating with explicit failure cases:
> TCP_RETRANS_IN_HOST_QUEUE (packet still queued in driver)
> TCP_RETRANS_END_SEQ_ERROR (invalid end sequence)
> TCP_RETRANS_TRIM_HEAD_NOMEM (trim head no memory)
> TCP_RETRANS_UNCLONE_NOMEM (skb unclone keeptruesize no memory)
> TCP_RETRANS_FRAG_NOMEM (fragment no memory)
> TCP_RETRANS_ROUTE_FAIL (routing failure)
> TCP_RETRANS_RCV_ZERO_WINDOW (closed recevier window)
> TCP_RETRANS_PSKB_COPY_NOBUFS (no buffer for skb copy)
> TCP_RETRANS_QUIT_UNDEFINED (quit reason undefined)
'undefined' ?
>
> Impact
> ======
> 1. Enables BPF programs to filter retransmission failures by reason.
> 2. Allows precise failure rate monitoring via ftrace.
>
> Co-developed-by: xu xin <xu.xi...@zte.com.cn>
> Signed-off-by: xu xin <xu.xi...@zte.com.cn>
> Signed-off-by: Fan Yu <fan....@zte.com.cn>
Problem is that this patch breaks the original trace point, without
any mention of the potential consequences in the changelog ?
commit e086101b150ae8e99e54ab26101ef3835fa9f48d
Author: Cong Wang <xiyou.wangc...@gmail.com>
Date: Fri Oct 13 13:03:16 2017 -0700
tcp: add a tracepoint for tcp retransmission
