netdev - Re: [Patch net-next v3] tcp: add a tracepoint for tcp retransmission

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Message-Id: <20171014.184528.1895579700537124041.davem@davemloft.net>
Date:   Sat, 14 Oct 2017 18:45:28 -0700 (PDT)
From:   David Miller <davem@...emloft.net>
To:     xiyou.wangcong@...il.com
Cc:     netdev@...r.kernel.org, edumazet@...gle.com,
        alexei.starovoitov@...il.com, hannes@...essinduktion.org,
        brendan.d.gregg@...il.com, ncardwell@...gle.com
Subject: Re: [Patch net-next v3] tcp: add a tracepoint for tcp
 retransmission

From: Cong Wang <xiyou.wangcong@...il.com>
Date: Fri, 13 Oct 2017 13:03:16 -0700

> We need a real-time notification for tcp retransmission
> for monitoring.
> 
> Of course we could use ftrace to dynamically instrument this
> kernel function too, however we can't retrieve the connection
> information at the same time, for example perf-tools [1] reads
> /proc/net/tcp for socket details, which is slow when we have
> a lots of connections.
> 
> Therefore, this patch adds a tracepoint for __tcp_retransmit_skb()
> and exposes src/dst IP addresses and ports of the connection.
> This also makes it easier to integrate into perf.
> 
> Note, I expose both IPv4 and IPv6 addresses at the same time:
> for a IPv4 socket, v4 mapped address is used as IPv6 addresses,
> for a IPv6 socket, LOOPBACK4_IPV6 is already filled by kernel.
> Also, add sk and skb pointers as they are useful for BPF.
> 
> 1. https://github.com/brendangregg/perf-tools/blob/master/net/tcpretrans
> 
> Cc: Eric Dumazet <edumazet@...gle.com>
> Cc: Alexei Starovoitov <alexei.starovoitov@...il.com>
> Cc: Hannes Frederic Sowa <hannes@...essinduktion.org>
> Cc: Brendan Gregg <brendan.d.gregg@...il.com>
> Cc: Neal Cardwell <ncardwell@...gle.com>
> Signed-off-by: Cong Wang <xiyou.wangcong@...il.com>

Applied, thank you.