netdev - Re: [PATCH net-next] net: introduce a new tracepoint for tcp_rcv_space

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Date:   Mon, 16 Apr 2018 08:43:31 -0700
From:   Eric Dumazet <eric.dumazet@...il.com>
To:     Yafang Shao <laoar.shao@...il.com>, davem@...emloft.net
Cc:     kuznet@....inr.ac.ru, yoshfuji@...ux-ipv6.org,
        songliubraving@...com, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH net-next] net: introduce a new tracepoint for
 tcp_rcv_space_adjust



On 04/16/2018 08:33 AM, Yafang Shao wrote:
> tcp_rcv_space_adjust is called every time data is copied to user space,
> introducing a tcp tracepoint for which could show us when the packet is
> copied to user.
> This could help us figure out whether there's latency in user process.
> 
> When a tcp packet arrives, tcp_rcv_established() will be called and with
> the existed tracepoint tcp_probe we could get the time when this packet
> arrives.
> Then this packet will be copied to user, and tcp_rcv_space_adjust will
> be called and with this new introduced tracepoint we could get the time
> when this packet is copied to user.
> 
> 	arrives time : user process time    => latency caused by user
> 	tcp_probe      tcp_rcv_space_adjust
> 
> Hence in the prink message, sk is printed as a key to connect these two
> tracepoints.
> 

socket pointer is not a key.

TCP sockets can be reused pretty fast after free.

I suggest you go for cookie instead, this is an unique 64bit identifier.
( sock_gen_cookie() for details )