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

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Message-ID: <CALOAHbB98bXsMAggQi0p0Mgu=Rp4Kot+JzPQ+sRvubFG=Yyt=A@mail.gmail.com>
Date:   Tue, 17 Apr 2018 00:03:32 +0800
From:   Yafang Shao <laoar.shao@...il.com>
To:     Eric Dumazet <eric.dumazet@...il.com>
Cc:     David Miller <davem@...emloft.net>,
        Alexey Kuznetsov <kuznet@....inr.ac.ru>,
        yoshfuji@...ux-ipv6.org, Song Liu <songliubraving@...com>,
        netdev@...r.kernel.org, LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH net-next] net: introduce a new tracepoint for tcp_rcv_space_adjust

On Mon, Apr 16, 2018 at 11:43 PM, Eric Dumazet <eric.dumazet@...il.com> wrote:
>
>
> 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 )
>
>

Thanks for your explanation.
Will have a try.

Thanks
Yafang