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Date:   Tue, 17 Apr 2018 00:03:32 +0800
From:   Yafang Shao <>
To:     Eric Dumazet <>
Cc:     David Miller <>,
        Alexey Kuznetsov <>,, Song Liu <>,, LKML <>
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 <> 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.


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