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Subject: Re: [PATCH net-next] net: init sk_cookie for inet socket
To:     Yafang Shao <laoar.shao@gmail.com>
Cc:     David Miller <davem@davemloft.net>,
        Alexei Starovoitov <alexei.starovoitov@gmail.com>,
        netdev@vger.kernel.org, LKML <linux-kernel@vger.kernel.org>
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From:   Eric Dumazet <eric.dumazet@gmail.com>
Message-ID: <45bfd7ce-ecfa-8a4d-b1ed-8914a6b90093@gmail.com>
Date:   Tue, 24 Apr 2018 05:37:13 -0700
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On 04/24/2018 04:47 AM, Yafang Shao wrote:

> 
> Could you pls. explain the issue to me ?

Just run a synflood test on your host, it will definitely show the atomic
consuming most cpu cycles in inet_reqsk_alloc(), because of huge contention
on a cache line shared by all cpus.

Performance is reduced from ~5 Mpps to ~3.8 Mpps with 16 RX queues on my host.

atomic64_inc_return(&sock_net(sk)->cookie_gen) was not meant to be used in the
normal case (when a socket cookie is not ever requested/needed)