netdev - Re: [PATCH net-next] net: sock: do not set sk_cookie in sk_clone

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Message-ID: <CANn89iJVBdB7mJh9PKyiBmDN3wsYkEy81Ag21dCXUGs3_D3=Qg@mail.gmail.com>
Date:   Thu, 17 Jan 2019 08:40:32 -0800
From:   Eric Dumazet <edumazet@...gle.com>
To:     Yafang Shao <laoar.shao@...il.com>
Cc:     David Miller <davem@...emloft.net>,
        netdev <netdev@...r.kernel.org>, shaoyafang@...iglobal.com
Subject: Re: [PATCH net-next] net: sock: do not set sk_cookie in sk_clone_lock()

On Thu, Jan 17, 2019 at 2:02 AM Yafang Shao <laoar.shao@...il.com> wrote:
>
> The only call site of sk_clone_lock is in inet_csk_clone_lock,
> and sk_cookie will be set there.
> So we don't need to set sk_cookie in sk_clone_lock().
> That can save an atomic operation.
>

Patch is fine, although the wording of ' atomic operation'  is a bit misleading.

atomic_set or atomic_read are plain memory writes and reads.

Real ' atomic and expensive'  operations are the ones doing RMW
operations (with lock semantic on SMP)

Reviewed-by: Eric Dumazet <edumazet@...gle.com>


> Signed-off-by: Yafang Shao <laoar.shao@...il.com>
> ---
>  net/core/sock.c | 1 -
>  1 file changed, 1 deletion(-)
>
> diff --git a/net/core/sock.c b/net/core/sock.c
> index f00902c..21e2a84 100644
> --- a/net/core/sock.c
> +++ b/net/core/sock.c
> @@ -1726,7 +1726,6 @@ struct sock *sk_clone_lock(const struct sock *sk, const gfp_t priority)
>                 newsk->sk_err_soft = 0;
>                 newsk->sk_priority = 0;
>                 newsk->sk_incoming_cpu = raw_smp_processor_id();
> -               atomic64_set(&newsk->sk_cookie, 0);
>                 if (likely(newsk->sk_net_refcnt))
>                         sock_inuse_add(sock_net(newsk), 1);
>
> --
> 1.8.3.1
>