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

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Date:   Fri, 18 Jan 2019 09:57:19 +0800
From:   Yafang Shao <laoar.shao@...il.com>
To:     Eric Dumazet <edumazet@...gle.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 Fri, Jan 18, 2019 at 12:40 AM Eric Dumazet <edumazet@...gle.com> wrote:
>
> 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>
>

Thanks for your correction.
Will change it and send v2.

>
> > 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
> >