netdev - Re: [PATCH] RDS: Simplify code

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Message-ID: <20160905051422.GT21847@leon.nu>
Date:   Mon, 5 Sep 2016 08:14:22 +0300
From:   Leon Romanovsky <leon@...nel.org>
To:     Christophe JAILLET <christophe.jaillet@...adoo.fr>
Cc:     linux-rdma@...r.kernel.org, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org, kernel-janitors@...r.kernel.org
Subject: Re: [PATCH] RDS: Simplify code

On Mon, Sep 05, 2016 at 06:38:21AM +0200, Christophe JAILLET wrote:
> Le 04/09/2016 à 20:23, Leon Romanovsky a écrit :
> >On Sun, Sep 04, 2016 at 05:57:20PM +0200, Christophe JAILLET wrote:
> >>Le 04/09/2016 à 14:20, Leon Romanovsky a écrit :
> >>>On Sat, Sep 03, 2016 at 07:33:29AM +0200, Christophe JAILLET wrote:
> >>>>Calling 'list_splice' followed by 'INIT_LIST_HEAD' is equivalent to
> >>>>'list_splice_init'.
> >>>It is not 100% accurate
> >>>
> >>>list_splice(y, z)
> >>>INIT_LIST_HEAD(y)
> >>>
> >>>==>
> >>>
> >>>if (!list_empty(y))
> >>>      __list_splice(y, z, z>next);
> >>>INIT_LIST_HEAD(y)
> >>>
> >>>and not
> >>>
> >>>if (!list_empty(y)) {
> >>>      __list_splice(y, z, z>next);
> >>>      INIT_LIST_HEAD(y)
> >>>}
> >>>
> >>>as list_splice_init will do.
> >>>
> >>You are right but if you dig further you will see that calling
> >>INIT_LIST_HEAD on an empty list is a no-op (AFAIK).
> >>And if this list was not already correctly initialized, then you would have
> >>some other troubles.
> >Thank you for the suggestion,
> >It looks like the code after that can be skipped in case of loop_conns
> >list is empty, the tmp_list will be empty too.
> >
> >174         list_for_each_entry_safe(lc, _lc, &tmp_list, loop_node) {
> >175                 WARN_ON(lc->conn->c_passive);
> >176                 rds_conn_destroy(lc->conn);
> >177         }
> Yes, but this would require some more code and test. This function doesn't
> seem to be in a hot path, so I'm not sure that the added complexity would
> worth it.
> It would require a new 'list_empty()' test and some code rearrangement.
>
> I suppose that testing for emptiness at the beginning or going through a
> list_for_each_entry_safe on a empty list (which will exit immediately and do
> nothing) is more or less the same in term of speed. So keep the code simple
> and readable.

I would expect one list_empty check at the beginning and return
immediately, but anyway it doesn't matter.

>
> CJ
>
>
> --
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