From mboxrd@z Thu Jan  1 00:00:00 1970
From: Jerin Jacob <jerin.jacob@caviumnetworks.com>
Subject: Re: [PATCH v4 2/4] ring: read tail using atomic load
Date: Thu, 20 Sep 2018 06:41:26 +0000
Message-ID: <20180920064117.GC2283@jerin>
References: <20180917074735.28161-1-gavin.hu@arm.com>
 <1537171879-64390-1-git-send-email-gavin.hu@arm.com>
 <1537171879-64390-2-git-send-email-gavin.hu@arm.com>
Mime-Version: 1.0
Content-Type: text/plain; charset="us-ascii"
Content-Transfer-Encoding: quoted-printable
Cc: "dev@dpdk.org" <dev@dpdk.org>, "Honnappa.Nagarahalli@arm.com"
 <Honnappa.Nagarahalli@arm.com>, "steve.capper@arm.com"
 <steve.capper@arm.com>, "Ola.Liljedahl@arm.com" <Ola.Liljedahl@arm.com>,
 "nd@arm.com" <nd@arm.com>, "stable@dpdk.org" <stable@dpdk.org>,
 "jia.he@hxt-semitech.com" <jia.he@hxt-semitech.com>
To: Gavin Hu <gavin.hu@arm.com>
Return-path: <dev-bounces@dpdk.org>
In-Reply-To: <1537171879-64390-2-git-send-email-gavin.hu@arm.com>
Content-Language: en-US
Content-ID: <3438533554E3414CA6CE7B017B522717@namprd07.prod.outlook.com>
List-Id: DPDK patches and discussions <dev.dpdk.org>
List-Unsubscribe: <https://mails.dpdk.org/options/dev>,
 <mailto:dev-request@dpdk.org?subject=unsubscribe>
List-Archive: <http://mails.dpdk.org/archives/dev/>
List-Post: <mailto:dev@dpdk.org>
List-Help: <mailto:dev-request@dpdk.org?subject=help>
List-Subscribe: <https://mails.dpdk.org/listinfo/dev>,
 <mailto:dev-request@dpdk.org?subject=subscribe>
Errors-To: dev-bounces@dpdk.org
Sender: "dev" <dev-bounces@dpdk.org>

-----Original Message-----
> Date: Mon, 17 Sep 2018 16:11:17 +0800
> From: Gavin Hu <gavin.hu@arm.com>
> To: dev@dpdk.org
> CC: gavin.hu@arm.com, Honnappa.Nagarahalli@arm.com, steve.capper@arm.com,
>  Ola.Liljedahl@arm.com, jerin.jacob@caviumnetworks.com, nd@arm.com,
>  stable@dpdk.org
> Subject: [PATCH v4 2/4] ring: read tail using atomic load
> X-Mailer: git-send-email 2.7.4
>=20
>=20
> In update_tail, read ht->tail using __atomic_load.Although the
> compiler currently seems to be doing the right thing even without
> _atomic_load, we don't want to give the compiler freedom to optimise
> what should be an atomic load, it should not be arbitarily moved
> around.
>=20
> Fixes: 39368ebfc6 ("ring: introduce C11 memory model barrier option")
> Cc: stable@dpdk.org


+ Jia He <jia.he@hxt-semitech.com>

>=20
> Signed-off-by: Gavin Hu <gavin.hu@arm.com>
> Reviewed-by: Honnappa Nagarahalli <Honnappa.Nagarahalli@arm.com>
> Reviewed-by: Steve Capper <steve.capper@arm.com>
> Reviewed-by: Ola Liljedahl <Ola.Liljedahl@arm.com>
> ---
>  lib/librte_ring/rte_ring_c11_mem.h | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
>=20
> diff --git a/lib/librte_ring/rte_ring_c11_mem.h b/lib/librte_ring/rte_rin=
g_c11_mem.h
> index 94df3c4..234fea0 100644
> --- a/lib/librte_ring/rte_ring_c11_mem.h
> +++ b/lib/librte_ring/rte_ring_c11_mem.h
> @@ -21,7 +21,8 @@ update_tail(struct rte_ring_headtail *ht, uint32_t old_=
val, uint32_t new_val,
>          * we need to wait for them to complete
>          */
>         if (!single)
> -               while (unlikely(ht->tail !=3D old_val))
> +               while (unlikely(old_val !=3D __atomic_load_n(&ht->tail,
> +                                               __ATOMIC_RELAXED)))
>                         rte_pause();
>=20
>         __atomic_store_n(&ht->tail, new_val, __ATOMIC_RELEASE);
> --
> 2.7.4
>=20