From mboxrd@z Thu Jan  1 00:00:00 1970
Return-Path: <bruce.richardson@intel.com>
Received: from mga14.intel.com (mga14.intel.com [192.55.52.115])
 by dpdk.org (Postfix) with ESMTP id CBCD12A66
 for <dev@dpdk.org>; Tue,  5 Jul 2016 11:47:35 +0200 (CEST)
Received: from fmsmga001.fm.intel.com ([10.253.24.23])
 by fmsmga103.fm.intel.com with ESMTP; 05 Jul 2016 02:47:34 -0700
X-ExtLoop1: 1
X-IronPort-AV: E=Sophos;i="5.26,579,1459839600"; d="scan'208";a="1001144032"
Received: from bricha3-mobl3.ger.corp.intel.com ([10.237.220.53])
 by fmsmga001.fm.intel.com with SMTP; 05 Jul 2016 02:47:32 -0700
Received: by  (sSMTP sendmail emulation); Tue, 05 Jul 2016 10:47:32 +0025
Date: Tue, 5 Jul 2016 10:47:32 +0100
From: Bruce Richardson <bruce.richardson@intel.com>
To: Wang Xiao W <xiao.w.wang@intel.com>
Cc: jing.d.chen@intel.com, dev@dpdk.org
Message-ID: <20160705094731.GE10232@bricha3-MOBL3>
References: <1467618668-28611-1-git-send-email-xiao.w.wang@intel.com>
 <20160705094342.GD10232@bricha3-MOBL3>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <20160705094342.GD10232@bricha3-MOBL3>
Organization: Intel Research and =?iso-8859-1?Q?De=ACvel?=
 =?iso-8859-1?Q?opment?= Ireland Ltd.
User-Agent: Mutt/1.5.23 (2014-03-12)
Subject: Re: [dpdk-dev] [PATCH] net/fm10k: fix Rx descriptor read timing
X-BeenThere: dev@dpdk.org
X-Mailman-Version: 2.1.15
Precedence: list
List-Id: patches and discussions about DPDK <dev.dpdk.org>
List-Unsubscribe: <http://dpdk.org/ml/options/dev>,
 <mailto:dev-request@dpdk.org?subject=unsubscribe>
List-Archive: <http://dpdk.org/ml/archives/dev/>
List-Post: <mailto:dev@dpdk.org>
List-Help: <mailto:dev-request@dpdk.org?subject=help>
List-Subscribe: <http://dpdk.org/ml/listinfo/dev>,
 <mailto:dev-request@dpdk.org?subject=subscribe>
X-List-Received-Date: Tue, 05 Jul 2016 09:47:36 -0000

On Tue, Jul 05, 2016 at 10:43:42AM +0100, Bruce Richardson wrote:
> On Mon, Jul 04, 2016 at 03:51:08PM +0800, Wang Xiao W wrote:
> > We find that when traffic is light, a few amount of packets will be
> > wrongly parsed (e.g. packet type), however this issue will not happen
> > when traffic is heavy.
> > 
> > The root cause is some fields in fm10k_rx_desc are read at wrong timing.
> > When the input speed is slower than software's capability, fm10k scalar
> > Rx function accesses descriptors closely to HW, so there's potential
> > sequence: some fields like pkt_info in fm10k_rx_desc are read before HW
> > writeback but some fields like DD bit are read after HW writeback, this
> > will lead to the later packet parsing function using incorrect value.
> > 
> > This patch fixes this issue by reading and parsing Rx descriptor after
> > DD bit is set.
> > 
> > Fixes: 4b61d3bfa941 ("fm10k: add receive and tranmit")
> > Fixes: c82dd0a7bfa5 ("fm10k: add scatter receive")
> > 
> > Signed-off-by: Wang Xiao W <xiao.w.wang@intel.com>
> 
> Fix looks correct to me. The key part I think is that the read of the
> descriptor at line "desc = q->hw_ring[next_dd];" is not atomic as it's
> a read of 16B, allowing part of the descriptor to be read either side of
> a HW write-back.
> 
> Acked-by: Bruce Richardson <bruce.richardson@intel.com>
> 
Applied to dpdk-next-net/rel_16_07

/Bruce