From mboxrd@z Thu Jan  1 00:00:00 1970
From: Thomas Monjalon <thomas.monjalon@6wind.com>
Subject: Re: [PATCH v2] mbuf:rearrange mbuf to be more mbuf chain
	friendly
Date: Mon, 27 Jun 2016 11:05:09 +0200
Message-ID: <1706546.bAg9N1Gdxd@xps13>
References: <1466868582-66201-1-git-send-email-keith.wiles@intel.com>
 <2601191342CEEE43887BDE71AB97725836B7715C@irsmsx105.ger.corp.intel.com>
 <5770E365.4060703@6wind.com>
Mime-Version: 1.0
Content-Type: text/plain; charset="us-ascii"
Content-Transfer-Encoding: 7Bit
Cc: dev@dpdk.org, Olivier Matz <olivier.matz@6wind.com>, "Ananyev,
 Konstantin" <konstantin.ananyev@intel.com>
To: "Wiles, Keith" <keith.wiles@intel.com>
Return-path: <dev-bounces@dpdk.org>
Received: from mail-wm0-f51.google.com (mail-wm0-f51.google.com [74.125.82.51])
 by dpdk.org (Postfix) with ESMTP id C42155937
 for <dev@dpdk.org>; Mon, 27 Jun 2016 11:05:10 +0200 (CEST)
Received: by mail-wm0-f51.google.com with SMTP id r201so105051236wme.1
 for <dev@dpdk.org>; Mon, 27 Jun 2016 02:05:10 -0700 (PDT)
In-Reply-To: <5770E365.4060703@6wind.com>
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>
Errors-To: dev-bounces@dpdk.org
Sender: "dev" <dev-bounces@dpdk.org>

2016-06-27 10:27, Olivier Matz:
> On 06/27/2016 10:21 AM, Ananyev, Konstantin wrote:
> > From: dev [mailto:dev-bounces@dpdk.org] On Behalf Of Keith Wiles
> >> Move the next pointer to the first cacheline of the rte_mbuf structure
> >> and move the offload values to the second cacheline to give better
> >> performance to applications using chained mbufs.
> >>
> >> Enabled by a configuration option CONFIG_RTE_MBUF_CHAIN_FRIENDLY default
> >> is set to No.
> > 
> > First, it would make ixgbe and i40e vector RX functions to work incorrectly.
> > Second, I don't think we can afford to allow people swap mbuf fields in the way they like.
> > Otherwise we'll end-up with totally unmaintainable code pretty soon.
> > So NACK.  
> 
> +1

To be more precise, the arrangement of fields in rte_mbuf is open
to debate and changes.
There is a recent discussion here:
	http://dpdk.org/ml/archives/dev/2016-May/039483.html

I think we must try to improve few things in mbuf during the 16.11 cycle.
But it must not be allowed to have a build option to adapt this structure
or any other API. There is only one DPDK API for a given version.