From mboxrd@z Thu Jan  1 00:00:00 1970
Return-Path: <dev-bounces@dpdk.org>
Received: from dpdk.org (dpdk.org [92.243.14.124])
	by inbox.dpdk.org (Postfix) with ESMTP id 57E72A00E6
	for <public@inbox.dpdk.org>; Thu, 11 Jul 2019 09:36:42 +0200 (CEST)
Received: from [92.243.14.124] (localhost [127.0.0.1])
	by dpdk.org (Postfix) with ESMTP id 35D7A397D;
	Thu, 11 Jul 2019 09:36:41 +0200 (CEST)
Received: from proxy.6wind.com (host.76.145.23.62.rev.coltfrance.com
 [62.23.145.76]) by dpdk.org (Postfix) with ESMTP id 1B0C83772
 for <dev@dpdk.org>; Thu, 11 Jul 2019 09:36:40 +0200 (CEST)
Received: from core.dev.6wind.com (unknown [10.0.0.1])
 by proxy.6wind.com (Postfix) with ESMTPS id EDDEF2E51A2;
 Thu, 11 Jul 2019 09:36:39 +0200 (CEST)
Received: from [10.16.0.195] (helo=6wind.com)
 by core.dev.6wind.com with smtp (Exim 4.84_2)
 (envelope-from <olivier.matz@6wind.com>)
 id 1hlTd8-0002am-TT; Thu, 11 Jul 2019 09:36:39 +0200
Received: by 6wind.com (sSMTP sendmail emulation);
 Thu, 11 Jul 2019 09:36:38 +0200
Date: Thu, 11 Jul 2019 09:36:38 +0200
From: Olivier Matz <olivier.matz@6wind.com>
To: Stephen Hemminger <stephen@networkplumber.org>
Cc: dev@dpdk.org
Message-ID: <20190711073638.64ljp526pengnwga@glumotte.dev.6wind.com>
References: <20190710092907.5565-1-olivier.matz@6wind.com>
 <20190710104917.73bc9201@hermes.lan>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <20190710104917.73bc9201@hermes.lan>
User-Agent: NeoMutt/20170113 (1.7.2)
Subject: Re: [dpdk-dev] [RFC] mbuf: support dynamic fields and flags
X-BeenThere: dev@dpdk.org
X-Mailman-Version: 2.1.15
Precedence: list
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>

On Wed, Jul 10, 2019 at 10:49:17AM -0700, Stephen Hemminger wrote:
> On Wed, 10 Jul 2019 11:29:07 +0200
> Olivier Matz <olivier.matz@6wind.com> wrote:
> 
> >  /**
> >   * Indicate that the metadata field in the mbuf is in use.
> > @@ -738,6 +741,8 @@ struct rte_mbuf {
> >  	 */
> >  	struct rte_mbuf_ext_shared_info *shinfo;
> >  
> > +	uint64_t dynfield1; /**< Reserved for dynamic fields. */
> > +	uint64_t dynfield2; /**< Reserved for dynamic fields. */
> >  } __rte_cache_aligned;
> 
> Growing mbuf is a fundamental ABI break and this needs
> higher level approval.

The size of the mbuf is still 128, I used the last 16 bytes that
were unused.

Later, we can think about removing existing fields and replace
them by a dynfield area, which can be anywhere in the structure
(even if it is in a 1 byte hole).

>  Why not one pointer?

A pointer to what?

> It looks like you are creating something like FreeBSD m_tag.
> Why not use that?

My implementation targets performance (accessing to *(mbuf + offset)
should be nearly as fast as accessing to a static field), at the price
of less flexibility compared to something like FreeBSD m_tag.