From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mga03.intel.com (mga03.intel.com [134.134.136.65]) by dpdk.org (Postfix) with ESMTP id D837EB411 for ; Wed, 18 Feb 2015 11:37:56 +0100 (CET) Received: from fmsmga001.fm.intel.com ([10.253.24.23]) by orsmga103.jf.intel.com with ESMTP; 18 Feb 2015 02:31:48 -0800 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.09,600,1418112000"; d="scan'208";a="667994258" Received: from bricha3-mobl3.ger.corp.intel.com ([10.243.20.37]) by fmsmga001.fm.intel.com with SMTP; 18 Feb 2015 02:37:07 -0800 Received: by (sSMTP sendmail emulation); Wed, 18 Feb 2015 10:37:03 +0025 Date: Wed, 18 Feb 2015 10:37:03 +0000 From: Bruce Richardson To: Olivier MATZ Message-ID: <20150218103703.GB6804@bricha3-MOBL3> References: <1424102913-18944-1-git-send-email-sergio.gonzalez.monroy@intel.com> <1424102913-18944-3-git-send-email-sergio.gonzalez.monroy@intel.com> <54E45888.7070603@6wind.com> <20150218093548.GA14884@bricha3-MOBL3> <2601191342CEEE43887BDE71AB977258213EF5E4@irsmsx105.ger.corp.intel.com> <20150218100003.GA14728@bricha3-MOBL3> <54E46612.7050809@6wind.com> <20150218102253.GA6804@bricha3-MOBL3> <54E46A8C.9010105@6wind.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <54E46A8C.9010105@6wind.com> Organization: Intel Shannon Ltd. User-Agent: Mutt/1.5.23 (2014-03-12) Cc: "dev@dpdk.org" Subject: Re: [dpdk-dev] [PATCH 2/2] Remove RTE_MBUF_REFCNT references X-BeenThere: dev@dpdk.org X-Mailman-Version: 2.1.15 Precedence: list List-Id: patches and discussions about DPDK List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Wed, 18 Feb 2015 10:37:57 -0000 On Wed, Feb 18, 2015 at 11:33:48AM +0100, Olivier MATZ wrote: > Hi, > > On 02/18/2015 11:22 AM, Bruce Richardson wrote: > >On Wed, Feb 18, 2015 at 11:14:42AM +0100, Olivier MATZ wrote: > >>On 02/18/2015 11:00 AM, Bruce Richardson wrote: > >>>On Wed, Feb 18, 2015 at 09:48:58AM +0000, Ananyev, Konstantin wrote: > >>>>Hi lads, > >>>> > >>>>>-----Original Message----- > >>>>>From: dev [mailto:dev-bounces@dpdk.org] On Behalf Of Bruce Richardson > >>>>>Sent: Wednesday, February 18, 2015 9:36 AM > >>>>>To: Olivier MATZ > >>>>>Cc: dev@dpdk.org > >>>>>Subject: Re: [dpdk-dev] [PATCH 2/2] Remove RTE_MBUF_REFCNT references > >>>>> > >>>>>On Wed, Feb 18, 2015 at 10:16:56AM +0100, Olivier MATZ wrote: > >>>>>>Hi Sergio, > >>>>>> > >>>>>>On 02/16/2015 05:08 PM, Sergio Gonzalez Monroy wrote: > >>>>>>>This patch removes all references to RTE_MBUF_REFCNT, setting the refcnt > >>>>>>>field in the mbuf struct permanently. > >>>>>>> > >>>>>>>Signed-off-by: Sergio Gonzalez Monroy > >>>>>> > >>>>>>I think removing the refcount compile option goes in the right > >>>>>>direction. However, activating the refcount will break the applications > >>>>>>that reserve a private zone in mbufs. This is due to the macros > >>>>>>RTE_MBUF_TO_BADDR() and RTE_MBUF_FROM_BADDR() that suppose that > >>>>>>the beginning of the mbuf is 128 bytes (sizeof mbuf) before the > >>>>>>data buffer. > >>>>>> > >>>>> > >>>>>While I understand how the macros make certain assumptions, how does activating > >>>>>the refcnt specifically lead to the problems you describe? Could you explain > >>>>>that part in a bit more detail? > >>>>> > >>>>>Thanks, > >>>>>/Bruce > >>>>> > >>>> > >>>>Olivier, I also don't understand your concern here. > >>>>As I can see, that patch has nothing to do with RTE_MBUF_FROM_BADDR/ RTE_MBUF_FROM_BADDR macros. > >>>>They are still there, for example rte_pktmbuf_detach() still uses it to restore mbuf's buf_addr. > >>>>The only principal change here, is that we don't rely more on RTE_MBUF_FROM_BADDR to determine, > >>>>Is that indirect mbuf or not. > >>>>Instead we use a special falg for that purpose: > >>>> > >>>>-#define RTE_MBUF_INDIRECT(mb) (RTE_MBUF_FROM_BADDR((mb)->buf_addr) != (mb)) > >>>>+#define RTE_MBUF_INDIRECT(mb) (mb->ol_flags & IND_ATTACHED_MBUF) > >>>> > >>>>BTW, Sergio as I said before, I think it should be: > >>>>#define RTE_MBUF_INDIRECT(mb) ((mb)->ol_flags & IND_ATTACHED_MBUF) > >>>> > >>>>Konstantin > >>>> > >>>> > >>>>>>For RTE_MBUF_TO_BADDR(), it's relatively easy to replace it. The > >>>>>>mbuf pool could store the size of the private size like it's done > >>>>>>for mbp_priv->mbuf_data_room_size. Using rte_mempool_from_obj(m) > >>>>>>or m->pool, we can retrieve the mbuf pool and this value, then > >>>>>>compute the buffer address. > >>> > >>>Agreed, that makes sense. > >>> > >>>>>> > >>>>>>For RTE_MBUF_FROM_BADDR(), it's more complex. We could ensure that > >>>>>>a backpointer to the mbuf is always located before the data buffer, > >>>>>>but it looks difficult to do. > >>> > >>>On the other hand, with the proposed refcnt change Sergio proposes, we no > >>>longer use this macro in any of the built-in mbuf handling for freeing mbufs. > >>>Does this need to be solved at anything other than the application level? > >> > >>It's still used in __rte_pktmbuf_prefree_seg() to retrieve the > >>parent mbuf (direct) from the indirect mbuf beeing freed. > >> > >Yes, my bad. > >How was this managed before, since refcnt field seems to be necessary in order > >to effectively manage indirect mbufs? Is this just the case that this is something > >that never worked and that needs to be solved, or is it something that was > >working that this patch will now break? > > This is something that never worked before: refcounts are not compatible > with reserving private data in mbufs. This patch does not change the > issue, it is still there. > > Before the patch, an application that wanted to reserve a private > data could disable refcounts at compile-time. > After the patch, the solution is just to avoid using refcounts. > > Regards, > Olivier > Thanks for clarifying. So, you ok with this patch as a step in the right direction?