From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mga09.intel.com (mga09.intel.com [134.134.136.24]) by dpdk.org (Postfix) with ESMTP id B103B7EB0 for ; Thu, 4 Dec 2014 18:22:26 +0100 (CET) Received: from orsmga002.jf.intel.com ([10.7.209.21]) by orsmga102.jf.intel.com with ESMTP; 04 Dec 2014 09:21:09 -0800 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.07,517,1413270000"; d="scan'208";a="648353144" Received: from bricha3-mobl3.ger.corp.intel.com ([10.237.221.34]) by orsmga002.jf.intel.com with SMTP; 04 Dec 2014 09:22:15 -0800 Received: by (sSMTP sendmail emulation); Thu, 04 Dec 2014 17:22:14 +0025 Date: Thu, 4 Dec 2014 17:22:14 +0000 From: Bruce Richardson To: "Ananyev, Konstantin" Message-ID: <20141204172214.GC7732@bricha3-MOBL3> References: <1417703181-23093-1-git-send-email-jean-mickael.guerin@6wind.com> <20141204151500.GC9300@bricha3-MOBL3> <2601191342CEEE43887BDE71AB977258213BCA80@IRSMSX105.ger.corp.intel.com> <4349408.QROSJAq1DS@xps13> <2601191342CEEE43887BDE71AB977258213BCAE4@IRSMSX105.ger.corp.intel.com> <2601191342CEEE43887BDE71AB977258213BCB11@IRSMSX105.ger.corp.intel.com> <20141204165847.GA7732@bricha3-MOBL3> <2601191342CEEE43887BDE71AB977258213BCB91@IRSMSX105.ger.corp.intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <2601191342CEEE43887BDE71AB977258213BCB91@IRSMSX105.ger.corp.intel.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] ixgbe: don't override mbuf buffer length 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: Thu, 04 Dec 2014 17:22:28 -0000 On Thu, Dec 04, 2014 at 05:17:16PM +0000, Ananyev, Konstantin wrote: > > > > -----Original Message----- > > From: Richardson, Bruce > > Sent: Thursday, December 04, 2014 4:59 PM > > To: Ananyev, Konstantin > > Cc: Thomas Monjalon; dev@dpdk.org > > Subject: Re: [dpdk-dev] [PATCH 2/2] ixgbe: don't override mbuf buffer length > > > > On Thu, Dec 04, 2014 at 04:18:03PM +0000, Ananyev, Konstantin wrote: > > > > > > > > > > -----Original Message----- > > > > From: dev [mailto:dev-bounces@dpdk.org] On Behalf Of Ananyev, Konstantin > > > > Sent: Thursday, December 04, 2014 4:05 PM > > > > To: Thomas Monjalon > > > > Cc: dev@dpdk.org > > > > Subject: Re: [dpdk-dev] [PATCH 2/2] ixgbe: don't override mbuf buffer length > > > > > > > > > > > > > > > > > -----Original Message----- > > > > > From: Thomas Monjalon [mailto:thomas.monjalon@6wind.com] > > > > > Sent: Thursday, December 04, 2014 3:48 PM > > > > > To: Ananyev, Konstantin > > > > > Cc: dev@dpdk.org; Richardson, Bruce > > > > > Subject: Re: [dpdk-dev] [PATCH 2/2] ixgbe: don't override mbuf buffer length > > > > > > > > > > 2014-12-04 15:29, Ananyev, Konstantin: > > > > > > From: Richardson, Bruce > > > > > > > On Thu, Dec 04, 2014 at 02:50:11PM +0000, Ananyev, Konstantin wrote: > > > > > > > > From: dev [mailto:dev-bounces@dpdk.org] On Behalf Of Jean-Mickael Guerin > > > > > > > > > The template mbuf_initializer is hard coded with a buflen which > > > > > > > > > might have been set differently by the application at the time of > > > > > > > > > mbuf pool creation. > > > > > > > > > > > > > > > > > > Switch to a mbuf allocation, to fetch the correct default values. > > > > > > > > > There is no performance impact because this is not a data-plane API. > > > > > > > > > > > > > > > > > > Signed-off-by: Jean-Mickael Guerin > > > > > > > > > Acked-by: David Marchand > > > > > > > > > Fixes: 0ff3324da2 ("ixgbe: rework vector pmd following mbuf changes") > > > > > > > > > --- > > > > > > > > > lib/librte_pmd_ixgbe/ixgbe_rxtx_vec.c | 19 ++++++++++++------- > > > > > > > > > 1 file changed, 12 insertions(+), 7 deletions(-) > > > > > > > > > > > > > > > > > > diff --git a/lib/librte_pmd_ixgbe/ixgbe_rxtx_vec.c b/lib/librte_pmd_ixgbe/ixgbe_rxtx_vec.c > > > > > > > > > index c1b5a78..f7b02f5 100644 > > > > > > > > > --- a/lib/librte_pmd_ixgbe/ixgbe_rxtx_vec.c > > > > > > > > > +++ b/lib/librte_pmd_ixgbe/ixgbe_rxtx_vec.c > > > > > > > > > @@ -732,17 +732,22 @@ static struct ixgbe_txq_ops vec_txq_ops = { > > > > > > > > > int > > > > > > > > > ixgbe_rxq_vec_setup(struct igb_rx_queue *rxq) > > > > > > > > > { > > > > > > > > > - struct rte_mbuf mb_def = { .buf_addr = 0 }; /* zeroed mbuf */ > > > > > > > > > + struct rte_mbuf *mb_def; > > > > > > > > > > > > > > > > > > - mb_def.nb_segs = 1; > > > > > > > > > - mb_def.data_off = RTE_PKTMBUF_HEADROOM; > > > > > > > > > - mb_def.buf_len = rxq->mb_pool->elt_size - sizeof(struct rte_mbuf); > > > > > > > > > - mb_def.port = rxq->port_id; > > > > > > > > > - rte_mbuf_refcnt_set(&mb_def, 1); > > > > > > > > > + mb_def = rte_pktmbuf_alloc(rxq->mb_pool); > > > > > > > > > > > > > > > > Could you explain to me, what is an advantage of using dynamic allocation vs local struct here? > > > > > > > > I don't see any. > > > > > > > > > > > > > > It means that we get an mbuf that is initialized as done by the initialization > > > > > > > function passed to the mempool_create call. The static variable method assumes > > > > > > > that we configure the mbuf using default setting for buf_len etc. > > > > > > > > > > > > I understand that, but why it can't be done in some other way? > > > > > > Without allocating/freeing? > > > > > > Let say, at mempool_create() store obj_init() and then add ability to call it again? > > > > > > Anyway, it doesn't look to me like a critical problem, that requires an urgent patch for 1.8. > > > > > > > > > > Konstantin, when a bug is seen, it must be fixed ASAP. > > > > > > > > Well, it will be exposed only if someone will use a custom mbufs right? > > > > I.e, the se 2 lines would not be correct: > > > > mb_def.data_off = RTE_PKTMBUF_HEADROOM; > > > > mb_def.buf_len = rxq->mb_pool->elt_size - sizeof(struct rte_mbuf); > > > > > > > > Thoug we setup same data_off like that in all other PMDs as well. > > > > Something like that: > > > > m->data_off = RTE_PKTMBUF_HEADROOM; > > > > could be seen across all RX functions we have for different PMDs. > > > > > > > > The only difference is buf_len, but in theory even with dynamic allocation, > > > > the fix would be totally correct. > > > > As no one can guarantee, that with custom mbufs, all buffers inside the pool will have the same length. > > > > > > Which makes me think, that we probably shouldn't overwrite buf_len by rxq->mbuf_initializer. > > > > > I believe that it is perfectly safe to do so. All buffers from a mempool are meant > > to be the same size, therefore reading the length of one buffer should tell you > > what size all buffers are. > > Yes, objects in the mempool are the same size > But nothing prevents you, in your custom obj_init() to setup mbuf->buf_len to some other value, > that could be smaller, then mempool element size. > Let say you'd like all your mbufs from particular mempool to be at least 2K long and 1K aligned. > So you set RTE_MBUF_REFCNT_ATOMIC=n, and call rte_mempool_create(...,elst_size=0xc00,...); > Then at you custom obj_init() you do: > > struct rte_mbuf *m = RTE_ALIGN_CEIL(_m, 1024); > buf_len = mp->elt_size - sizeof(struct rte_mbuf) - (m - _m); > ... > > From my point, nothing wrong is done here, and we have a mempool where mbufs might have different buf_len. > > Another example, is attachment of external buffer to the mbuf. > We are doing it to support zero-copy inside our vhost app. > Right now we don't allow external buffer length be bigger then mbuf buf_len, but again some people may like to allow that. > Would the originally proposed solution not work in all these cases - assuming it's enhanced to catch and properly handle failure cases? > > If we do hit a scenario where we do need to support > > variable size buffers from a single mempool, we can do that via the older unoptimized > > code paths, I think, since it's a definite edge case. > > > > /Bruce >