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 92DAE5A51 for ; Sun, 13 Sep 2015 17:54:28 +0200 (CEST) Received: from fmsmga003.fm.intel.com ([10.253.24.29]) by orsmga102.jf.intel.com with ESMTP; 13 Sep 2015 08:54:27 -0700 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.17,523,1437462000"; d="scan'208";a="560895360" Received: from irsmsx106.ger.corp.intel.com ([163.33.3.31]) by FMSMGA003.fm.intel.com with ESMTP; 13 Sep 2015 08:54:25 -0700 Received: from irsmsx155.ger.corp.intel.com (163.33.192.3) by IRSMSX106.ger.corp.intel.com (163.33.3.31) with Microsoft SMTP Server (TLS) id 14.3.224.2; Sun, 13 Sep 2015 16:54:24 +0100 Received: from irsmsx105.ger.corp.intel.com ([169.254.7.51]) by irsmsx155.ger.corp.intel.com ([169.254.14.184]) with mapi id 14.03.0224.002; Sun, 13 Sep 2015 16:54:24 +0100 From: "Ananyev, Konstantin" To: Avi Kivity , Thomas Monjalon , Vladislav Zolotarov , didier.pallard Thread-Topic: [dpdk-dev] [PATCH v1] ixgbe_pmd: forbid tx_rs_thresh above 1 for all NICs but 82598 Thread-Index: AQHQ7Lod8WXH6ER9q0eam+oVD21uiZ46T9HAgAAGiYCAAEcqcA== Date: Sun, 13 Sep 2015 15:54:24 +0000 Message-ID: <2601191342CEEE43887BDE71AB97725836A85FDD@irsmsx105.ger.corp.intel.com> References: <1439489195-31553-1-git-send-email-vladz@cloudius-systems.com> <55F2F6A9.6080405@cloudius-systems.com> <3734976.j9Azrvq6io@xps13> <55F313E4.2080300@cloudius-systems.com> <2601191342CEEE43887BDE71AB97725836A85E36@irsmsx105.ger.corp.intel.com> <55F56CEB.6060808@cloudius-systems.com> In-Reply-To: <55F56CEB.6060808@cloudius-systems.com> Accept-Language: en-IE, en-US Content-Language: en-US X-MS-Has-Attach: X-MS-TNEF-Correlator: x-originating-ip: [163.33.239.180] Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: quoted-printable MIME-Version: 1.0 Cc: "dev@dpdk.org" Subject: Re: [dpdk-dev] [PATCH v1] ixgbe_pmd: forbid tx_rs_thresh above 1 for all NICs but 82598 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: Sun, 13 Sep 2015 15:54:29 -0000 > -----Original Message----- > From: Avi Kivity [mailto:avi@cloudius-systems.com] > Sent: Sunday, September 13, 2015 1:33 PM > To: Ananyev, Konstantin; Thomas Monjalon; Vladislav Zolotarov; didier.pal= lard > Cc: dev@dpdk.org > Subject: Re: [dpdk-dev] [PATCH v1] ixgbe_pmd: forbid tx_rs_thresh above 1= for all NICs but 82598 >=20 > On 09/13/2015 02:47 PM, Ananyev, Konstantin wrote: > > > >> -----Original Message----- > >> From: dev [mailto:dev-bounces@dpdk.org] On Behalf Of Avi Kivity > >> Sent: Friday, September 11, 2015 6:48 PM > >> To: Thomas Monjalon; Vladislav Zolotarov; didier.pallard > >> Cc: dev@dpdk.org > >> Subject: Re: [dpdk-dev] [PATCH v1] ixgbe_pmd: forbid tx_rs_thresh abov= e 1 for all NICs but 82598 > >> > >> On 09/11/2015 07:08 PM, Thomas Monjalon wrote: > >>> 2015-09-11 18:43, Avi Kivity: > >>>> On 09/11/2015 06:12 PM, Vladislav Zolotarov wrote: > >>>>> On Sep 11, 2015 5:55 PM, "Thomas Monjalon" >>>>> > wrote: > >>>>>> 2015-09-11 17:47, Avi Kivity: > >>>>>>> On 09/11/2015 05:25 PM, didier.pallard wrote: > >>>>>>>> Hi vlad, > >>>>>>>> > >>>>>>>> Documentation states that a packet (or multiple packets in trans= mit > >>>>>>>> segmentation) can span any number of > >>>>>>>> buffers (and their descriptors) up to a limit of 40 minus WTHRES= H > >>>>>>>> minus 2. > >>>>>>>> > >>>>>>>> Shouldn't there be a test in transmit function that drops > >>>>> properly the > >>>>>>>> mbufs with a too large number of > >>>>>>>> segments, while incrementing a statistic; otherwise transmit > >>>>> function > >>>>>>>> may be locked by the faulty packet without > >>>>>>>> notification. > >>>>>>>> > >>>>>>> What we proposed is that the pmd expose to dpdk, and dpdk expose > >>>>> to the > >>>>>>> application, an mbuf check function. This way applications that = can > >>>>>>> generate complex packets can verify that the device will be able = to > >>>>>>> process them, and applications that only generate simple mbufs ca= n > >>>>> avoid > >>>>>>> the overhead by not calling the function. > >>>>>> More than a check, it should be exposed as a capability of the por= t. > >>>>>> Anyway, if the application sends too much segments, the driver mus= t > >>>>>> drop it to avoid hang, and maintain a dedicated statistic counter = to > >>>>>> allow easy debugging. > >>>>> I agree with Thomas - this should not be optional. Malformed packet= s > >>>>> should be dropped. In the icgbe case it's a very simple test - it's= a > >>>>> single branch per packet so i doubt that it could impose any > >>>>> measurable performance degradation. > >>>> A drop allows the application no chance to recover. The driver must > >>>> either provide the ability for the application to know that it canno= t > >>>> accept the packet, or it must fix it up itself. > >>> I have the feeling that everybody agrees on the same thing: > >>> the application must be able to make a well formed packet by checking > >>> limitations of the port. What about a field rte_eth_dev_info.max_tx_s= egs? > >> It is not generic enough. i40e has a limit that it imposes post-TSO. > >> > >> > >>> In case the application fails in its checks, the driver must drop it = and > >>> notify the user via a stat counter. > >>> The driver can also remove the hardware limitation by gathering the s= egments > >>> but it may be hard to implement and would be a slow operation. > >> I think that to satisfy both the 64b full line rate applications and t= he > >> more complicated full stack applications, this must be made optional. > >> In particular, and application that only forwards packets will never h= it > >> a NIC's limits, so it need not take any action. That's why I think a > >> verification function is ideal; a forwarding application can ignore it= , > >> and a complex application can call it, and if it fails the packet, it > >> can linearize it itself, removing complexity from dpdk itself. > > I think that's a good approach to that problem. > > As I remember we discussed something similar a while ago - > > A function (tx_prep() or something) that would check nb_segs and probab= ly some other HW specific restrictions, > > calculate pseudo-header checksum, reset ip header len, etc. > > > > From other hand we also can add two more fields into rte_eth_dev_info: > > 1) Max num of segs per TSO packet (tx_max_seg ?). > > 2) Max num of segs per single packet/TSO segment (tx_max_mtu_seg ?). > > So for ixgbe both will have value 40 - wthresh, > > while for i40e 1) would be UINT8_MAX and 2) will be 8. > > Then upper layer can use that information to select an optimal size for= its TX buffers. > > > > >=20 > This will break whenever the fevered imagination of hardware designers > comes up with a new limit. >=20 > We can have an internal function that accepts these two parameters, and > then the driver-specific function can call this internal function: >=20 > static bool i40e_validate_packet(mbuf* m) { > return rte_generic_validate_packet(m, 0, 8); > } >=20 > static bool ixgbe_validate_packet(mbuf* m) { > return rte_generic_validate_packet(m, 40, 2); > } >=20 > this way, the application is isolated from changes in how invalid > packets are detected. >=20 >=20 I am not saying we shouldn't have tx_prep (tx_validate?) function per PMD. As I said before I like that approach. I think we should have tx_prep (as you suggested) that most people using fu= ll-path TX would call, *plus* these extra fields in re_eth_dev_conf, so if someone needs that info= rmation - it would be there.=20 Konstantin