From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mga11.intel.com (mga11.intel.com [192.55.52.93]) by dpdk.org (Postfix) with ESMTP id DDAF71023 for ; Tue, 24 Jan 2017 02:43:09 +0100 (CET) Received: from fmsmga001.fm.intel.com ([10.253.24.23]) by fmsmga102.fm.intel.com with ESMTP; 23 Jan 2017 17:43:08 -0800 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.33,276,1477983600"; d="scan'208";a="1098007880" Received: from irsmsx102.ger.corp.intel.com ([163.33.3.155]) by fmsmga001.fm.intel.com with ESMTP; 23 Jan 2017 17:43:07 -0800 Received: from irsmsx105.ger.corp.intel.com ([169.254.7.38]) by IRSMSX102.ger.corp.intel.com ([169.254.2.230]) with mapi id 14.03.0248.002; Tue, 24 Jan 2017 01:43:06 +0000 From: "Ananyev, Konstantin" To: "Wiles, Keith" , Stephen Hemminger CC: "Hu, Jiayu" , "dev@dpdk.org" , "Kinsella, Ray" , "Gilmore, Walter E" , "Venkatesan, Venky" , "yuanhan.liu@linux.intel.com" Thread-Topic: [dpdk-dev] [RFC] Add GRO support in DPDK Thread-Index: AQHSdXke8G3CoYE5S0ao0Pji4hqADqFGTb0AgABNfoCAAD8VoA== Date: Tue, 24 Jan 2017 01:43:06 +0000 Message-ID: <2601191342CEEE43887BDE71AB9772583F10AD94@irsmsx105.ger.corp.intel.com> References: <1485176592-111525-1-git-send-email-jiayu.hu@intel.com> <20170123091550.212dca35@xeon-e3> <6B5C6BED-CAD4-4C51-8FB7-8509663B813B@intel.com> In-Reply-To: <6B5C6BED-CAD4-4C51-8FB7-8509663B813B@intel.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 Subject: Re: [dpdk-dev] [RFC] Add GRO support in DPDK X-BeenThere: dev@dpdk.org X-Mailman-Version: 2.1.15 Precedence: list List-Id: DPDK patches and discussions List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Tue, 24 Jan 2017 01:43:10 -0000 > -----Original Message----- > From: Wiles, Keith > Sent: Monday, January 23, 2017 9:53 PM > To: Stephen Hemminger > Cc: Hu, Jiayu ; dev@dpdk.org; Kinsella, Ray ; Ananyev, Konstantin > ; Gilmore, Walter E ; Venkatesan, Venky ; > yuanhan.liu@linux.intel.com > Subject: Re: [dpdk-dev] [RFC] Add GRO support in DPDK >=20 >=20 > > On Jan 23, 2017, at 10:15 AM, Stephen Hemminger wrote: > > > > On Mon, 23 Jan 2017 21:03:12 +0800 > > Jiayu Hu wrote: > > > >> With the support of hardware segmentation techniques in DPDK, the > >> networking stack overheads of send-side of applications, which directl= y > >> leverage DPDK, have been greatly reduced. But for receive-side, number= s of > >> segmented packets seriously burden the networking stack of application= s. > >> Generic Receive Offload (GRO) is a widely used method to solve the > >> receive-side issue, which gains performance by reducing the amount of > >> packets processed by the networking stack. But currently, DPDK doesn't > >> support GRO. Therefore, we propose to add GRO support in DPDK, and thi= s > >> RFC is used to explain the basic DPDK GRO design. > >> > >> DPDK GRO is a SW-based packets assembly library, which provides GRO > >> abilities for numbers of protocols. In DPDK GRO, packets are merged > >> before returning to applications and after receiving from drivers. > >> > >> In DPDK, GRO is a capability of NIC drivers. That support GRO or not a= nd > >> what GRO types are supported are up to NIC drivers. Different drivers = may > >> support different GRO types. By default, drivers enable all supported = GRO > >> types. For applications, they can inquire the supported GRO types by > >> each driver, and can control what GRO types are applied. For example, > >> ixgbe supports TCP and UDP GRO, but the application just needs TCP GRO= . > >> The application can disable ixgbe UDP GRO. > >> > >> To support GRO, a driver should provide a way to tell applications wha= t > >> GRO types are supported, and provides a GRO function, which is in char= ge > >> of assembling packets. Since different drivers may support different G= RO > >> types, their GRO functions may be different. For applications, they do= n't > >> need extra operations to enable GRO. But if there are some GRO types t= hat > >> are not needed, applications can use an API, like > >> rte_eth_gro_disable_protocols, to disable them. Besides, they can > >> re-enable the disabled ones. > >> > >> The GRO function processes numbers of packets at a time. In each > >> invocation, what GRO types are applied depends on applications, and th= e > >> amount of packets to merge depends on the networking status and > >> applications. Specifically, applications determine the maximum number = of > >> packets to be processed by the GRO function, but how many packets are > >> actually processed depends on if there are available packets to receiv= e. > >> For example, the receive-side application asks the GRO function to > >> process 64 packets, but the sender only sends 40 packets. At this time= , > >> the GRO function returns after processing 40 packets. To reassemble th= e > >> given packets, the GRO function performs an "assembly procedure" on ea= ch > >> packet. We use an example to demonstrate this procedure. Supposing the > >> GRO function is going to process packetX, it will do the following two > >> things: > >> a. Find a L4 assembly function according to the packet type of > >> packetX. A L4 assembly function is in charge of merging packets of a > >> specific type. For example, TCPv4 assembly function merges packets > >> whose L3 IPv4 and L4 is TCP. Each L4 assembly function has a packet > >> array, which keeps the packets that are unable to assemble. > >> Initially, the packet array is empty; > >> b. The L4 assembly function traverses own packet array to find a > >> mergeable packet (comparing Ethernet, IP and L4 header fields). If > >> finds, merges it and packetX via chaining them together; if doesn't, > >> allocates a new array element to store packetX and updates element > >> number of the array. > >> After performing the assembly procedure to all packets, the GRO functi= on > >> combines the results of all packet arrays, and returns these packets t= o > >> applications. > >> > >> There are lots of ways to implement the above design in DPDK. One of t= he > >> ways is: > >> a. Drivers tell applications what GRO types are supported via > >> dev->dev_ops->dev_infos_get; > >> b. When initialize, drivers register own GRO function as a RX > >> callback, which is invoked inside rte_eth_rx_burst. The name of the > >> GRO function should be like xxx_gro_receive (e.g. ixgbe_gro_receive). > >> Currently, the RX callback can only process the packets returned by > >> dev->rx_pkt_burst each time, and the maximum packet number > >> dev->rx_pkt_burst returns is determined by each driver, which can't > >> be interfered by applications. Therefore, to implement the above GRO > >> design, we have to modify current RX implementation to make driver > >> return packets as many as possible until the packet number meets the > >> demand of applications or there are not available packets to receive. > >> This modification is also proposed in patch: > >> http://dpdk.org/ml/archives/dev/2017-January/055887.html; > >> c. The GRO types to apply and the maximum number of packets to merge > >> are passed by resetting RX callback parameters. It can be achieved by > >> invoking rte_eth_rx_callback; > >> d. Simply, we can just store packet addresses into the packet array. > >> To check one element, we need to fetch the packet via its address. > >> However, this simple design is not efficient enough. Since whenever > >> checking one packet, one pointer dereference is generated. And a > >> pointer dereference always causes a cache line miss. A better way is > >> to store some rules in each array element. The rules must be the > >> prerequisites of merging two packets, like the sequence number of TCP > >> packets. We first compare the rules, then retrieve the packet if the > >> rules match. If storing the rules causes the packet array structure > >> is cache-unfriendly, we can store a fixed-length signature of the > >> rules instead. For example, the signature can be calculated by > >> performing XOR operation on IP addresses. Both design can avoid > >> unnecessary pointer dereferences. > > > > > > Since DPDK does burst mode already, GRO is a lot less relevant. > > GRO in Linux was invented because there is no burst mode in the receive= API. > > > > If you look at VPP in FD.io you will see they already do aggregration a= nd > > steering at the higher level in the stack. > > > > The point of GRO is that it is generic, no driver changes are necessary= . > > Your proposal would add a lot of overhead, and cause drivers to have to > > be aware of higher level flows. >=20 > NACK >=20 > The design is not super clear to me here and we need to understand the im= pact to DPDK, performance and the application. I would like to > have a clean transparent design to the application and as little impact o= n performance as possible. >=20 > Let discuss this as I am not sure my previous concerns were addressed in = this RFC. >=20 I would agree that design looks overcomplicated and strange: If GRO can (and supposed to be) done fully in SW, why do we need to modify = PMDs at all, why it can't be just a standalone DPDK library that user can use on his/her= convenience? I'd suggest to start with some simple and most widespread case (TCP?) and t= ry to implement a library for it first: something similar to what we have for ip reassembly= . Konstantin =20