From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mga04.intel.com (mga04.intel.com [192.55.52.120]) by dpdk.org (Postfix) with ESMTP id 68A0C1023 for ; Tue, 24 Jan 2017 21:09:09 +0100 (CET) Received: from orsmga002.jf.intel.com ([10.7.209.21]) by fmsmga104.fm.intel.com with ESMTP; 24 Jan 2017 12:09:08 -0800 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.33,279,1477983600"; d="scan'208";a="34923258" Received: from fmsmsx107.amr.corp.intel.com ([10.18.124.205]) by orsmga002.jf.intel.com with ESMTP; 24 Jan 2017 12:09:08 -0800 Received: from fmsmsx153.amr.corp.intel.com (10.18.125.6) by fmsmsx107.amr.corp.intel.com (10.18.124.205) with Microsoft SMTP Server (TLS) id 14.3.248.2; Tue, 24 Jan 2017 12:09:08 -0800 Received: from fmsmsx113.amr.corp.intel.com ([169.254.13.230]) by FMSMSX153.amr.corp.intel.com ([169.254.9.17]) with mapi id 14.03.0248.002; Tue, 24 Jan 2017 12:09:08 -0800 From: "Wiles, Keith" To: "Ananyev, Konstantin" CC: Stephen Hemminger , "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: AQHSdXkcV6LeBFKVAEOr1Y1FPpUEfqFG09oAgABNfYCAAEA9AIAAPjGAgABV5ACAAEdgAIAAUwGAgAAGj4A= Date: Tue, 24 Jan 2017 20:09:07 +0000 Message-ID: References: <1485176592-111525-1-git-send-email-jiayu.hu@intel.com> <20170123091550.212dca35@xeon-e3> <6B5C6BED-CAD4-4C51-8FB7-8509663B813B@intel.com> <2601191342CEEE43887BDE71AB9772583F10AD94@irsmsx105.ger.corp.intel.com> <1F520FF1-C38B-483B-95E1-FBD4C631E7D2@intel.com> <2601191342CEEE43887BDE71AB9772583F10AEBD@irsmsx105.ger.corp.intel.com> <6D277342-5212-462F-A507-93B63E86DA90@intel.com> <2601191342CEEE43887BDE71AB9772583F10C6DC@irsmsx105.ger.corp.intel.com> In-Reply-To: <2601191342CEEE43887BDE71AB9772583F10C6DC@irsmsx105.ger.corp.intel.com> Accept-Language: en-US Content-Language: en-US X-MS-Has-Attach: X-MS-TNEF-Correlator: x-originating-ip: [10.34.73.134] Content-Type: text/plain; charset="us-ascii" Content-ID: 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 20:09:11 -0000 > On Jan 24, 2017, at 12:45 PM, Ananyev, Konstantin wrote: >=20 >=20 >=20 >> -----Original Message----- >> From: Wiles, Keith >> Sent: Tuesday, January 24, 2017 2:49 PM >> To: Ananyev, Konstantin >> Cc: Stephen Hemminger ; Hu, Jiayu ; dev@dpdk.org; Kinsella, Ray >> ; Gilmore, Walter E = ; Venkatesan, Venky ; >> yuanhan.liu@linux.intel.com >> Subject: Re: [dpdk-dev] [RFC] Add GRO support in DPDK >>=20 >>=20 >>> On Jan 24, 2017, at 3:33 AM, Ananyev, Konstantin wrote: >>>=20 >>>=20 >>>=20 >>>> -----Original Message----- >>>> From: Wiles, Keith >>>> Sent: Tuesday, January 24, 2017 5:26 AM >>>> To: Ananyev, Konstantin >>>> Cc: Stephen Hemminger ; Hu, Jiayu ; dev@dpdk.org; Kinsella, Ray >>>> ; 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 6:43 PM, Ananyev, Konstantin wrote: >>>>>=20 >>>>>=20 >>>>>=20 >>>>>> -----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: >>>>>>>=20 >>>>>>> On Mon, 23 Jan 2017 21:03:12 +0800 >>>>>>> Jiayu Hu wrote: >>>>>>>=20 >>>>>>>> With the support of hardware segmentation techniques in DPDK, the >>>>>>>> networking stack overheads of send-side of applications, which dir= ectly >>>>>>>> leverage DPDK, have been greatly reduced. But for receive-side, nu= mbers of >>>>>>>> segmented packets seriously burden the networking stack of applica= tions. >>>>>>>> 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 doe= sn't >>>>>>>> support GRO. Therefore, we propose to add GRO support in DPDK, and= this >>>>>>>> RFC is used to explain the basic DPDK GRO design. >>>>>>>>=20 >>>>>>>> DPDK GRO is a SW-based packets assembly library, which provides GR= O >>>>>>>> abilities for numbers of protocols. In DPDK GRO, packets are merge= d >>>>>>>> before returning to applications and after receiving from drivers. >>>>>>>>=20 >>>>>>>> In DPDK, GRO is a capability of NIC drivers. That support GRO or n= ot and >>>>>>>> what GRO types are supported are up to NIC drivers. Different driv= ers may >>>>>>>> support different GRO types. By default, drivers enable all suppor= ted GRO >>>>>>>> types. For applications, they can inquire the supported GRO types = by >>>>>>>> each driver, and can control what GRO types are applied. For examp= le, >>>>>>>> ixgbe supports TCP and UDP GRO, but the application just needs TCP= GRO. >>>>>>>> The application can disable ixgbe UDP GRO. >>>>>>>>=20 >>>>>>>> To support GRO, a driver should provide a way to tell applications= what >>>>>>>> GRO types are supported, and provides a GRO function, which is in = charge >>>>>>>> of assembling packets. Since different drivers may support differe= nt GRO >>>>>>>> types, their GRO functions may be different. For applications, the= y don't >>>>>>>> need extra operations to enable GRO. But if there are some GRO typ= es that >>>>>>>> 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. >>>>>>>>=20 >>>>>>>> The GRO function processes numbers of packets at a time. In each >>>>>>>> invocation, what GRO types are applied depends on applications, an= d the >>>>>>>> amount of packets to merge depends on the networking status and >>>>>>>> applications. Specifically, applications determine the maximum num= ber of >>>>>>>> packets to be processed by the GRO function, but how many packets = are >>>>>>>> actually processed depends on if there are available packets to re= ceive. >>>>>>>> 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 reassembl= e the >>>>>>>> given packets, the GRO function performs an "assembly procedure" o= n each >>>>>>>> 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 o= f a >>>>>>>> specific type. For example, TCPv4 assembly function merges packet= s >>>>>>>> whose L3 IPv4 and L4 is TCP. Each L4 assembly function has a pack= et >>>>>>>> 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). I= f >>>>>>>> finds, merges it and packetX via chaining them together; if doesn= 't, >>>>>>>> allocates a new array element to store packetX and updates elemen= t >>>>>>>> number of the array. >>>>>>>> After performing the assembly procedure to all packets, the GRO fu= nction >>>>>>>> combines the results of all packet arrays, and returns these packe= ts to >>>>>>>> applications. >>>>>>>>=20 >>>>>>>> There are lots of ways to implement the above design in DPDK. One = of the >>>>>>>> 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 t= he >>>>>>>> GRO function should be like xxx_gro_receive (e.g. ixgbe_gro_recei= ve). >>>>>>>> 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 drive= r >>>>>>>> return packets as many as possible until the packet number meets = the >>>>>>>> demand of applications or there are not available packets to rece= ive. >>>>>>>> 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 me= rge >>>>>>>> are passed by resetting RX callback parameters. It can be achieve= d by >>>>>>>> invoking rte_eth_rx_callback; >>>>>>>> d. Simply, we can just store packet addresses into the packet arr= ay. >>>>>>>> To check one element, we need to fetch the packet via its address= . >>>>>>>> However, this simple design is not efficient enough. Since whenev= er >>>>>>>> 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 structu= re >>>>>>>> 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. >>>>>>>=20 >>>>>>>=20 >>>>>>> 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 rec= eive API. >>>>>>>=20 >>>>>>> If you look at VPP in FD.io you will see they already do aggregrati= on and >>>>>>> steering at the higher level in the stack. >>>>>>>=20 >>>>>>> The point of GRO is that it is generic, no driver changes are neces= sary. >>>>>>> Your proposal would add a lot of overhead, and cause drivers to hav= e to >>>>>>> be aware of higher level flows. >>>>>>=20 >>>>>> NACK >>>>>>=20 >>>>>> The design is not super clear to me here and we need to understand t= he impact to DPDK, performance and the application. I would >> like >>>> to >>>>>> have a clean transparent design to the application and as little imp= act on performance as possible. >>>>>>=20 >>>>>> Let discuss this as I am not sure my previous concerns were addresse= d in this RFC. >>>>>>=20 >>>>>=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 m= odify PMDs at all, >>>>> why it can't be just a standalone DPDK library that user can use on h= is/her convenience? >>>>> I'd suggest to start with some simple and most widespread case (TCP?)= and try to implement >>>>> a library for it first: something similar to what we have for ip reas= sembly. >>>>=20 >>>> The reason this should not be a library the application calls is to al= low for a transparent design for HW and SW support of this feature. >> Using >>>> the SW version the application should not need to understand (other th= en performance) that GRO is being done for this port. >>>>=20 >>>=20 >>> Why is that? >>> Let say we have ip reassembly library that is called explicitly by the = application. >>> I think for L4 grouping we can do the same. >>> After all it is a pure SW feature, so to me it makes sense to allow app= lication to decide >>> when/where to call it. >>> Again it would allow people to develop/use it without any modifications= in current PMDs. >>=20 >> I guess I did not make it clear, we need to support HW and this SW versi= on transparently just as we handle other features in HW/SW under a >> generic API for DPDK. >=20 > Ok, I probably wasn't very clear too. > What I meant: > Let's try to implement GRO (in SW) as a standalone DPDK library, > with clean & simple interface and see how fast and useful it would be. > We can refer to it as step 1. > When (if) we'll have step 1 in place, then we can start thinking > about adding combined HW/SW solution for it (step 2). > I think at that stage it would be much clearer: > is there any point in it at all, > and if yes, how it should be done: > -changes at rte_ethedev or on PMD layers or both > - would changes at rte_ethdev API be needed and if yes what particular, = etc. >=20 > From my perspective, without step 1 in place, there is no much point in = approaching step 2. Currently I believe they have a SW library version of the code, but I think= we need to look at the design in that form. At this time the current desig= n or code is not what I would expect needs to be done for the transparent v= ersion. To many interactions with the application and a separate Rx/Tx func= tions were being used (If I remember correctly) >=20 > BTW, any particular HW you have in mind? > Currently, as I can see LRO (HW) is supported only by ixgbe and probably = by viritual PMDs (virtio/vmxent3). > Though even for ixgbe there are plenty of limitations: SRIOV mode should = be off, HW CRC stropping should be off, etc. > So my guess, right now step 1 is much more useful and feasible. >=20 >>=20 >>>=20 >>>> As I was told the Linux kernel hides this features and make it transpa= rent. >>>=20 >>> Yes, but DPDK does a lot things in a different way. >>> So it doesn't look like a compelling reason for me :) >>=20 >> Just looking at different options here and it is a compelling reason to = me as it enforces the design can be transparent to the application. >> Having the application in a NFV deciding on hw or sw or both is not a go= od place to put that logic IMO. >=20 > Actually could you provide an example of linux NIC driver, that uses HW o= ffloads (and which) to implement GRO? > I presume some might use HW generated hashes, but apart from that, when H= W performs actual packet grouping? > From what I've seen Intel ones rely SW implementation for that. > But I am not a linux/GRO expert, so feel free to correct me here. > Konstantin=20 Regards, Keith