> On Jan 24, 2017, at 2:04 PM, Stephen Hemminger <step...@networkplumber.org> > wrote: > > On Tue, 24 Jan 2017 20:09:07 +0000 > "Wiles, Keith" <keith.wi...@intel.com> wrote: > >>> On Jan 24, 2017, at 12:45 PM, Ananyev, Konstantin >>> <konstantin.anan...@intel.com> wrote: >>> >>> >>> >>>> -----Original Message----- >>>> From: Wiles, Keith >>>> Sent: Tuesday, January 24, 2017 2:49 PM >>>> To: Ananyev, Konstantin <konstantin.anan...@intel.com> >>>> Cc: Stephen Hemminger <step...@networkplumber.org>; Hu, Jiayu >>>> <jiayu...@intel.com>; dev@dpdk.org; Kinsella, Ray >>>> <ray.kinse...@intel.com>; Gilmore, Walter E <walter.e.gilm...@intel.com>; >>>> Venkatesan, Venky <venky.venkate...@intel.com>; >>>> yuanhan....@linux.intel.com >>>> Subject: Re: [dpdk-dev] [RFC] Add GRO support in DPDK >>>> >>>> >>>>> On Jan 24, 2017, at 3:33 AM, Ananyev, Konstantin >>>>> <konstantin.anan...@intel.com> wrote: >>>>> >>>>> >>>>> >>>>>> -----Original Message----- >>>>>> From: Wiles, Keith >>>>>> Sent: Tuesday, January 24, 2017 5:26 AM >>>>>> To: Ananyev, Konstantin <konstantin.anan...@intel.com> >>>>>> Cc: Stephen Hemminger <step...@networkplumber.org>; Hu, Jiayu >>>>>> <jiayu...@intel.com>; dev@dpdk.org; Kinsella, Ray >>>>>> <ray.kinse...@intel.com>; Gilmore, Walter E >>>>>> <walter.e.gilm...@intel.com>; Venkatesan, Venky >>>>>> <venky.venkate...@intel.com>; >>>>>> yuanhan....@linux.intel.com >>>>>> Subject: Re: [dpdk-dev] [RFC] Add GRO support in DPDK >>>>>> >>>>>> >>>>>>> On Jan 23, 2017, at 6:43 PM, Ananyev, Konstantin >>>>>>> <konstantin.anan...@intel.com> wrote: >>>>>>> >>>>>>> >>>>>>> >>>>>>>> -----Original Message----- >>>>>>>> From: Wiles, Keith >>>>>>>> Sent: Monday, January 23, 2017 9:53 PM >>>>>>>> To: Stephen Hemminger <step...@networkplumber.org> >>>>>>>> Cc: Hu, Jiayu <jiayu...@intel.com>; dev@dpdk.org; Kinsella, Ray >>>>>>>> <ray.kinse...@intel.com>; Ananyev, Konstantin >>>>>>>> <konstantin.anan...@intel.com>; Gilmore, Walter E >>>>>>>> <walter.e.gilm...@intel.com>; Venkatesan, Venky >>>>>> <venky.venkate...@intel.com>; >>>>>>>> yuanhan....@linux.intel.com >>>>>>>> Subject: Re: [dpdk-dev] [RFC] Add GRO support in DPDK >>>>>>>> >>>>>>>> >>>>>>>>> On Jan 23, 2017, at 10:15 AM, Stephen Hemminger >>>>>>>>> <step...@networkplumber.org> wrote: >>>>>>>>> >>>>>>>>> On Mon, 23 Jan 2017 21:03:12 +0800 >>>>>>>>> Jiayu Hu <jiayu...@intel.com> wrote: >>>>>>>>> >>>>>>>>>> With the support of hardware segmentation techniques in DPDK, the >>>>>>>>>> networking stack overheads of send-side of applications, which >>>>>>>>>> directly >>>>>>>>>> leverage DPDK, have been greatly reduced. But for receive-side, >>>>>>>>>> numbers of >>>>>>>>>> segmented packets seriously burden the networking stack of >>>>>>>>>> applications. >>>>>>>>>> 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 >>>>>>>>>> this >>>>>>>>>> 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 >>>>>>>>>> and >>>>>>>>>> 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 >>>>>>>>>> what >>>>>>>>>> GRO types are supported, and provides a GRO function, which is in >>>>>>>>>> charge >>>>>>>>>> of assembling packets. Since different drivers may support different >>>>>>>>>> GRO >>>>>>>>>> types, their GRO functions may be different. For applications, they >>>>>>>>>> don't >>>>>>>>>> need extra operations to enable GRO. But if there are some GRO types >>>>>>>>>> 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. >>>>>>>>>> >>>>>>>>>> The GRO function processes numbers of packets at a time. In each >>>>>>>>>> invocation, what GRO types are applied depends on applications, and >>>>>>>>>> the >>>>>>>>>> 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 >>>>>>>>>> receive. >>>>>>>>>> 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 >>>>>>>>>> the >>>>>>>>>> given packets, the GRO function performs an "assembly procedure" on >>>>>>>>>> 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 >>>>>>>>>> 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 >>>>>>>>>> function >>>>>>>>>> combines the results of all packet arrays, and returns these packets >>>>>>>>>> to >>>>>>>>>> applications. >>>>>>>>>> >>>>>>>>>> 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 >>>>>>>>>> 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 >>>>>>>>> and >>>>>>>>> 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. >>>>>>>> >>>>>>>> NACK >>>>>>>> >>>>>>>> The design is not super clear to me here and we need to understand the >>>>>>>> impact to DPDK, performance and the application. I would >>>> like >>>>>> to >>>>>>>> have a clean transparent design to the application and as little >>>>>>>> impact on performance as possible. >>>>>>>> >>>>>>>> Let discuss this as I am not sure my previous concerns were addressed >>>>>>>> in this RFC. >>>>>>>> >>>>>>> >>>>>>> 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 try to implement >>>>>>> a library for it first: something similar to what we have for ip >>>>>>> reassembly. >>>>>> >>>>>> The reason this should not be a library the application calls is to >>>>>> allow for a transparent design for HW and SW support of this feature. >>>> Using >>>>>> the SW version the application should not need to understand (other then >>>>>> performance) that GRO is being done for this port. >>>>>> >>>>> >>>>> 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 >>>>> application to decide >>>>> when/where to call it. >>>>> Again it would allow people to develop/use it without any modifications >>>>> in current PMDs. >>>> >>>> I guess I did not make it clear, we need to support HW and this SW version >>>> transparently just as we handle other features in HW/SW under a >>>> generic API for DPDK. >>> >>> 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. >>> >>> 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 design >> or code is not what I would expect needs to be done for the transparent >> version. To many interactions with the application and a separate Rx/Tx >> functions were being used (If I remember correctly) >> >>> >>> 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. >>> >>>> >>>>> >>>>>> As I was told the Linux kernel hides this features and make it >>>>>> transparent. >>>>> >>>>> Yes, but DPDK does a lot things in a different way. >>>>> So it doesn't look like a compelling reason for me :) >>>> >>>> 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 good >>>> place to put that logic IMO. >>> >>> Actually could you provide an example of linux NIC driver, that uses HW >>> offloads (and which) to implement GRO? >>> I presume some might use HW generated hashes, but apart from that, when HW >>> 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 >> >> Regards, >> Keith >> > > Linux uses a push (rather than DPDK pull) model for packet receiving. > The Linux driver pushes packets into GRO by calling napi_gro_receive. > > Since DPDK is pull model the API would be simpler. > it could be as simple as: > nb = rte_eth_rx_burst(port, rx_pkts, N); > nb = rte_rx_gro(port, rx_pkts, gro_pkts, nb); > > I agree with others, look at ip reassembly library as example. > Also, GRO does not make sense for applications which already do the same > vector flow > processing like VPP which is one reason it should be optional.
I agree it should be option, but I worry about making it an example. I would like to see the GRO to be more transparent to the application and supported as a generic feature for DPDK. Maybe the application needs to request the support or it is a config option. The problem with config options is they are hard to test and testing becomes complexed. Can we not figure out a way to add the feature inline instead of the application needing to call these APIs? It would be nice to have IP fragmentation also a optional feature to the rx/tx ethdev call. It would take it out of the example zone and move it into DPDK as a real feature. Today we expect the application to chain all of these little bits outside of DPDK into something useful, can we help fix that problem? > Regards, Keith
