On Thu, Nov 23, 2023 at 1:36 AM Jiri Pirko <jiri@xxxxxxxxxxx> wrote: > > Wed, Nov 22, 2023 at 08:35:21PM CET, jhs@xxxxxxxxxxxx wrote: > >On Wed, Nov 22, 2023 at 1:31 PM Jiri Pirko <jiri@xxxxxxxxxxx> wrote: > >> > >> Wed, Nov 22, 2023 at 04:14:02PM CET, jhs@xxxxxxxxxxxx wrote: > >> >On Wed, Nov 22, 2023 at 4:25 AM Jiri Pirko <jiri@xxxxxxxxxxx> wrote: > >> >> > >> >> Tue, Nov 21, 2023 at 04:21:44PM CET, jhs@xxxxxxxxxxxx wrote: > >> >> >On Tue, Nov 21, 2023 at 9:19 AM Jiri Pirko <jiri@xxxxxxxxxxx> wrote: > >> >> >> > >> >> >> Tue, Nov 21, 2023 at 02:47:40PM CET, jhs@xxxxxxxxxxxx wrote: > >> >> >> >On Tue, Nov 21, 2023 at 8:06 AM Jiri Pirko <jiri@xxxxxxxxxxx> wrote: > >> >> >> >> > >> >> >> >> Mon, Nov 20, 2023 at 11:56:50PM CET, jhs@xxxxxxxxxxxx wrote: > >> >> >> >> >On Mon, Nov 20, 2023 at 4:49 PM Daniel Borkmann <daniel@xxxxxxxxxxxxx> wrote: > >> >> >> >> >> > >> >> >> >> >> On 11/20/23 8:56 PM, Jamal Hadi Salim wrote: > >> >> >> >> >> > On Mon, Nov 20, 2023 at 1:10 PM Jiri Pirko <jiri@xxxxxxxxxxx> wrote: > >> >> >> >> >> >> Mon, Nov 20, 2023 at 03:23:59PM CET, jhs@xxxxxxxxxxxx wrote: > >> >> >> >> > >> >> >> >> [...] > >> >> >> >> > >> >> >> >> > > >> >> >> >> >> tc BPF and XDP already have widely used infrastructure and can be developed > >> >> >> >> >> against libbpf or other user space libraries for a user space control plane. > >> >> >> >> >> With 'control plane' you refer here to the tc / netlink shim you've built, > >> >> >> >> >> but looking at the tc command line examples, this doesn't really provide a > >> >> >> >> >> good user experience (you call it p4 but people load bpf obj files). If the > >> >> >> >> >> expectation is that an operator should run tc commands, then neither it's > >> >> >> >> >> a nice experience for p4 nor for BPF folks. From a BPF PoV, we moved over > >> >> >> >> >> to bpf_mprog and plan to also extend this for XDP to have a common look and > >> >> >> >> >> feel wrt networking for developers. Why can't this be reused? > >> >> >> >> > > >> >> >> >> >The filter loading which loads the program is considered pipeline > >> >> >> >> >instantiation - consider it as "provisioning" more than "control" > >> >> >> >> >which runs at runtime. "control" is purely netlink based. The iproute2 > >> >> >> >> >code we use links libbpf for example for the filter. If we can achieve > >> >> >> >> >the same with bpf_mprog then sure - we just dont want to loose > >> >> >> >> >functionality though. off top of my head, some sample space: > >> >> >> >> >- we could have multiple pipelines with different priorities (which tc > >> >> >> >> >provides to us) - and each pipeline may have its own logic with many > >> >> >> >> >tables etc (and the choice to iterate the next one is essentially > >> >> >> >> >encoded in the tc action codes) > >> >> >> >> >- we use tc block to map groups of ports (which i dont think bpf has > >> >> >> >> >internal access of) > >> >> >> >> > > >> >> >> >> >In regards to usability: no i dont expect someone doing things at > >> >> >> >> >scale to use command line tc. The APIs are via netlink. But the tc cli > >> >> >> >> >is must for the rest of the masses per our traditions. Also i really > >> >> >> >> > >> >> >> >> I don't follow. You repeatedly mention "the must of the traditional tc > >> >> >> >> cli", but what of the existing traditional cli you use for p4tc? > >> >> >> >> If I look at the examples, pretty much everything looks new to me. > >> >> >> >> Example: > >> >> >> >> > >> >> >> >> tc p4ctrl create myprog/table/mytable dstAddr 10.0.1.2/32 \ > >> >> >> >> action send_to_port param port eno1 > >> >> >> >> > >> >> >> >> This is just TC/RTnetlink used as a channel to pass new things over. If > >> >> >> >> that is the case, what's traditional here? > >> >> >> >> > >> >> >> > > >> >> >> > > >> >> >> >What is not traditional about it? > >> >> >> > >> >> >> Okay, so in that case, the following example communitating with > >> >> >> userspace deamon using imaginary "p4ctrl" app is equally traditional: > >> >> >> $ p4ctrl create myprog/table/mytable dstAddr 10.0.1.2/32 \ > >> >> >> action send_to_port param port eno1 > >> >> > > >> >> >Huh? Thats just an application - classical tc which part of iproute2 > >> >> >that is sending to the kernel, no different than "tc flower.." > >> >> >Where do you get the "userspace" daemon part? Yes, you can write a > >> >> >daemon but it will use the same APIs as tc. > >> >> > >> >> Okay, so which part is the "tradition"? > >> >> > >> > > >> >Provides tooling via tc cli that _everyone_ in the tc world is > >> >familiar with - which uses the same syntax as other tc extensions do, > >> >same expectations (eg events, request responses, familiar commands for > >> >dumping, flushing etc). Basically someone familiar with tc will pick > >> >this up and operate it very quickly and would have an easier time > >> >debugging it. > >> >There are caveats - as will be with all new classifiers - but those > >> >are within reason. > >> > >> Okay, so syntax familiarity wise, what's the difference between > >> following 2 approaches: > >> $ tc p4ctrl create myprog/table/mytable dstAddr 10.0.1.2/32 \ > >> action send_to_port param port eno1 > >> $ p4ctrl create myprog/table/mytable dstAddr 10.0.1.2/32 \ > >> action send_to_port param port eno1 > >> ? > >> > >> > >> > > >> >> >> > >> >> >> > > >> >> >> >> > >> >> >> >> >didnt even want to use ebpf at all for operator experience reasons - > >> >> >> >> >it requires a compilation of the code and an extra loading compared to > >> >> >> >> >what our original u32/pedit code offered. > >> >> >> >> > > >> >> >> >> >> I don't quite follow why not most of this could be implemented entirely in > >> >> >> >> >> user space without the detour of this and you would provide a developer > >> >> >> >> >> library which could then be integrated into a p4 runtime/frontend? This > >> >> >> >> >> way users never interface with ebpf parts nor tc given they also shouldn't > >> >> >> >> >> have to - it's an implementation detail. This is what John was also pointing > >> >> >> >> >> out earlier. > >> >> >> >> >> > >> >> >> >> > > >> >> >> >> >Netlink is the API. We will provide a library for object manipulation > >> >> >> >> >which abstracts away the need to know netlink. Someone who for their > >> >> >> >> >own reasons wants to use p4runtime or TDI could write on top of this. > >> >> >> >> >I would not design a kernel interface to just meet p4runtime (we > >> >> >> >> >already have TDI which came later which does things differently). So i > >> >> >> >> >expect us to support both those two. And if i was to do something on > >> >> >> >> >SDN that was more robust i would write my own that still uses these > >> >> >> >> >netlink interfaces. > >> >> >> >> > >> >> >> >> Actually, what Daniel says about the p4 library used as a backend to p4 > >> >> >> >> frontend is pretty much aligned what I claimed on the p4 calls couple of > >> >> >> >> times. If you have this p4 userspace tooling, it is easy for offloads to > >> >> >> >> replace the backed by vendor-specific library which allows p4 offload > >> >> >> >> suitable for all vendors (your plan of p4tc offload does not work well > >> >> >> >> for our hw, as we repeatedly claimed). > >> >> >> >> > >> >> >> > > >> >> >> >That's you - NVIDIA. You have chosen a path away from the kernel > >> >> >> >towards DOCA. I understand NVIDIA's frustration with dealing with > >> >> >> >upstream process (which has been cited to me as a good reason for > >> >> >> >DOCA) but please dont impose these values and your politics on other > >> >> >> >vendors(Intel, AMD for example) who are more than willing to invest > >> >> >> >into making the kernel interfaces the path forward. Your choice. > >> >> >> > >> >> >> No, you are missing the point. This has nothing to do with DOCA. > >> >> > > >> >> >Right Jiri ;-> > >> >> > > >> >> >> This > >> >> >> has to do with the simple limitation of your offload assuming there are > >> >> >> no runtime changes in the compiled pipeline. For Intel, maybe they > >> >> >> aren't, and it's a good fit for them. All I say is, that it is not the > >> >> >> good fit for everyone. > >> >> > > >> >> > a) it is not part of the P4 spec to dynamically make changes to the > >> >> >datapath pipeline after it is create and we are discussing a P4 > >> >> > >> >> Isn't this up to the implementation? I mean from the p4 perspective, > >> >> everything is static. Hw might need to reshuffle the pipeline internally > >> >> during rule insertion/remove in order to optimize the layout. > >> >> > >> > > >> >But do note: the focus here is on P4 (hence the name P4TC). > >> > > >> >> >implementation not an extension that would add more value b) We are > >> >> >more than happy to add extensions in the future to accomodate for > >> >> >features but first _P4 spec_ must be met c) we had longer discussions > >> >> >with Matty, Khalid and the Rice folks who wrote a paper on that topic > >> >> >which you probably didnt attend and everything that needs to be done > >> >> >can be from user space today for all those optimizations. > >> >> > > >> >> >Conclusion is: For what you need to do (which i dont believe is a > >> >> >limitation in your hardware rather a design decision on your part) run > >> >> >your user space daemon, do optimizations and update the datapath. > >> >> >Everybody is happy. > >> >> > >> >> Should the userspace daemon listen on inserted rules to be offloade > >> >> over netlink? > >> >> > >> > > >> >I mean you could if you wanted to given this is just traditional > >> >netlink which emits events (with some filtering when we integrate the > >> >filter approach). But why? > >> > >> Nevermind. > >> > >> > >> > > >> >> > > >> >> >> > >> >> >> >Nobody is stopping you from offering your customers proprietary > >> >> >> >solutions which include a specific ebpf approach alongside DOCA. We > >> >> >> >believe that a singular interface regardless of the vendor is the > >> >> >> >right way forward. IMHO, this siloing that unfortunately is also added > >> >> >> >by eBPF being a double edged sword is not good for the community. > >> >> >> > > >> >> >> >> As I also said on the p4 call couple of times, I don't see the kernel > >> >> >> >> as the correct place to do the p4 abstractions. Why don't you do it in > >> >> >> >> userspace and give vendors possiblity to have p4 backends with compilers, > >> >> >> >> runtime optimizations etc in userspace, talking to the HW in the > >> >> >> >> vendor-suitable way too. Then the SW implementation could be easily eBPF > >> >> >> >> and the main reason (I believe) why you need to have this is TC > >> >> >> >> (offload) is then void. > >> >> >> >> > >> >> >> >> The "everyone wants to use TC/netlink" claim does not seem correct > >> >> >> >> to me. Why not to have one Linux p4 solution that fits everyones needs? > >> >> >> > > >> >> >> >You mean more fitting to the DOCA world? no, because iam a kernel > >> >> >> > >> >> >> Again, this has 0 relation to DOCA. > >> >> >> > >> >> >> > >> >> >> >first person and kernel interfaces are good for everyone. > >> >> >> > >> >> >> Yeah, not really. Not always the kernel is the right answer. Your/Intel > >> >> >> plan to handle the offload by: > >> >> >> 1) abuse devlink to flash p4 binary > >> >> >> 2) parse the binary in kernel to match to the table ids of rules coming > >> >> >> from p4tc ndo_setup_tc > >> >> >> 3) abuse devlink to flash p4 binary for tc-flower > >> >> >> 4) parse the binary in kernel to match to the table ids of rules coming > >> >> >> from tc-flower ndo_setup_tc > >> >> >> is really something that is making me a little bit nauseous. > >> >> >> > >> >> >> If you don't have a feasible plan to do the offload, p4tc does not make > >> >> >> sense to me to be honest. > >> >> > > >> >> >You mean if there's no plan to match your (NVIDIA?) point of view. > >> >> >For #1 - how's this different from DDP? Wasnt that your suggestion to > >> >> > >> >> I doubt that. Any flashing-blob-parsing-in-kernel is something I'm > >> >> opposed to from day 1. > >> >> > >> >> > >> > > >> >Oh well - it is in the kernel and it works fine tbh. > >> > > >> >> >begin with? For #2 Nobody is proposing to do anything of the sort. The > >> >> >ndo is passed IDs for the objects and associated contents. For #3+#4 > >> >> > >> >> During offload, you need to parse the blob in driver to be able to match > >> >> the ids with blob entities. That was presented by you/Intel in the past > >> >> IIRC. > >> >> > >> > > >> >You are correct - in case of offload the netlink IDs will have to be > >> >authenticated against what the hardware can accept, but the devlink > >> >flash use i believe was from you as a compromise. > >> > >> Definitelly not. I'm against devlink abuse for this from day 1. > >> > >> > >> > > >> >> > >> >> >tc flower thing has nothing to do with P4TC that was just some random > >> >> >proposal someone made seeing if they could ride on top of P4TC. > >> >> > >> >> Yeah, it's not yet merged and already mentally used for abuse. I love > >> >> that :) > >> >> > >> >> > > >> >> >Besides this nobody really has to satisfy your point of view - like i > >> >> >said earlier feel free to provide proprietary solutions. From a > >> >> >consumer perspective I would not want to deal with 4 different > >> >> >vendors with 4 different proprietary approaches. The kernel is the > >> >> >unifying part. You seemed happier with tc flower just not with the > >> >> > >> >> Yeah, that is my point, why the unifying part can't be a userspace > >> >> daemon/library with multiple backends (p4tc, bpf, vendorX, vendorY, ..)? > >> >> > >> >> I just don't see the kernel as a good fit for abstraction here, > >> >> given the fact that the vendor compilers does not run in kernel. > >> >> That is breaking your model. > >> >> > >> > > >> >Jiri - we want to support P4, first. Like you said the P4 pipeline, > >> >once installed is static. > >> >P4 doesnt allow dynamic update of the pipeline. For example, once you > >> >say "here are my 14 tables and their associated actions and here's how > >> >the pipeline main control (on how to iterate the tables etc) is going > >> >to be" and after you instantiate/activate that pipeline, you dont go > >> >back 5 minutes later and say "sorry, please introduce table 15, which > >> >i want you to walk to after you visit table 3 if metadata foo is 5" or > >> >"shoot, let's change that table 5 to be exact instead of LPM". It's > >> >not anywhere in the spec. > >> >That doesnt mean it is not useful thing to have - but it is an > >> >invention that has _nothing to do with the P4 spec_; so saying a P4 > >> >implementation must support it is a bit out of scope and there are > >> >vendors with hardware who support P4 today that dont need any of this. > >> > >> I'm not talking about the spec. I'm talking about the offload > >> implemetation, the offload compiler the offload runtime manager. You > >> don't have those in kernel. That is the issue. The runtime manager is > >> the one to decide and reshuffle the hw internals. Again, this has > >> nothing to do with p4 frontend. This is offload implementation. > >> > >> And that is why I believe your p4 kernel implementation is unoffloadable. > >> And if it is unoffloadable, do we really need it? IDK. > >> > > > >Say what? > >It's not offloadable in your hardware, you mean? Because i have beside > >me here an intel e2000 which offloads just fine (and the AMD folks > >seem fine too). > > Will Intel and AMD have compiler in kernel, so no blob transfer and > parsing it in kernel wound not be needed? No. By that definition anything that parses anything is a compiler. > > >If your view is that all these runtime optimization surmount to a > >compiler in the kernel/driver that is your, well, your view. In my > >view (and others have said this to you already) the P4C compiler is > >responsible for resource optimizations. The hardware supports P4, you > >give it constraints and it knows what to do. At runtime, anything a > >driver needs to do for resource optimization (resorting, reshuffling > >etc), that is not a P4 problem - sorry if you have issues in your > >architecture approach. > > Sure, it is the offload implementation problem. And for them, you need > to use userspace components. And that is the problem. This discussion > leads nowhere, I don't know how differently I should describe this. Jiri's - that's your view based on whatever design you have in your mind. This has nothing to do with P4. So let me repeat again: 1) A vendor's backend for P4 when it compiles ensures that resource constraints are taken care of. 2) The same program can run in s/w. 3) It makes *ZERO* sense to mix vendor specific constraint optimization(what you described as resorting, reshuffling etc) as part of P4TC or P4. Absolutely nothing to do with either. Write a background task, specific to you, if you feel you need to move things around at runtime. We agree on one thing at least: This discussion is going nowhere. cheers, jamal > > > >> >In my opinion that is a feature that could be added later out of > >> >necessity (there is some good niche value in being able to add some > >> >"dynamicism" to any pipeline) and influence the P4 standards on why it > >> >is needed. > >> >It should be doable today in a brute force way (this is just one > >> >suggestion that came to me when Rice University/Nvidia presented[1]); > >> >i am sure there are other approaches and the idea is by no means > >> >proven. > >> > > >> >1) User space Creates/compiles/Adds/activate your program that has 14 > >> >tables at tc prio X chain Y > >> >2) a) 5 minutes later user space decides it wants to change and add > >> >table 3 after table 15, visited when metadata foo=5 > >> > b) your compiler in user space compiles a brand new program which > >> >satisfies #2a (how this program was authored is out of scope of > >> >discussion) > >> > c) user space adds the new program at tc prio X+1 chain Y or another chain Z > >> > d) user space delete tc prio X chain Y (and make sure your packets > >> >entry point is whatever #c is) > >> > >> I never suggested anything like what you describe. I'm not sure why you > >> think so. > > > >It's the same class of problems - the paper i pointed to (coauthored > >by Matty and others) has runtime resource optimizations which are > >tantamount to changing the nature of the pipeline. We may need to > >profile in the kernel but all those optimizations can be derived in > >user space using the approach I described. > > > >cheers, > >jamal > > > > > >> >[1] https://www.cs.rice.edu/~eugeneng/papers/SIGCOMM23-Pipeleon.pdf > >> > > >> >> > >> >> >kernel process - which is ironically the same thing we are going > >> >> >through here ;-> > >> >> > > >> >> >cheers, > >> >> >jamal > >> >> > > >> >> >> > >> >> >> > > >> >> >> >cheers, > >> >> >> >jamal
