Thu, Nov 23, 2023 at 02:22:11PM CET, jhs@xxxxxxxxxxxx wrote: >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 I never suggested for it to be part of P4tc of P4. I don't know why you think so. >background task, specific to you, if you feel you need to move things >around at runtime. Yeah, that backgroud task is in userspace. > >We agree on one thing at least: This discussion is going nowhere. Correct. > >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
