From: "Toke Høiland-Jørgensen" <firstname.lastname@example.org> To: John Fastabend <email@example.com>, Daniel Borkmann <firstname.lastname@example.org> Cc: Alexei Starovoitov <email@example.com>, Martin KaFai Lau <firstname.lastname@example.org>, Song Liu <email@example.com>, Yonghong Song <firstname.lastname@example.org>, Marek Majkowski <email@example.com>, Lorenz Bauer <firstname.lastname@example.org>, Alan Maguire <email@example.com>, Jesper Dangaard Brouer <firstname.lastname@example.org>, David Miller <email@example.com>, firstname.lastname@example.org, email@example.com Subject: RE: [PATCH bpf-next v3 0/5] xdp: Support multiple programs on a single interface through chain calls Date: Tue, 08 Oct 2019 10:42:00 +0200 [thread overview] Message-ID: <firstname.lastname@example.org> (raw) In-Reply-To: <5d9b8ac5655_2a4b2aed075a45b41@john-XPS-13-9370.notmuch> John Fastabend <email@example.com> writes: > Toke Høiland-Jørgensen wrote: >> This series adds support for executing multiple XDP programs on a single >> interface in sequence, through the use of chain calls, as discussed at the Linux >> Plumbers Conference last month: >> >> https://linuxplumbersconf.org/event/4/contributions/460/ >> > > Can we add RFC to the title if we are just iterating through > idea-space here. I don't view this as "just iterating through idea-space". I'll admit that I may have overestimated the extent to which we were all on the same page on this after LPC, but I do view these submissions as serious proposals that are making progress... :) >> # HIGH-LEVEL IDEA >> >> Since Alexei pointed out some issues with trying to rewrite the eBPF byte code, >> let's try a third approach: We add the ability to chain call programs into the >> eBPF execution core itself, but without rewriting the eBPF byte code. >> >> As in the previous version, the bpf() syscall gets a couple of new commands >> which takes a pair of BPF program fds and a return code. It will then attach the >> second program to the first one in a structured keyed by return code. When a >> program chain is thus established, the former program will tail call to the >> latter at the end of its execution. >> >> The actual tail calling is achieved by adding a new flag to struct bpf_prog and >> having BPF_PROG_RUN run the chain call logic if that flag is set. This means >> that if the feature is *not* used, the overhead is a single conditional branch >> (which means I couldn't measure a performance difference, as can be seen in the >> results below). >> > > I still believe user space should be able to link these multiple > programs together as Ed and I were suggesting in the last series. I expect that userspace probably could (I mean, after all, eBPF is within spitting distance of a full almost-Turing-complete executing environment so userspace can conceivably do pretty much anything). However, I don't believe that doing it in userspace is the best solution. I view it as a tradeoff: How much complexity do we have to add to the kernel to make things easier for userspace. And given that we can do this without negatively impacting performance, and with a reasonable cost in terms of complexity (both of which I think this series demonstrates that yes, we can), I think this makes sense to put in the kernel. > Also by doing it by linking your control program can be arbitrary > complex. For example not just taking the output of one program and > jumping to another but doing arbitrary more complex/interesting > things. Taking the input from multiple programs to pick next call for > example. I expect there will indeed be more complex use cases where combining multiple programs in arbitrary complex ways would make a lot of sense, and doing that by linking in userspace is probably a good fit for that. But for the simple use case of running multiple programs after one another, I think it is overkill, and something that is better to do in the kernel. -Toke
prev parent reply other threads:[~2019-10-08 8:42 UTC|newest] Thread overview: 55+ messages / expand[flat|nested] mbox.gz Atom feed top 2019-10-07 17:20 Toke Høiland-Jørgensen 2019-10-07 17:20 ` [PATCH bpf-next v3 1/5] bpf: Support chain calling multiple BPF programs after each other Toke Høiland-Jørgensen 2019-10-07 20:42 ` Alexei Starovoitov 2019-10-08 8:07 ` Toke Høiland-Jørgensen 2019-10-09 1:51 ` Alexei Starovoitov 2019-10-09 8:03 ` Toke Høiland-Jørgensen 2019-10-10 4:41 ` Alexei Starovoitov 2019-10-14 12:35 ` Toke Høiland-Jørgensen 2019-10-14 17:08 ` John Fastabend 2019-10-14 18:48 ` Toke Høiland-Jørgensen 2019-10-15 16:30 ` Edward Cree 2019-10-15 16:42 ` Toke Høiland-Jørgensen 2019-10-15 18:33 ` Edward Cree 2019-10-17 12:11 ` Toke Høiland-Jørgensen 2019-10-22 17:27 ` Edward Cree 2019-10-22 18:07 ` Toke Høiland-Jørgensen 2019-11-12 2:51 ` static and dynamic linking. Was: [PATCH bpf-next v3 1/5] bpf: Support chain calling multiple BPF Alexei Starovoitov 2019-11-12 16:20 ` Toke Høiland-Jørgensen 2019-11-12 19:52 ` Alexei Starovoitov 2019-11-12 21:25 ` Edward Cree 2019-11-12 23:18 ` Alexei Starovoitov 2019-11-13 18:30 ` Edward Cree 2019-11-13 18:51 ` Andrii Nakryiko 2019-11-15 2:13 ` Alexei Starovoitov 2019-11-15 16:56 ` John Fastabend 2019-11-12 23:25 ` John Fastabend 2019-11-13 0:21 ` Alexei Starovoitov 2019-11-13 5:33 ` John Fastabend 2019-11-15 1:50 ` Alexei Starovoitov 2019-11-15 16:39 ` John Fastabend 2019-11-14 15:41 ` Toke Høiland-Jørgensen 2019-11-12 16:32 ` Edward Cree 2019-11-15 11:48 ` Lorenz Bauer 2019-11-15 23:02 ` Alexei Starovoitov 2019-11-18 13:29 ` Lorenz Bauer 2019-10-21 23:51 ` [PATCH bpf-next v3 1/5] bpf: Support chain calling multiple BPF programs after each other Edward Cree 2019-10-16 2:28 ` Alexei Starovoitov 2019-10-16 8:27 ` Jesper Dangaard Brouer 2019-10-16 10:35 ` Daniel Borkmann 2019-10-16 11:16 ` Toke Høiland-Jørgensen 2019-10-16 13:51 ` Toke Høiland-Jørgensen 2019-10-19 20:09 ` bpf indirect calls Alexei Starovoitov 2019-10-20 10:58 ` Toke Høiland-Jørgensen 2019-10-25 16:30 ` Alexei Starovoitov 2019-10-27 12:15 ` Toke Høiland-Jørgensen 2019-10-09 10:19 ` [PATCH bpf-next v3 1/5] bpf: Support chain calling multiple BPF programs after each other Jesper Dangaard Brouer 2019-10-09 17:57 ` Alexei Starovoitov 2019-10-07 17:20 ` [PATCH bpf-next v3 2/5] bpf: Add support for setting chain call sequence for programs Toke Høiland-Jørgensen 2019-10-07 20:38 ` Daniel Borkmann 2019-10-08 8:09 ` Toke Høiland-Jørgensen 2019-10-07 17:20 ` [PATCH bpf-next v3 3/5] tools: Update bpf.h header for program chain calls Toke Høiland-Jørgensen 2019-10-07 17:20 ` [PATCH bpf-next v3 4/5] libbpf: Add syscall wrappers for BPF_PROG_CHAIN_* commands Toke Høiland-Jørgensen 2019-10-07 17:20 ` [PATCH bpf-next v3 5/5] selftests: Add tests for XDP chain calls Toke Høiland-Jørgensen 2019-10-07 18:58 ` [PATCH bpf-next v3 0/5] xdp: Support multiple programs on a single interface through " John Fastabend 2019-10-08 8:42 ` Toke Høiland-Jørgensen [this message]
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