From: "Toke Høiland-Jørgensen" <toke@redhat.com>
To: John Fastabend <john.fastabend@gmail.com>,
Daniel Borkmann <daniel@iogearbox.net>
Cc: Alexei Starovoitov <ast@kernel.org>,
Martin KaFai Lau <kafai@fb.com>, Song Liu <songliubraving@fb.com>,
Yonghong Song <yhs@fb.com>,
Marek Majkowski <marek@cloudflare.com>,
Lorenz Bauer <lmb@cloudflare.com>,
Alan Maguire <alan.maguire@oracle.com>,
Jesper Dangaard Brouer <brouer@redhat.com>,
David Miller <davem@davemloft.net>,
netdev@vger.kernel.org, bpf@vger.kernel.org
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: <87h84jljc7.fsf@toke.dk> (raw)
In-Reply-To: <5d9b8ac5655_2a4b2aed075a45b41@john-XPS-13-9370.notmuch>
John Fastabend <john.fastabend@gmail.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: 61+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-10-07 17:20 [PATCH bpf-next v3 0/5] xdp: Support multiple programs on a single interface through chain calls 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
2023-09-27 13:27 ` Matt Bobrowski
2023-09-29 21:06 ` Alexei Starovoitov
2023-10-02 18:50 ` Barret Rhoden
2023-10-06 9:36 ` Matt Bobrowski
2023-10-06 18:49 ` Alexei Starovoitov
2023-10-19 12:28 ` Matt Bobrowski
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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