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From: "Toke Høiland-Jørgensen" <toke@redhat.com>
To: Daniel Borkmann <daniel@iogearbox.net>,
	John Fastabend <john.fastabend@gmail.com>
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>,
	David Miller <davem@davemloft.net>,
	Jesper Dangaard Brouer <brouer@redhat.com>,
	netdev@vger.kernel.org, bpf@vger.kernel.org
Subject: Re: [PATCH bpf-next 0/9] xdp: Support multiple programs on a single interface through chain calls
Date: Wed, 02 Oct 2019 21:29:35 +0200	[thread overview]
Message-ID: <87o8yzq734.fsf@toke.dk> (raw)
In-Reply-To: <20191002191522.GA9196@pc-66.home>

Daniel Borkmann <daniel@iogearbox.net> writes:

> On Wed, Oct 02, 2019 at 09:43:49AM -0700, John Fastabend wrote:
>> 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/
>> > 
>> > # HIGH-LEVEL IDEA
>> > 
>> > The basic idea is to express the chain call sequence through a special map type,
>> > which contains a mapping from a (program, return code) tuple to another program
>> > to run in next in the sequence. Userspace can populate this map to express
>> > arbitrary call sequences, and update the sequence by updating or replacing the
>> > map.
>> > 
>> > The actual execution of the program sequence is done in bpf_prog_run_xdp(),
>> > which will lookup the chain sequence map, and if found, will loop through calls
>> > to BPF_PROG_RUN, looking up the next XDP program in the sequence based on the
>> > previous program ID and return code.
>> > 
>> > An XDP chain call map can be installed on an interface by means of a new netlink
>> > attribute containing an fd pointing to a chain call map. This can be supplied
>> > along with the XDP prog fd, so that a chain map is always installed together
>> > with an XDP program.
>> > 
>> > # PERFORMANCE
>> > 
>> > I performed a simple performance test to get an initial feel for the overhead of
>> > the chain call mechanism. This test consists of running only two programs in
>> > sequence: One that returns XDP_PASS and another that returns XDP_DROP. I then
>> > measure the drop PPS performance and compare it to a baseline of just a single
>> > program that only returns XDP_DROP.
>> > 
>> > For comparison, a test case that uses regular eBPF tail calls to sequence two
>> > programs together is also included. Finally, because 'perf' showed that the
>> > hashmap lookup was the largest single source of overhead, I also added a test
>> > case where I removed the jhash() call from the hashmap code, and just use the
>> > u32 key directly as an index into the hash bucket structure.
>> > 
>> > The performance for these different cases is as follows (with retpolines disabled):
>> 
>> retpolines enabled would also be interesting.
>> 
>> > 
>> > | Test case                       | Perf      | Add. overhead | Total overhead |
>> > |---------------------------------+-----------+---------------+----------------|
>> > | Before patch (XDP DROP program) | 31.0 Mpps |               |                |
>> > | After patch (XDP DROP program)  | 28.9 Mpps |        2.3 ns |         2.3 ns |
>> 
>> IMO even 1 Mpps overhead is too much for a feature that is primarily about
>> ease of use. Sacrificing performance to make userland a bit easier is hard
>> to justify for me when XDP _is_ singularly about performance. Also that is
>> nearly 10% overhead which is fairly large. So I think going forward the
>> performance gab needs to be removed.
>
> Fully agree, for the case where this facility is not used, it must
> have *zero* overhead. This is /one/ map flavor, in future there will
> be other facilities with different use-cases, but we cannot place them
> all into the critical fast-path. Given this is BPF, we have the
> flexibility that this can be hidden behind the scenes by rewriting and
> therefore only add overhead when used.
>
> What I also see as a red flag with this proposal is the fact that it's
> tied to XDP only because you need to go and hack bpf_prog_run_xdp()
> all the way to fetch xdp->rxq->dev->xdp_chain_map even though the
> map/concept itself is rather generic and could be used in various
> other program types as well. I'm very sure that once there, people
> would request it. Therefore, better to explore a way where this has no
> changes to BPF_PROG_RUN() similar to the original tail call work.

As I said in the other reply, I actually went out of my way to make this
XDP only. But since you're now the third person requesting it not be, I
guess I'll take the hint and look at a more general way to hook this in :)

-Toke

  reply	other threads:[~2019-10-02 19:29 UTC|newest]

Thread overview: 53+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-10-02 13:30 [PATCH bpf-next 0/9] xdp: Support multiple programs on a single interface through chain calls Toke Høiland-Jørgensen
2019-10-02 13:30 ` [PATCH bpf-next 1/9] hashtab: Add new bpf_map_fd_put_value op Toke Høiland-Jørgensen
2019-10-02 13:30 ` [PATCH bpf-next 2/9] xdp: Add new xdp_chain_map type for specifying XDP call sequences Toke Høiland-Jørgensen
2019-10-02 15:50   ` Lorenz Bauer
2019-10-02 18:25     ` Toke Høiland-Jørgensen
2019-10-02 13:30 ` [PATCH bpf-next 3/9] xdp: Support setting and getting device chain map Toke Høiland-Jørgensen
2019-10-02 15:50   ` Lorenz Bauer
2019-10-02 18:32     ` Toke Høiland-Jørgensen
2019-10-02 18:07   ` kbuild test robot
2019-10-02 18:29   ` kbuild test robot
2019-10-02 13:30 ` [PATCH bpf-next 4/9] xdp: Implement chain call logic to support multiple programs on one interface Toke Høiland-Jørgensen
2019-10-02 17:33   ` kbuild test robot
2019-10-02 17:53   ` kbuild test robot
2019-10-02 13:30 ` [PATCH bpf-next 5/9] tools/include/uapi: Add XDP chain map definitions Toke Høiland-Jørgensen
2019-10-02 13:30 ` [PATCH bpf-next 6/9] tools/libbpf_probes: Add support for xdp_chain map type Toke Høiland-Jørgensen
2019-10-02 13:30 ` [PATCH bpf-next 7/9] bpftool: Add definitions " Toke Høiland-Jørgensen
2019-10-02 13:30 ` [PATCH bpf-next 8/9] libbpf: Add support for setting and getting XDP chain maps Toke Høiland-Jørgensen
2019-10-02 13:30 ` [PATCH bpf-next 9/9] selftests: Add tests for XDP chain calls Toke Høiland-Jørgensen
2019-10-02 15:10 ` [PATCH bpf-next 0/9] xdp: Support multiple programs on a single interface through " Alan Maguire
2019-10-02 15:33   ` Toke Høiland-Jørgensen
2019-10-02 16:34     ` John Fastabend
2019-10-02 18:33       ` Toke Høiland-Jørgensen
2019-10-02 20:34         ` John Fastabend
2019-10-03  7:48           ` Toke Høiland-Jørgensen
2019-10-03 10:09             ` Jesper Dangaard Brouer
2019-10-03 19:45               ` John Fastabend
2019-10-02 16:35 ` Lorenz Bauer
2019-10-02 18:54   ` Toke Høiland-Jørgensen
2019-10-02 16:43 ` John Fastabend
2019-10-02 19:09   ` Toke Høiland-Jørgensen
2019-10-02 19:15   ` Daniel Borkmann
2019-10-02 19:29     ` Toke Høiland-Jørgensen [this message]
2019-10-02 19:46     ` Alexei Starovoitov
2019-10-03  7:58       ` Toke Høiland-Jørgensen
2019-10-02 18:38 ` Song Liu
2019-10-02 18:54   ` Song Liu
2019-10-02 19:25     ` Toke Høiland-Jørgensen
2019-10-03  8:53       ` Jesper Dangaard Brouer
2019-10-03 14:03         ` Alexei Starovoitov
2019-10-03 14:33           ` Toke Høiland-Jørgensen
2019-10-03 14:53             ` Edward Cree
2019-10-03 18:49               ` Jesper Dangaard Brouer
2019-10-03 19:35               ` John Fastabend
2019-10-04  8:09                 ` Toke Høiland-Jørgensen
2019-10-04 10:34                   ` Edward Cree
2019-10-04 15:58                     ` Lorenz Bauer
2019-10-07 16:43                       ` Edward Cree
2019-10-07 17:12                         ` Lorenz Bauer
2019-10-07 19:21                           ` Edward Cree
2019-10-07 21:01                         ` Alexei Starovoitov
2019-10-02 19:23   ` Toke Høiland-Jørgensen
2019-10-02 19:49     ` Song Liu
2019-10-03  7:59       ` Toke Høiland-Jørgensen

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