netdev - Re: call for bpf progs. Re: [PATCHv2 bpf-next 5/5] selftests: bpf: add test for sk

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Message-ID: <CAEf4BzZZfsW-xw8AtmwA4gSBusrBW8M6D4RLqO3SWV_0DQxW8w@mail.gmail.com>
Date:   Fri, 27 Mar 2020 17:17:38 -0700
From:   Andrii Nakryiko <andrii.nakryiko@...il.com>
To:     Joe Stringer <joe@...d.net.nz>
Cc:     Alexei Starovoitov <alexei.starovoitov@...il.com>,
        Lorenz Bauer <lmb@...udflare.com>, Yonghong Song <yhs@...com>,
        bpf <bpf@...r.kernel.org>, Networking <netdev@...r.kernel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Alexei Starovoitov <ast@...nel.org>,
        Eric Dumazet <eric.dumazet@...il.com>,
        Martin Lau <kafai@...com>,
        john fastabend <john.fastabend@...il.com>
Subject: Re: call for bpf progs. Re: [PATCHv2 bpf-next 5/5] selftests: bpf:
 add test for sk_assign

On Fri, Mar 27, 2020 at 12:07 PM Joe Stringer <joe@...d.net.nz> wrote:
>
> On Thu, Mar 26, 2020 at 2:07 PM Alexei Starovoitov
> <alexei.starovoitov@...il.com> wrote:
> > The second concern was pruning, but iirc the experiments were inconclusive.
> > selftests/bpf only has old fb progs. Hence, I think, the step zero is for
> > everyone to contribute their bpf programs written in C. If we have both
> > cilium and cloudflare progs as selftests it will help a lot to guide such long
> > lasting verifier decisions.
>
> How would you like to handle program changes over time for this?
>
> In Cilium community we periodically rebuild bpf-next VM images for
> testing, and run every pull request against those images[0]. We also
> test against specific older kernels, currently 4.9 and 4.19. This
> allows us to get some sense for the impact of upstream changes while
> developing Cilium features, but unfortunately doesn't allow everyone
> using kernel selftests to get that feedback at least from the kernel
> tree. We also have a verifier complexity test script where we compile
> with the maximum number of features (to ideally generate the most
> complex programs possible) then attempt to load all of the various
> programs, and output the complexity count that the kernel reports[1,2]
> which we can track over time.
>
> However Cilium BPF programs are actively developing and even if we
> merge these programs into the kernel tree, they will get out-of-date
> quickly. Up until recently everything was verifying fine compiling
> with LLVM7 and loading into bpf-next. Over the past month we started
> noticing new issues not with the existing implementation, but in *new*
> BPF features. As we increased complexity, our CI started failing
> against bpf-next[3] while they loaded fine on older kernels. We ended
> up mitigating by upgrading to LLVM-10. Long story short, there's
> several moving parts; changing BPF program implementations, changing
> the compiler toolchain, changing the kernel verifier. So my question
> is basically, where's the line of responsibility for what the kernel
> selftests are responsible for vs integration tests? How do we maintain
> those over time as the BPF programs and compiler changes?

Just wanted to point out that libbpf's Github CI has multi-kernel
testing, so we'll be able to capture regressions on old kernels that
are caused by libbpf and/or nightly clang (we are currently pulling
clang-11 from nightly packages). We are also testing against latest
kernel as well, so if they break, we'll need to fix them. Which is why
I'd like those programs to be manageable in size and complexity and a
simple part of test_progs, not in some Docker container :)

>
> Do we just parachute the ~11K LoC of Cilium datapath into the kernel
> tree once per cycle? Or should Cilium autobuild a verifier-test docker
> image that kernel testing scripts can pull & run? Or would it be
> helpful to have a separate GitHub project similar to libbpf that pulls
> out kernel selftests, Cilium progs, fb progs, cloudflare progs, etc
> automatically and centralizes a generic suite of BPF verifier
> integration tests? Some other option?
>
> [0] https://github.com/cilium/packer-ci-build
> [1] https://github.com/cilium/cilium/blob/master/test/bpf/check-complexity.sh
> [2] https://github.com/cilium/cilium/blob/master/test/bpf/verifier-test.sh
> [3] https://github.com/cilium/cilium/issues/10517