From: Jiri Olsa <jolsa@redhat.com>
To: Andrii Nakryiko <andrii.nakryiko@gmail.com>
Cc: Alexei Starovoitov <ast@kernel.org>,
Daniel Borkmann <daniel@iogearbox.net>,
Andrii Nakryiko <andrii@kernel.org>,
Networking <netdev@vger.kernel.org>, bpf <bpf@vger.kernel.org>,
Martin KaFai Lau <kafai@fb.com>, Song Liu <songliubraving@fb.com>,
Yonghong Song <yhs@fb.com>,
John Fastabend <john.fastabend@gmail.com>,
KP Singh <kpsingh@chromium.org>
Subject: Re: [RFC bpf-next 0/2] bpf: Fix BTF data for modules
Date: Tue, 26 Oct 2021 14:03:34 +0200 [thread overview]
Message-ID: <YXfulitQY1+Gd35h@krava> (raw)
In-Reply-To: <CAEf4BzbaD60KFsUB4VkTAH2v3+GFkRvRbY_O-bNSpNG0=8pJ0Q@mail.gmail.com>
On Mon, Oct 25, 2021 at 09:54:48PM -0700, Andrii Nakryiko wrote:
> On Sat, Oct 23, 2021 at 5:05 AM Jiri Olsa <jolsa@redhat.com> wrote:
> >
> > hi,
> > I'm trying to enable BTF for kernel module in fedora,
> > and I'm getting big increase on modules sizes on s390x arch.
> >
> > Size of modules in total - kernel dir under /lib/modules/VER/
> > from kernel-core and kernel-module packages:
> >
> > current new
> > aarch64 60M 76M
> > ppc64le 53M 66M
> > s390x 21M 41M
> > x86_64 64M 79M
> >
> > The reason for higher increase on s390x was that dedup algorithm
> > did not detect some of the big kernel structs like 'struct module',
> > so they are duplicated in the kernel module BTF data. The s390x
> > has many small modules that increased significantly in size because
> > of that even after compression.
> >
> > First issues was that the '--btf_gen_floats' option is not passed
> > to pahole for kernel module BTF generation.
> >
> > The other problem is more tricky and is the reason why this patchset
> > is RFC ;-)
> >
> > The s390x compiler generates multiple definitions of the same struct
> > and dedup algorithm does not seem to handle this at the moment.
> >
> > I put the debuginfo and btf dump of the s390x pnet.ko module in here:
> > http://people.redhat.com/~jolsa/kmodbtf/
> >
> > Please let me know if you'd like to see other info/files.
> >
>
> Hard to tell what's going on without vmlinux itself. Can you upload a
> corresponding kernel image with BTF in it?
sure, uploaded
jirka
>
> > I found code in dedup that seems to handle such situation for arrays,
> > and added 'some' fix for structs. With that change I can no longer
> > see vmlinux's structs in kernel module BTF data, but I have no idea
> > if that breaks anything else.
> >
> > thoughts? thanks,
> > jirka
> >
> >
> > ---
> > Jiri Olsa (2):
> > kbuild: Unify options for BTF generation for vmlinux and modules
> > bpf: Add support to detect and dedup instances of same structs
> >
> > Makefile | 3 +++
> > scripts/Makefile.modfinal | 2 +-
> > scripts/link-vmlinux.sh | 11 +----------
> > scripts/pahole-flags.sh | 20 ++++++++++++++++++++
> > tools/lib/bpf/btf.c | 12 ++++++++++--
> > 5 files changed, 35 insertions(+), 13 deletions(-)
> > create mode 100755 scripts/pahole-flags.sh
> >
>
next prev parent reply other threads:[~2021-10-26 12:03 UTC|newest]
Thread overview: 21+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-10-23 12:04 [RFC bpf-next 0/2] bpf: Fix BTF data for modules Jiri Olsa
2021-10-23 12:04 ` [PATCH bpf-next 1/2] kbuild: Unify options for BTF generation for vmlinux and modules Jiri Olsa
2021-10-26 4:56 ` Andrii Nakryiko
2021-10-26 12:03 ` Jiri Olsa
2021-10-23 12:04 ` [PATCH bpf-next 2/2] bpf: Add support to detect and dedup instances of same structs Jiri Olsa
2021-10-26 4:59 ` Andrii Nakryiko
2021-10-26 4:54 ` [RFC bpf-next 0/2] bpf: Fix BTF data for modules Andrii Nakryiko
2021-10-26 12:03 ` Jiri Olsa [this message]
2021-10-27 4:12 ` Andrii Nakryiko
2021-10-27 8:53 ` Jiri Olsa
2021-10-27 17:53 ` Andrii Nakryiko
2021-10-27 18:18 ` Jiri Olsa
2021-10-28 19:12 ` Jiri Olsa
2021-11-01 23:14 ` Andrii Nakryiko
2021-11-02 14:14 ` Jiri Olsa
2021-11-07 14:57 ` Jiri Olsa
2021-11-09 23:23 ` Andrii Nakryiko
2021-11-12 7:23 ` Jiri Olsa
2022-02-25 13:19 ` Alexander Egorenkov
2022-02-25 17:15 ` Jiri Olsa
2021-10-28 1:44 ` Kumar Kartikeya Dwivedi
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