linux-kernel - Re: [PATCHv4 bpf-next 0/5] bpf: Speed up symbol resolving in kprobe multi link

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Date:   Fri, 29 Apr 2022 07:28:11 -0700
From:   Andrii Nakryiko <andrii.nakryiko@...il.com>
To:     Jiri Olsa <jolsa@...nel.org>
Cc:     Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Andrii Nakryiko <andrii@...nel.org>,
        Masami Hiramatsu <mhiramat@...nel.org>,
        Networking <netdev@...r.kernel.org>, bpf <bpf@...r.kernel.org>,
        lkml <linux-kernel@...r.kernel.org>,
        Martin KaFai Lau <kafai@...com>,
        Song Liu <songliubraving@...com>, Yonghong Song <yhs@...com>,
        John Fastabend <john.fastabend@...il.com>,
        KP Singh <kpsingh@...omium.org>,
        Steven Rostedt <rostedt@...dmis.org>
Subject: Re: [PATCHv4 bpf-next 0/5] bpf: Speed up symbol resolving in kprobe
 multi link

On Thu, Apr 28, 2022 at 1:12 PM Jiri Olsa <jolsa@...nel.org> wrote:
>
> hi,
> sending additional fix for symbol resolving in kprobe multi link
> requested by Alexei and Andrii [1].
>
> This speeds up bpftrace kprobe attachment, when using pure symbols
> (3344 symbols) to attach:
>
> Before:
>
>   # perf stat -r 5 -e cycles ./src/bpftrace -e 'kprobe:x* {  } i:ms:1 { exit(); }'
>   ...
>   6.5681 +- 0.0225 seconds time elapsed  ( +-  0.34% )
>
> After:
>
>   # perf stat -r 5 -e cycles ./src/bpftrace -e 'kprobe:x* {  } i:ms:1 { exit(); }'
>   ...
>   0.5661 +- 0.0275 seconds time elapsed  ( +-  4.85% )
>
> v4 changes:
>   - fix compile issue [kernel test robot]
>   - added acks [Andrii]
>
> v3 changes:
>   - renamed kallsyms_lookup_names to ftrace_lookup_symbols
>     and moved it to ftrace.c [Masami]
>   - added ack [Andrii]
>   - couple small test fixes [Andrii]
>
> v2 changes (first version [2]):
>   - removed the 2 seconds check [Alexei]
>   - moving/forcing symbols sorting out of kallsyms_lookup_names function [Alexei]
>   - skipping one array allocation and copy_from_user [Andrii]
>   - several small fixes [Masami,Andrii]
>   - build fix [kernel test robot]
>
> thanks,
> jirka
>
>
> [1] https://lore.kernel.org/bpf/CAEf4BzZtQaiUxQ-sm_hH2qKPRaqGHyOfEsW96DxtBHRaKLoL3Q@mail.gmail.com/
> [2] https://lore.kernel.org/bpf/20220407125224.310255-1-jolsa@kernel.org/
> ---
> Jiri Olsa (5):
>       kallsyms: Fully export kallsyms_on_each_symbol function
>       ftrace: Add ftrace_lookup_symbols function
>       fprobe: Resolve symbols with ftrace_lookup_symbols
>       bpf: Resolve symbols with ftrace_lookup_symbols for kprobe multi link
>       selftests/bpf: Add attach bench test
>

Please check [0], it reports rcu_read_unlock() misuse

  [0] https://github.com/kernel-patches/bpf/runs/6223167405?check_suite_focus=true

>  include/linux/ftrace.h                                     |   6 ++++++
>  include/linux/kallsyms.h                                   |   7 ++++++-
>  kernel/kallsyms.c                                          |   3 +--
>  kernel/trace/bpf_trace.c                                   | 112 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++----------------------------------------------
>  kernel/trace/fprobe.c                                      |  32 ++++++++++++--------------------
>  kernel/trace/ftrace.c                                      |  62 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
>  tools/testing/selftests/bpf/prog_tests/kprobe_multi_test.c | 133 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
>  tools/testing/selftests/bpf/progs/kprobe_multi_empty.c     |  12 ++++++++++++
>  8 files changed, 298 insertions(+), 69 deletions(-)
>  create mode 100644 tools/testing/selftests/bpf/progs/kprobe_multi_empty.c