Re: [RFC PATCH bpf-next 0/2] libbpf: Improve BPF load performance by selectively loading kmod BTFs

On Wed, Aug 5, 2026 at 9:21 PM Fuyu Zhao <[email protected]> wrote:
>
> Currently, during BPF object loading, load_module_btfs() unconditionally
> iterates over all loaded kernel modules and loads their BTFs. This
> introduces unnecessary overhead when a BPF program only needs a specific,
> small subset of modules. In environments with hundreds of modules,
> loading all module measurably increases the loading time.
>
> This series introduces a ".kmod_btfs" ELF section, allowing BPF programs
> to declare the modules that need BTF loading. libbpf parses this
> section, collects the module names, and skips loading BTFs for any
> module not in the list, thereby reducing overhead. It also stops the
> iteration early once all declared modules are found.
>
> Usage example:
>
>   DEFINE_KMOD_BTFS(_needed_kmods) = { "bpf_testmod" };
>
> Performance impact (<skel>__open_and_load() time):
>
>   Modules loaded | Without .kmod_btfs | With .kmod_btfs | Speedup
>   ---------------|--------------------|-----------------|--------
>   1              | 35.0 ms            | 35.0 ms         | Baseline
>   10             | 36.5 ms            | 35.1 ms         | +3.8%
>   100            | 46.2 ms            | 35.9 ms         | +22.3%
>   300            | 65.2 ms            | 38.0 ms         | +41.7%

First, is 30ms start up overhead really such a big deal when it comes
to one-time thing that sets up a bunch of BPF programs? Can you
elaborate on the use case you have that actually is harmed by this
libbpf behavior?

>
> Fuyu Zhao (2):
>   libbpf: support selective kernel module BTF loading via .kmod_btfs
>     section
>   selftests/bpf: add tests for selective kmod BTF loading
>
>  tools/lib/bpf/bpf_helpers.h                   |  14 +++
>  tools/lib/bpf/libbpf.c                        | 112 ++++++++++++++++++
>  .../selftests/bpf/prog_tests/kmod_btfs.c      |  47 ++++++++
>  tools/testing/selftests/bpf/progs/kmod_btfs.c |  14 +++
>  .../selftests/bpf/progs/kmod_btfs_mix.c       |  15 +++
>  .../selftests/bpf/progs/kmod_btfs_nonexist.c  |  17 +++
>  6 files changed, 219 insertions(+)
>  create mode 100644 tools/testing/selftests/bpf/prog_tests/kmod_btfs.c
>  create mode 100644 tools/testing/selftests/bpf/progs/kmod_btfs.c
>  create mode 100644 tools/testing/selftests/bpf/progs/kmod_btfs_mix.c
>  create mode 100644 tools/testing/selftests/bpf/progs/kmod_btfs_nonexist.c
>
> --
> 2.34.1
>
>