Re: [PATCH bpf-next v9 08/10] bpf: Skip anonymous types in type lookup for performance

[Donglin Peng]

On Mon, Dec 8, 2025 at 2:24 PM Donglin Peng <dolinux.peng@xxxxxxxxx> wrote:
>
> From: pengdonglin <pengdonglin@xxxxxxxxxx>
>
> Currently, vmlinux and kernel module BTFs are unconditionally
> sorted during the build phase, with named types placed at the
> end. Thus, anonymous types should be skipped when starting the
> search. In my vmlinux BTF, the number of anonymous types is
> 61,747, which means the loop count can be reduced by 61,747.
>
> Cc: Eduard Zingerman <eddyz87@xxxxxxxxx>
> Cc: Alexei Starovoitov <ast@xxxxxxxxxx>
> Cc: Andrii Nakryiko <andrii.nakryiko@xxxxxxxxx>
> Cc: Alan Maguire <alan.maguire@xxxxxxxxxx>
> Cc: Ihor Solodrai <ihor.solodrai@xxxxxxxxx>
> Cc: Xiaoqin Zhang <zhangxiaoqin@xxxxxxxxxx>
> Signed-off-by: pengdonglin <pengdonglin@xxxxxxxxxx>
> ---
>  include/linux/btf.h   |  1 +
>  kernel/bpf/btf.c      | 15 ++++++++++-----
>  kernel/bpf/verifier.c |  7 +------
>  3 files changed, 12 insertions(+), 11 deletions(-)
>
> diff --git a/include/linux/btf.h b/include/linux/btf.h
> index f06976ffb63f..2d28f2b22ae5 100644
> --- a/include/linux/btf.h
> +++ b/include/linux/btf.h
> @@ -220,6 +220,7 @@ bool btf_is_module(const struct btf *btf);
>  bool btf_is_vmlinux(const struct btf *btf);
>  struct module *btf_try_get_module(const struct btf *btf);
>  u32 btf_nr_types(const struct btf *btf);
> +u32 btf_sorted_start_id(const struct btf *btf);
>  struct btf *btf_base_btf(const struct btf *btf);
>  bool btf_type_is_i32(const struct btf_type *t);
>  bool btf_type_is_i64(const struct btf_type *t);
> diff --git a/kernel/bpf/btf.c b/kernel/bpf/btf.c
> index 925cb524f3a8..5f4f51b0acf4 100644
> --- a/kernel/bpf/btf.c
> +++ b/kernel/bpf/btf.c
> @@ -550,6 +550,11 @@ u32 btf_nr_types(const struct btf *btf)
>         return total;
>  }
>
> +u32 btf_sorted_start_id(const struct btf *btf)
> +{
> +       return btf->sorted_start_id ?: (btf->start_id ?: 1);
> +}
> +
>  /*
>   * Assuming that types are sorted by name in ascending order.
>   */
> @@ -3540,9 +3545,9 @@ const char *btf_find_decl_tag_value(const struct btf *btf, const struct btf_type
>  {
>         const char *value = NULL;
>         const struct btf_type *t;
> -       int len, id;
> +       int len, id = btf->sorted_start_id > 0 ? btf->sorted_start_id - 1 : 0;
>
> -       id = btf_find_next_decl_tag(btf, pt, comp_idx, tag_key, 0);
> +       id = btf_find_next_decl_tag(btf, pt, comp_idx, tag_key, id);

Sorry, we should pass the sorted_start_id of the base BTF.

>         if (id < 0)
>                 return ERR_PTR(id);
>
> @@ -7859,7 +7864,7 @@ int btf_prepare_func_args(struct bpf_verifier_env *env, int subprog)
>          */
>         for (i = 0; i < nargs; i++) {
>                 u32 tags = 0;
> -               int id = 0;
> +               int id = btf->sorted_start_id > 0 ? btf->sorted_start_id - 1 : 0;

Ditto.

>
>                 /* 'arg:<tag>' decl_tag takes precedence over derivation of
>                  * register type from BTF type itself
> @@ -9340,7 +9345,7 @@ bpf_core_find_cands(struct bpf_core_ctx *ctx, u32 local_type_id)
>         }
>
>         /* Attempt to find target candidates in vmlinux BTF first */
> -       cands = bpf_core_add_cands(cands, main_btf, 1);
> +       cands = bpf_core_add_cands(cands, main_btf, main_btf->sorted_start_id);

Invoke btf_sorted_start_id.

>         if (IS_ERR(cands))
>                 return ERR_CAST(cands);
>
> @@ -9372,7 +9377,7 @@ bpf_core_find_cands(struct bpf_core_ctx *ctx, u32 local_type_id)
>                  */
>                 btf_get(mod_btf);
>                 spin_unlock_bh(&btf_idr_lock);
> -               cands = bpf_core_add_cands(cands, mod_btf, btf_nr_types(main_btf));
> +               cands = bpf_core_add_cands(cands, mod_btf, mod_btf->sorted_start_id);
>                 btf_put(mod_btf);
>                 if (IS_ERR(cands))
>                         return ERR_CAST(cands);
> diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
> index f0ca69f888fa..2ae87075db6a 100644
> --- a/kernel/bpf/verifier.c
> +++ b/kernel/bpf/verifier.c
> @@ -20655,12 +20655,7 @@ static int find_btf_percpu_datasec(struct btf *btf)
>          * types to look at only module's own BTF types.
>          */
>         n = btf_nr_types(btf);
> -       if (btf_is_module(btf))
> -               i = btf_nr_types(btf_vmlinux);
> -       else
> -               i = 1;
> -
> -       for(; i < n; i++) {
> +       for (i = btf_sorted_start_id(btf); i < n; i++) {
>                 t = btf_type_by_id(btf, i);
>                 if (BTF_INFO_KIND(t->info) != BTF_KIND_DATASEC)
>                         continue;
> --
> 2.34.1
>