linux-kernel - Re: [PATCH bpf-next v12 04/11] libbpf: Optimize type lookup with binary search for sorted BTF

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Message-ID: <CAEf4BzZkNdZuSWb+G98LDSn3gL22p+g7-dHqFVH6jcqUsrKYVA@mail.gmail.com>
Date: Tue, 13 Jan 2026 16:29:35 -0800
From: Andrii Nakryiko <andrii.nakryiko@...il.com>
To: Donglin Peng <dolinux.peng@...il.com>
Cc: ast@...nel.org, eddyz87@...il.com, zhangxiaoqin@...omi.com, 
	ihor.solodrai@...ux.dev, linux-kernel@...r.kernel.org, bpf@...r.kernel.org, 
	Donglin Peng <pengdonglin@...omi.com>, Alan Maguire <alan.maguire@...cle.com>
Subject: Re: [PATCH bpf-next v12 04/11] libbpf: Optimize type lookup with
 binary search for sorted BTF

On Fri, Jan 9, 2026 at 5:00 AM Donglin Peng <dolinux.peng@...il.com> wrote:
>
> From: Donglin Peng <pengdonglin@...omi.com>
>
> This patch introduces binary search optimization for BTF type lookups
> when the BTF instance contains sorted types.
>
> The optimization significantly improves performance when searching for
> types in large BTF instances with sorted types. For unsorted BTF, the
> implementation falls back to the original linear search.
>
> Cc: Eduard Zingerman <eddyz87@...il.com>
> Cc: Alexei Starovoitov <ast@...nel.org>
> Cc: Andrii Nakryiko <andrii.nakryiko@...il.com>
> Cc: Alan Maguire <alan.maguire@...cle.com>
> Cc: Ihor Solodrai <ihor.solodrai@...ux.dev>
> Cc: Xiaoqin Zhang <zhangxiaoqin@...omi.com>
> Signed-off-by: Donglin Peng <pengdonglin@...omi.com>
> ---
>  tools/lib/bpf/btf.c | 90 +++++++++++++++++++++++++++++++++------------
>  1 file changed, 66 insertions(+), 24 deletions(-)
>

[...]

>  static __s32 btf_find_by_name_kind(const struct btf *btf, int start_id,
> -                                  const char *type_name, __u32 kind)
> +                                  const char *type_name, __s32 kind)
>  {
> -       __u32 i, nr_types = btf__type_cnt(btf);
> +       const struct btf_type *t;
> +       const char *tname;
> +       __s32 idx;
> +
> +       if (start_id < btf->start_id) {
> +               idx = btf_find_by_name_kind(btf->base_btf, start_id,
> +                                           type_name, kind);
> +               if (idx >= 0)
> +                       return idx;
> +               start_id = btf->start_id;
> +       }
>
> -       if (kind == BTF_KIND_UNKN || !strcmp(type_name, "void"))
> +       if (kind == BTF_KIND_UNKN || strcmp(type_name, "void") == 0)
>                 return 0;
>
> -       for (i = start_id; i < nr_types; i++) {
> -               const struct btf_type *t = btf__type_by_id(btf, i);
> -               const char *name;
> +       if (btf->named_start_id > 0 && type_name[0]) {
> +               start_id = max(start_id, btf->named_start_id);
> +               idx = btf_find_type_by_name_bsearch(btf, type_name, start_id);
> +               for (; idx < btf__type_cnt(btf); idx++) {

I hope the compiler will optimize out btf__type_cnt() and won't be
recalculating it all the time, but I'd absolutely make sure by keeping
nr_types local variable which you deleted for some reason. Please
include in your follow up.

> +                       t = btf__type_by_id(btf, idx);
> +                       tname = btf__str_by_offset(btf, t->name_off);
> +                       if (strcmp(tname, type_name) != 0)
> +                               return libbpf_err(-ENOENT);
> +                       if (kind < 0 || btf_kind(t) == kind)
> +                               return idx;
> +               }
> +       } else {
> +               __u32 i, total;
>
> -               if (btf_kind(t) != kind)
> -                       continue;
> -               name = btf__name_by_offset(btf, t->name_off);
> -               if (name && !strcmp(type_name, name))
> -                       return i;
> +               total = btf__type_cnt(btf);

and here you have a local total pre-calculated. Just move it outside
of this if/else and use in both branches

(I adjusted this trivially while applying, also unified idx,i -> id


> +               for (i = start_id; i < total; i++) {
> +                       t = btf_type_by_id(btf, i);
> +                       if (kind > 0 && btf_kind(t) != kind)
> +                               continue;
> +                       tname = btf__str_by_offset(btf, t->name_off);
> +                       if (strcmp(tname, type_name) == 0)
> +                               return i;
> +               }
>         }
>

[...]