linux-kernel - Re: [PATCH bpf-next v10 08/13] bpf: Skip anonymous types in type lookup for performance

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Message-ID: <CAErzpmvskuQrs=+=TydAsQRe99rqb=539eBOfvd3eJpEgxfwWw@mail.gmail.com>
Date: Fri, 19 Dec 2025 13:40:34 +0800
From: Donglin Peng <dolinux.peng@...il.com>
To: Andrii Nakryiko <andrii.nakryiko@...il.com>
Cc: Eduard Zingerman <eddyz87@...il.com>, ast@...nel.org, zhangxiaoqin@...omi.com, 
	ihor.solodrai@...ux.dev, linux-kernel@...r.kernel.org, bpf@...r.kernel.org, 
	pengdonglin <pengdonglin@...omi.com>, Alan Maguire <alan.maguire@...cle.com>
Subject: Re: [PATCH bpf-next v10 08/13] bpf: Skip anonymous types in type
 lookup for performance

On Fri, Dec 19, 2025 at 7:59 AM Andrii Nakryiko
<andrii.nakryiko@...il.com> wrote:
>
> On Thu, Dec 18, 2025 at 2:21 PM Eduard Zingerman <eddyz87@...il.com> wrote:
> >
> > On Thu, 2025-12-18 at 19:30 +0800, Donglin Peng wrote:
> > > From: pengdonglin <pengdonglin@...omi.com>
> > >
> > > 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@...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: pengdonglin <pengdonglin@...omi.com>
> > > ---
> >
> > Acked-by: Eduard Zingerman <eddyz87@...il.com>
> >
> > >  include/linux/btf.h   |  1 +
> > >  kernel/bpf/btf.c      | 24 ++++++++++++++++++++----
> > >  kernel/bpf/verifier.c |  7 +------
> > >  3 files changed, 22 insertions(+), 10 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 a9e2345558c0..3aeb4f00cbfe 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)
> >
> > Nit: the name is a bit confusing, given that it not always returns the
> >      start id for sorted part. btf_maybe_first_named_id?
> >      Can't figure out a good name :(
>
> yeah, I agree, it is quite confusing overall. I think we should at
> least add comments why we start with something different than 1 in
> those few places where we use this optimization...

Thanks, I will add comments to make it more clear.

>
> let's name it btf_named_start_id() and specify in the comment that for
> non-sorted BTFs we conservatively fallback to the first type.

Thanks, I will do it.

>
> btw, maybe it would be good to have two versions of this (or bool
> flag,but we all hate bool flags) to either return own start id (i.e.,
> ignoring base BTF) or recursively go down to the base BTF.

Thanks, I will implement it.

>
> Having that
>
> while (base_btf->base_btf)
>     base_btf = base_btf->base_btf;
>
> logic in a few places looks a bit too low-level and distracting, IMO.

Agreed.

>
> >
> > > +{
> > > +     return btf->sorted_start_id ?: (btf->start_id ?: 1);
> > > +}
> > > +
> > >  /*
> > >   * Assuming that types are sorted by name in ascending order.
> > >   */
> >
> > [...]