linux-kernel - Re: [RFC PATCH v7 5/7] libbpf: Implement BTF type sorting validation for binary search optimization

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Message-ID: <CAErzpmv-CQy42LMFR4hzD4ANqL4ENnWyb0uKr7_FH1fj98S2QA@mail.gmail.com>
Date: Sat, 22 Nov 2025 23:45:52 +0800
From: Donglin Peng <dolinux.peng@...il.com>
To: Eduard Zingerman <eddyz87@...il.com>
Cc: Andrii Nakryiko <andrii.nakryiko@...il.com>, ast@...nel.org, zhangxiaoqin@...omi.com, 
	linux-kernel@...r.kernel.org, bpf@...r.kernel.org, 
	Donglin Peng <pengdonglin@...omi.com>, Alan Maguire <alan.maguire@...cle.com>, 
	Song Liu <song@...nel.org>
Subject: Re: [RFC PATCH v7 5/7] libbpf: Implement BTF type sorting validation
 for binary search optimization

On Sat, Nov 22, 2025 at 5:05 PM Eduard Zingerman <eddyz87@...il.com> wrote:
>
> On Sat, 2025-11-22 at 00:50 -0800, Eduard Zingerman wrote:
>
> [...]
>
> > > Thanks. I’ve looked into find_btf_percpu_datasec and we can’t use
> > > btf_find_by_name_kind here because the search scope differs. For
> > > a module BTF, find_btf_percpu_datasec only searches within the
> > > module’s own BTF, whereas btf_find_by_name_kind prioritizes
> > > searching the base BTF first. Thus, placing named types ahead is
> > > more effective here. Besides, I found that the '.data..percpu' named
> > > type will be placed at [1] for vmlinux BTF because the prefix '.' is
> > > smaller than any letter, so the linear search only requires one loop to
> > > locate it. However, if we put named types at the end, it will need more
> > > than 60,000 loops..
> >
> > But this can be easily fixed if a variant of btf_find_by_name_kind()
> > is provided that looks for a match only in a specific BTF. Or accepts
> > a start id parameter.
>
> Also, I double checked, and for my vmlinux the id for '.data..percpu'
> section is 110864, the last id of all. So, having all anonymous types
> in front does not change status-quo compared to current implementation.

Yes. If types are sorted alphabetically, the '.data..percpu' section will
have ID 1 in vmlinux BTF. In this case, linear search performance is
optimal when named types are placed ahead of anonymous types.

I would like to understand the benefits of having anonymous types at the
front of named types.