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

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Message-ID: <ce92f733d24bfad103a9abcc209f411398e23332.camel@gmail.com>
Date: Sat, 22 Nov 2025 01:05:09 -0800
From: Eduard Zingerman <eddyz87@...il.com>
To: Donglin Peng <dolinux.peng@...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, 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.