linux-kernel - Re: [RFC PATCH v2 2/5] btf: sort BTF types by kind and name to enable binary search

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Message-ID: <CAADnVQKU0MnQHxxvnp9WCu_UO4fEtd_D6ckNmOd7pLg90ecF4A@mail.gmail.com>
Date: Thu, 23 Oct 2025 08:52:56 -0700
From: Alexei Starovoitov <alexei.starovoitov@...il.com>
To: Donglin Peng <dolinux.peng@...il.com>
Cc: Eduard Zingerman <eddyz87@...il.com>, Alexei Starovoitov <ast@...nel.org>, 
	Andrii Nakryiko <andrii.nakryiko@...il.com>, Alan Maguire <alan.maguire@...cle.com>, 
	LKML <linux-kernel@...r.kernel.org>, bpf <bpf@...r.kernel.org>, 
	Song Liu <song@...nel.org>, pengdonglin <pengdonglin@...omi.com>
Subject: Re: [RFC PATCH v2 2/5] btf: sort BTF types by kind and name to enable
 binary search

On Thu, Oct 23, 2025 at 3:35 AM Donglin Peng <dolinux.peng@...il.com> wrote:
>
> On Thu, Oct 23, 2025 at 4:50 AM Eduard Zingerman <eddyz87@...il.com> wrote:
> >
> > On Wed, 2025-10-22 at 11:02 +0800, Donglin Peng wrote:
> > > On Wed, Oct 22, 2025 at 2:59 AM Eduard Zingerman <eddyz87@...il.com> wrote:
> > > >
> > > > On Mon, 2025-10-20 at 17:39 +0800, Donglin Peng wrote:
> > > > > This patch implements sorting of BTF types by their kind and name,
> > > > > enabling the use of binary search for type lookups.
> > > > >
> > > > > To share logic between kernel and libbpf, a new btf_sort.c file is
> > > > > introduced containing common sorting functionality.
> > > > >
> > > > > The sorting is performed during btf__dedup() when the new
> > > > > sort_by_kind_name option in btf_dedup_opts is enabled.
> > > >
> > > > Do we really need this option?  Dedup is free to rearrange btf types
> > > > anyway, so why not sort always?  Is execution time a concern?
> > >
> > > The issue is that sorting changes the layout of BTF. Many existing selftests
> > > rely on the current, non-sorted order for their validation checks. Introducing
> > > this as an optional feature first allows us to run it without immediately
> > > breaking the tests, giving us time to fix them incrementally.
> >
> > How many tests are we talking about?
> > The option is an API and it stays with us forever.
> > If the only justification for its existence is to avoid tests
> > modification, I don't think that's enough.
>
> I get your point, thanks. I wonder what others think?

+1 to Eduard's point.
No new flags please. Always sort.

Also I don't feel that sorting logic belongs in libbpf.
pahole needs to dedup first, apply extra filters, add extra BTFs.
At that point going back to libbpf and asking to sort seems odd.