linux-kernel - Re: [RFC PATCH v1] btf: Sort BTF types by name and kind to optimize btf_find_by_name

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Message-ID: <CAADnVQLr0iSzV24Cyis0pconxyhZJKAuw-YQVoahxy-AvdNTvQ@mail.gmail.com>
Date: Tue, 14 Oct 2025 18:54:40 -0700
From: Alexei Starovoitov <alexei.starovoitov@...il.com>
To: Donglin Peng <dolinux.peng@...il.com>
Cc: Andrii Nakryiko <andrii.nakryiko@...il.com>, Andrii Nakryiko <andrii@...nel.org>, 
	LKML <linux-kernel@...r.kernel.org>, 
	linux-trace-kernel <linux-trace-kernel@...r.kernel.org>, bpf <bpf@...r.kernel.org>, 
	Eduard Zingerman <eddyz87@...il.com>, Alexei Starovoitov <ast@...nel.org>, Song Liu <song@...nel.org>, 
	Masami Hiramatsu <mhiramat@...nel.org>, Steven Rostedt <rostedt@...dmis.org>, 
	pengdonglin <pengdonglin@...omi.com>
Subject: Re: [RFC PATCH v1] btf: Sort BTF types by name and kind to optimize
 btf_find_by_name_kind lookup

On Mon, Oct 13, 2025 at 9:53 PM Donglin Peng <dolinux.peng@...il.com> wrote:
>
> I’d like to suggest a dual-mechanism approach:
> 1. If BTF is generated by a newer pahole (with pre-sorting support), the
>     kernel would use the pre-sorted data directly.
> 2. For BTF from older pahole versions, the kernel would handle sorting
>     at load time or later.

The problem with 2 is extra memory consumption for narrow
use case. The "time cat trace" example shows that search
is in critical path, but I suspect ftrace can do it differently.
I don't know why it's doing the search so much.
Everyelse in bpf we don't call it that often.
So optimizing the search is nice, but not at the expense
of so much extra memory.
Hence I don't think 2 is worth doing.

> Regarding the pahole changes: this is now my highest priority. I’ve
> already incorporated it into my development plan and will begin
> working on the patches shortly.

let's land pahole changes first.