linux-kernel - Re: [PATCH 14/14] scripts/sorttable: ftrace: Do not add weak functions to available_filter

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Message-ID: <20250102203625.GF7274@noisy.programming.kicks-ass.net>
Date: Thu, 2 Jan 2025 21:36:25 +0100
From: Peter Zijlstra <peterz@...radead.org>
To: Steven Rostedt <rostedt@...dmis.org>
Cc: linux-kernel@...r.kernel.org, linux-trace-kernel@...r.kernel.org,
	linux-kbuild@...r.kernel.org, bpf <bpf@...r.kernel.org>,
	Masami Hiramatsu <mhiramat@...nel.org>,
	Mark Rutland <mark.rutland@....com>,
	Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Masahiro Yamada <masahiroy@...nel.org>,
	Nathan Chancellor <nathan@...nel.org>,
	Nicolas Schier <nicolas@...sle.eu>,
	Zheng Yejian <zhengyejian1@...wei.com>,
	Martin Kelly <martin.kelly@...wdstrike.com>,
	Christophe Leroy <christophe.leroy@...roup.eu>,
	Josh Poimboeuf <jpoimboe@...hat.com>
Subject: Re: [PATCH 14/14] scripts/sorttable: ftrace: Do not add weak
 functions to available_filter_functions

On Thu, Jan 02, 2025 at 03:30:16PM -0500, Steven Rostedt wrote:
> On Thu, 2 Jan 2025 21:24:04 +0100
> Peter Zijlstra <peterz@...radead.org> wrote:
> 
> > It is not. If kallsyms is fixed, you can use that to tell which
> > fentry/mcount sites are 'invalid'.
> 
> I can't use kallsyms for valid tests at boot up. Even with a binary search,
> it's still rather slow. The ftrace table is created at early boot, even
> before scheduling (it's needed before you can enable boot time function
> tracing), so any slow down in creating that table slows down the boot, and
> people will notice.

I'm not sure I understand, up until you've started userspace, nobody
cares about those weird indexes.