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

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Message-ID: <20250102153016.7fc5e443@gandalf.local.home>
Date: Thu, 2 Jan 2025 15:30:16 -0500
From: Steven Rostedt <rostedt@...dmis.org>
To: Peter Zijlstra <peterz@...radead.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, 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.

-- Steve