From: Steven Rostedt <rostedt@goodmis.org>
To: Lawrence Lin via B4 Relay <devnull+deduce.gmail.com@kernel.org>
Cc: deduce@gmail.com, Masami Hiramatsu <mhiramat@kernel.org>,
Mark Rutland <mark.rutland@arm.com>,
Mathieu Desnoyers <mathieu.desnoyers@efficios.com>,
Petr Pavlu <petr.pavlu@suse.com>,
linux-modules@vger.kernel.org, Stanislaw Gruszka <stf_xl@wp.pl>,
linux-kernel@vger.kernel.org, linux-trace-kernel@vger.kernel.org
Subject: Re: [PATCH] ftrace: Avoid quadratic symbol lookups in ftrace_module_enable()
Date: Sun, 4 Oct 2026 05:09:04 -0400 [thread overview]
Message-ID: <20261004050904.06a5ecab@fedora> (raw)
In-Reply-To: <20261003-ftrace-mod-bsearch-v1-1-92e2fd2d80ff@gmail.com>
On Sat, 03 Oct 2026 11:27:10 -0500
Lawrence Lin via B4 Relay <devnull+deduce.gmail.com@kernel.org> wrote:
> From: Lawrence Lin <deduce@gmail.com>
>
> Since commit b39181f7c690 ("ftrace: Add FTRACE_MCOUNT_MAX_OFFSET to avoid
> adding weak function"), ftrace_module_enable() calls test_for_valid_rec()
> for every ftrace record of a module being loaded. test_for_valid_rec()
> resolves the record address with kallsyms_lookup(), and for a module
> address find_kallsyms_symbol() scans the whole symbol table of the module.
> Loading a module therefore costs O(records * symbols), all of it under
> ftrace_lock.
Honestly, I think we can revert commit b39181f7c690.
Since commit ef378c3b823385 ("scripts/sorttable: Zero out weak
functions in mcount_loc table"), I believe that commit has become
obsolete. I just kept it because I didn't want to add regressions.
It would be interesting if it actually triggers (finds something). If
it doesn't, then I think we should just remove that code instead of
adding more complexity to it.
-- Steve
next prev parent reply other threads:[~2026-10-04 9:09 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-10-03 16:27 [PATCH] ftrace: Avoid quadratic symbol lookups in ftrace_module_enable() Lawrence Lin via B4 Relay
2026-10-03 16:27 ` Lawrence Lin
2026-10-04 3:03 ` Lawrence Lin
2026-10-04 9:00 ` David Laight
2026-10-04 17:05 ` Lawrence Lin
2026-10-04 9:09 ` Steven Rostedt [this message]
2026-10-04 17:05 ` Lawrence Lin
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