From nobody Sun Sep 14 09:38:21 2025 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 8E9F9C25B4E for ; Tue, 24 Jan 2023 18:16:14 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S233911AbjAXSQM (ORCPT ); Tue, 24 Jan 2023 13:16:12 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:59890 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S232517AbjAXSQL (ORCPT ); Tue, 24 Jan 2023 13:16:11 -0500 Received: from dfw.source.kernel.org (dfw.source.kernel.org [139.178.84.217]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 7BDAD4A210; Tue, 24 Jan 2023 10:16:04 -0800 (PST) Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by dfw.source.kernel.org (Postfix) with ESMTPS id 1799E61312; Tue, 24 Jan 2023 18:16:04 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id E8F37C433D2; Tue, 24 Jan 2023 18:16:02 +0000 (UTC) Date: Tue, 24 Jan 2023 13:16:01 -0500 From: Steven Rostedt To: LKML , Linux Trace Kernel Cc: Masami Hiramatsu , Mark Rutland Subject: [PATCH v2] ftrace/scripts: Update the instructions for ftrace-bisect.sh Message-ID: <20230124131601.1506b286@gandalf.local.home> X-Mailer: Claws Mail 3.17.8 (GTK+ 2.24.33; x86_64-pc-linux-gnu) MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Type: text/plain; charset="utf-8" From: "Steven Rostedt (Google)" The instructions for the ftrace-bisect.sh script, which is used to find what function is being traced that is causing a kernel crash, and possibly a triple fault reboot, uses the old method. In 5.1, a new feature was added that let the user write in the index into available_filter_functions that maps to the function a user wants to set in set_ftrace_filter (or set_ftrace_notrace). This takes O(1) to set, as suppose to writing a function name, which takes O(n) (where n is the number of functions in available_filter_functions). The ftrace-bisect.sh requires setting half of the functions in available_filter_functions, which is O(n^2) using the name method to enable and can take several minutes to complete. The number method is O(n) which takes less than a second to complete. Using the number method for any kernel 5.1 and after is the proper way to do the bisect. Update the usage to reflect the new change, as well as using the /sys/kernel/tracing path instead of the obsolete debugfs path. Cc: stable@vger.kernel.org Cc: Masami Hiramatsu Acked-by: Mark Rutland Fixes: f79b3f338564e ("ftrace: Allow enabling of filters via index of avail= able_filter_functions") Signed-off-by: Steven Rostedt (Google) --- Changes since v1: https://lkml.kernel.org/r/20230123112252.022003dd@gandalf= .local.home - Slight rewrote the "Note" section. (Mark Rutland) scripts/tracing/ftrace-bisect.sh | 34 ++++++++++++++++++++++++-------- 1 file changed, 26 insertions(+), 8 deletions(-) diff --git a/scripts/tracing/ftrace-bisect.sh b/scripts/tracing/ftrace-bise= ct.sh index 926701162bc8..bb4f59262bbe 100755 --- a/scripts/tracing/ftrace-bisect.sh +++ b/scripts/tracing/ftrace-bisect.sh @@ -12,7 +12,7 @@ # (note, if this is a problem with function_graph tracing, then simply # replace "function" with "function_graph" in the following steps). # -# # cd /sys/kernel/debug/tracing +# # cd /sys/kernel/tracing # # echo schedule > set_ftrace_filter # # echo function > current_tracer # @@ -20,22 +20,40 @@ # # # echo nop > current_tracer # -# # cat available_filter_functions > ~/full-file +# Starting with v5.1 this can be done with numbers, making it much faster: +# +# The old (slow) way, for kernels before v5.1. +# +# [old-way] # cat available_filter_functions > ~/full-file +# +# [old-way] *** Note *** this process will take several minutes to update= the +# [old-way] filters. Setting multiple functions is an O(n^2) operation, an= d we +# [old-way] are dealing with thousands of functions. So go have coffee, ta= lk +# [old-way] with your coworkers, read facebook. And eventually, this opera= tion +# [old-way] will end. +# +# The new way (using numbers) is an O(n) operation, and usually takes less= than a second. +# +# seq `wc -l available_filter_functions | cut -d' ' -f1` > ~/full-file +# +# This will create a sequence of numbers that match the functions in +# available_filter_functions, and when echoing in a number into the +# set_ftrace_filter file, it will enable the corresponding function in +# O(1) time. Making enabling all functions O(n) where n is the number of +# functions to enable. +# +# For either the new or old way, the rest of the operations remain the sam= e. +# # # ftrace-bisect ~/full-file ~/test-file ~/non-test-file # # cat ~/test-file > set_ftrace_filter # -# *** Note *** this will take several minutes. Setting multiple functions = is -# an O(n^2) operation, and we are dealing with thousands of functions. So = go -# have coffee, talk with your coworkers, read facebook. And eventually, t= his -# operation will end. -# # # echo function > current_tracer # # If it crashes, we know that ~/test-file has a bad function. # # Reboot back to test kernel. # -# # cd /sys/kernel/debug/tracing +# # cd /sys/kernel/tracing # # mv ~/test-file ~/full-file # # If it didn't crash. --=20 2.39.0