From patchwork Mon Jan 23 16:22:52 2023 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Steven Rostedt X-Patchwork-Id: 13112503 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 7129FC38142 for ; Mon, 23 Jan 2023 16:23:05 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231592AbjAWQXE (ORCPT ); Mon, 23 Jan 2023 11:23:04 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:55988 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230128AbjAWQXE (ORCPT ); Mon, 23 Jan 2023 11:23:04 -0500 Received: from sin.source.kernel.org (sin.source.kernel.org [145.40.73.55]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id C97C226BD; Mon, 23 Jan 2023 08:23:01 -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 sin.source.kernel.org (Postfix) with ESMTPS id 213EECE1398; Mon, 23 Jan 2023 16:22:58 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 9249AC433D2; Mon, 23 Jan 2023 16:22:55 +0000 (UTC) Date: Mon, 23 Jan 2023 11:22:52 -0500 From: Steven Rostedt To: LKML , Linux Trace Kernel Cc: Masami Hiramatsu , Mark Rutland Subject: [PATCH] ftrace/scripts: Update the instructions for ftrace-bisect.sh Message-ID: <20230123112252.022003dd@gandalf.local.home> X-Mailer: Claws Mail 3.17.8 (GTK+ 2.24.33; x86_64-pc-linux-gnu) MIME-Version: 1.0 Precedence: bulk List-ID: X-Mailing-List: linux-trace-kernel@vger.kernel.org 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 Fixes: f79b3f338564e ("ftrace: Allow enabling of filters via index of available_filter_functions") Signed-off-by: Steven Rostedt (Google) Acked-by: Mark Rutland --- scripts/tracing/ftrace-bisect.sh | 33 ++++++++++++++++++++++++-------- 1 file changed, 25 insertions(+), 8 deletions(-) diff --git a/scripts/tracing/ftrace-bisect.sh b/scripts/tracing/ftrace-bisect.sh index 926701162bc8..94ca73930f8a 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 +20,39 @@ # # # 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 will take several minutes. Setting multiple +# [old-way] functions is an O(n^2) operation, and we are dealing with thousands +# [old-way] of functions. So go have coffee, talk with your coworkers, read +# [old-way] facebook. And eventually, this operation 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 same. +# # # 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, this -# 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.