From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S947159AbdDTTfc (ORCPT ); Thu, 20 Apr 2017 15:35:32 -0400 Received: from mail-io0-f196.google.com ([209.85.223.196]:32963 "EHLO mail-io0-f196.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S947078AbdDTTfY (ORCPT ); Thu, 20 Apr 2017 15:35:24 -0400 Subject: Re: [PATCH] of: introduce event tracepoints for dynamic device_node lifecyle To: Tyrel Datwyler , Michael Ellerman , Tyrel Datwyler , robh+dt@kernel.org References: <1492475525-10827-1-git-send-email-tyreld@linux.vnet.ibm.com> <58F6AA35.2040902@gmail.com> <87efwp6v4e.fsf@concordia.ellerman.id.au> <1d51a229-612b-bf09-93d5-6e43b476e2cf@gmail.com> <58F83C66.7030806@gmail.com> <64505d40-926d-b302-4ff3-dff71aa5018a@gmail.com> Cc: linuxppc-dev@lists.ozlabs.org, linux-kernel@vger.kernel.org, devicetree@vger.kernel.org, nfont@linux.vnet.ibm.com, rostedt@goodmis.org, mingo@redhat.com From: Frank Rowand Message-ID: <58F90D56.9070602@gmail.com> Date: Thu, 20 Apr 2017 12:34:46 -0700 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:38.0) Gecko/20100101 Thunderbird/38.4.0 MIME-Version: 1.0 In-Reply-To: <64505d40-926d-b302-4ff3-dff71aa5018a@gmail.com> Content-Type: text/plain; charset=windows-1252 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 04/20/17 09:51, Tyrel Datwyler wrote: > On 04/19/2017 09:43 PM, Frank Rowand wrote: > < snip > >> The call stack could easily be post-processed, for example using addr2line. >> Here is the call stack for when the refcount incremented to 23 from 22 (or >> more accurately, to 22 from 21): >> >> 0xc0d00e3c Line 857 of "init/main.c" >> 0xc03017d0 Line 792 of "init/main.c" >> 0xc0d3a234 Line 528 of "drivers/of/platform.c" >> 0xc0810684 Line 503 of "drivers/of/platform.c" >> 0xc081061c Line 267 of "include/linux/of.h" >> 0xc080d928 Line 815 of "drivers/of/base.c" >> >> Which ends up being this code: >> >> of_platform_default_populate_init() >> of_platform_default_populate() >> of_platform_populate() >> [[ of_find_node_by_path("/") ]] >> [[ of_find_node_opts_by_path(path, NULL) ]] >> of_node_get(of_root) >> >> Note that some functions can be left out of the ARM call stack, with >> a return going back more than one level. The functions in the call >> list above that are enclosed in '[[' and ']]' were found by source >> inspection in those cases. > > The same thing is encountered in ppc64 stack traces. I assume it is > generally inlining of small functions, but I've never actually verified > that theory. Probably should take the time to investigate, or just ask > someone. Yes, inlining small functions is one reason for this. Another case I often find is that when function A calls function B calls function C. If the final statement of function B is 'return C()' then there is no need for function C to return through function B, it can instead return directly to function A. (That is more a conceptual hand-waving of the idea, not the actual way the compiler implements it. Take this with a grain of salt, I'm not a compiler guy.) < snip >