From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-1.0 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_PASS,URIBL_BLOCKED autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 5B36DC282DF for ; Fri, 19 Apr 2019 18:35:19 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 3457520449 for ; Fri, 19 Apr 2019 18:35:19 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728185AbfDSSfS convert rfc822-to-8bit (ORCPT ); Fri, 19 Apr 2019 14:35:18 -0400 Received: from mail.kernel.org ([198.145.29.99]:53888 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727526AbfDSS3Q (ORCPT ); Fri, 19 Apr 2019 14:29:16 -0400 Received: from gandalf.local.home (cpe-66-24-58-225.stny.res.rr.com [66.24.58.225]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id CD57421929; Fri, 19 Apr 2019 13:04:41 +0000 (UTC) Date: Fri, 19 Apr 2019 09:04:40 -0400 From: Steven Rostedt To: Ingo Molnar Cc: Peter Zijlstra , Linus Torvalds , Josh Poimboeuf , Thomas Gleixner , Peter Anvin , Julien Thierry , Will Deacon , Andy Lutomirski , Catalin Marinas , James Morse , valentin.schneider@arm.com, Brian Gerst , Andrew Lutomirski , Borislav Petkov , Denys Vlasenko , Linux List Kernel Mailing , Dmitry Vyukov , Slavomir Kaslev Subject: Re: [PATCH] compiler.h, tracing: Remove CONFIG_PROFILE_ALL_BRANCHES Message-ID: <20190419090440.640a46c2@gandalf.local.home> In-Reply-To: <20190419100837.GA19406@gmail.com> References: <20190307120317.GD32477@hirez.programming.kicks-ass.net> <20190307125526.GB32534@hirez.programming.kicks-ass.net> <20190307131312.GC32534@hirez.programming.kicks-ass.net> <20190307164705.qbu4ytdfdmsighas@treble> <20190307171709.dap5hfeof4yo3nsc@treble> <20190307173810.GI32477@hirez.programming.kicks-ass.net> <20190307131841.3b5d9e00@oasis.local.home> <20190310131620.GL2482@worktop.programming.kicks-ass.net> <20190419100837.GA19406@gmail.com> X-Mailer: Claws Mail 3.17.3 (GTK+ 2.24.32; x86_64-pc-linux-gnu) MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8BIT Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, 19 Apr 2019 12:08:37 +0200 Ingo Molnar wrote: > > Can't you just have those same engineers look at perf data? This seems > > like a very expensive and convoluted way of getting something. I haven't tried the perf data. How well does it work with running over a 2 weeks to a month period? That's what I do yearly. Here's the results of my last run: http://rostedt.homelinux.com/branches/gandalf-branches-2019/brach_all-2019-02-05 http://rostedt.homelinux.com/branches/mammoth-branches-2019/branch_all-2019-01-02 http://rostedt.homelinux.com/branches/mammoth-branches-2019/branch_all-2019-01-03 http://rostedt.homelinux.com/branches/mammoth-branches-2019/branch_all-2019-01-17 http://rostedt.homelinux.com/branches/mammoth-branches-2019/branch_all-2019-02-05 I have a cron job that runs nightly that copies the current state, and if the machine reboots, it starts a new file (which is why there's multiple files for mammoth - it rebooted). > > So since no-one offered objections to using perf branch profiling instead > (which method allows so much more than CONFIG_PROFILE_ALL_BRANCHES: such I've never used it, so I have no idea if it is suitable or not. > as profiling glibc and other user-space, or allowing to branch-profile > the kernel is an uninstrumented form not distorted by > CONFIG_PROFILE_ALL_BRANCHES code generation artifacts), lemme propose the > attached patch to remove if-tracing. > > If the CONFIG_PROFILE_ALL_BRANCHES=y feature is required for anyone it > can still be reverted privately or maintained out of tree - no need to > burden the mainline kernel with this. But is it a real burden? It's been in the kernel for over 10 years with very little issue. Only when we do something drastic does it show up, and it's usually a quick fix to get it working again. I believe Josh even told me that it found a bug in the objtool code, so it does still have benefit staying in the kernel even without people using it for profiling. Note, I'm in the middle of writing a LWN article about learning the kernel from branch profiling and it would be a shame if it disappears before I finish it. -- Steve > > I've build tested this and it Looks Perfect Here™.