From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752092Ab2DNIz1 (ORCPT ); Sat, 14 Apr 2012 04:55:27 -0400 Received: from mail-we0-f174.google.com ([74.125.82.174]:35730 "EHLO mail-we0-f174.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750956Ab2DNIzZ (ORCPT ); Sat, 14 Apr 2012 04:55:25 -0400 Date: Sat, 14 Apr 2012 10:55:19 +0200 From: Ingo Molnar To: Arnaldo Carvalho de Melo Cc: Linus Torvalds , hpa@zytor.com, paulus@samba.org, eranian@google.com, linux-kernel@vger.kernel.org, efault@gmx.de, peterz@infradead.org, namhyung@gmail.com, fweisbec@gmail.com, dsahern@gmail.com, Masami Hiramatsu , tglx@linutronix.de, linux-tip-commits@vger.kernel.org Subject: Re: [tip:perf/core] perf ui annotate browser: Allow toggling addr offset view Message-ID: <20120414085519.GB28505@gmail.com> References: <20120414010410.GB22114@infradead.org> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <20120414010410.GB22114@infradead.org> User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org * Arnaldo Carvalho de Melo wrote: > Em Fri, Apr 13, 2012 at 11:30:52AM -0700, Linus Torvalds escreveu: > > On Fri, Apr 13, 2012 at 11:25 AM, Linus Torvalds > > wrote: > > > > > > : > > >    1.91 :          push   %rbp > > > > Oh, btw, talking about kmem_cache_free: that one uses altinstructions, > > and so perf report shows the hottest instruction wrong (and I'm not > > talking about "ugly"): > > Well, if we use Masami's disassembler we would use the actual > code as it is being used and not the original DSO that was > later patched by altinstructions. Key would be to use the kernel's live RAM image of instructions. I.e. we should provide a live /proc/vmlinux image in essence: a 'virtual' ELF binary image constructed out of the live kernel RAM image - with no extra RAM overhead. (Maybe with modules included in an intelligent way - although personally I don't use modules when I instrument the kernel) That plus the always-available /proc/kallsyms would offer rather powerful annotation already: without *any* debug info - out of box, on any Linux installation. (This was always the main advantage of /proc/profile and readprofile btw: it worked everywhere while most other profiling solutions needed a debuginfo, etc.) Doing /proc/vmlinux would be different from /dev/mem as it only shows the kernel RAM image, and only in a read-only fashion. Default permissions of /proc/vmlinux should probably track console permissions: it should be possible to allow people sitting in front of the computer to read /proc/vmlinux, while people logged in over the network wouldn't. Doing such a live kernel vmlinux would have other debugging and instrumentation advantages as well: various code patching effects could be checked and observed directly. Thanks, Ingo