From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757453AbYCEPvW (ORCPT ); Wed, 5 Mar 2008 10:51:22 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1753335AbYCEPvM (ORCPT ); Wed, 5 Mar 2008 10:51:12 -0500 Received: from public.id2-vpn.continvity.gns.novell.com ([195.33.99.129]:31425 "EHLO public.id2-vpn.continvity.gns.novell.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753148AbYCEPvL convert rfc822-to-8bit (ORCPT ); Wed, 5 Mar 2008 10:51:11 -0500 Message-Id: <47CECF9E.76E4.0078.0@novell.com> X-Mailer: Novell GroupWise Internet Agent 7.0.3 Beta Date: Wed, 05 Mar 2008 15:51:42 +0000 From: "Jan Beulich" To: "Ingo Molnar" Cc: Subject: Re: profile_pc() bogus since <= 2.6.19 (x86 at least)? References: <47CE8EAD.76E4.0078.0@novell.com> <20080305153711.GC19300@elte.hu> In-Reply-To: <20080305153711.GC19300@elte.hu> Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 8BIT Content-Disposition: inline Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org >>> Ingo Molnar 05.03.08 16:37 >>> > >* Jan Beulich wrote: > >> Ingo, >> >> while the comment at the top of kernel/spinlock.c states so: >> >> * Note that some architectures have special knowledge about the >> * stack frames of these functions in their profile_pc. If you >> * change anything significant here that could change the stack >> * frame contact the architecture maintainers. >> >> the actual code doesn't seem to match this anymore. With all (and even >> before that, many) functions being written in C, there cannot be >> validly made assumptions about the stack frame layout. Indeed, if I >> check the disassembly framed by __lock_text_{start,end} on x86, there >> are a number of functions that push one or two registers (in >> lock_kernel() even stack variables are being allocated), which clearly >> breaks profile_pc()'s assumptions. >> >> Since it's been this way for so long, I wonder how frequently this >> code is actually being exercised... > >yeah - i guess it's not really relevant anymore now that lockdep saves >full stack traces. I doubt anyone bothers to look at wchan anymore. We >might even remove all the __lock and __sched sections and annotations? Since drivers/oprofile/cpu_buffer.c and kernel/profile.c both have a reference to profile_pc(), I'm not so sure about that. Perhaps if a replacement for these two can be found... Jan