Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754151AbYHMUWh (ORCPT ); Wed, 13 Aug 2008 16:22:37 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1751861AbYHMUW2 (ORCPT ); Wed, 13 Aug 2008 16:22:28 -0400 Received: from smtp1.linux-foundation.org ([140.211.169.13]:54137 "EHLO smtp1.linux-foundation.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751388AbYHMUW2 (ORCPT ); Wed, 13 Aug 2008 16:22:28 -0400 Date: Wed, 13 Aug 2008 13:21:22 -0700 (PDT) From: Linus Torvalds To: Andi Kleen cc: Steven Rostedt , Thomas Gleixner , Mathieu Desnoyers , Steven Rostedt , Jeremy Fitzhardinge , LKML , Ingo Molnar , Peter Zijlstra , Andrew Morton , David Miller , Roland McGrath , Ulrich Drepper , Rusty Russell , Gregory Haskins , Arnaldo Carvalho de Melo , "Luis Claudio R. Goncalves" , Clark Williams Subject: Re: Efficient x86 and x86_64 NOP microbenchmarks In-Reply-To: <20080813201532.GR1366@one.firstfloor.org> Message-ID: References: <20080813191926.GB15547@Krystal> <48A33D65.4020802@redhat.com> <20080813201532.GR1366@one.firstfloor.org> User-Agent: Alpine 1.10 (LFD 962 2008-03-14) MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 857 Lines: 22 On Wed, 13 Aug 2008, Andi Kleen wrote: > > Also I must say the whole ftrace noping exercise is pretty pointless without > avoiding frame pointers because it does save less than what you lose > unconditionally from the "select FRAME_POINTER" Andi, you seem to have missed the whole point. This is a _correctness_ issue as long as the nop is not a single instruction. And the workaround for that is uglier than just making a single-instruction nop. So the question now is to find a good nop that _is_ a single atomic instruction. Your blathering about frame pointers is missing the whole point! Linus -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/