Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751670AbWIZAuu (ORCPT ); Mon, 25 Sep 2006 20:50:50 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1751674AbWIZAuu (ORCPT ); Mon, 25 Sep 2006 20:50:50 -0400 Received: from tomts36.bellnexxia.net ([209.226.175.93]:54488 "EHLO tomts36-srv.bellnexxia.net") by vger.kernel.org with ESMTP id S1751668AbWIZAut (ORCPT ); Mon, 25 Sep 2006 20:50:49 -0400 Date: Mon, 25 Sep 2006 20:45:35 -0400 From: Mathieu Desnoyers To: Jeremy Fitzhardinge Cc: Martin Bligh , "Frank Ch. Eigler" , Masami Hiramatsu , prasanna@in.ibm.com, Andrew Morton , Ingo Molnar , Paul Mundt , linux-kernel , Jes Sorensen , Tom Zanussi , Richard J Moore , Michel Dagenais , Christoph Hellwig , Greg Kroah-Hartman , Thomas Gleixner , William Cohen , ltt-dev@shafik.org, systemtap@sources.redhat.com, Alan Cox , Karim Yaghmour , Pavel Machek , Joe Perches , "Randy.Dunlap" , "Jose R. Santos" Subject: Re: [PATCH] Linux Kernel Markers 0.13 for 2.6.17 Message-ID: <20060926004535.GA2978@Krystal> References: <20060925233349.GA2352@Krystal> <20060925235617.GA3147@Krystal> <45187146.8040302@goop.org> <20060926002551.GA18276@Krystal> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Transfer-Encoding: 7bit Content-Disposition: inline In-Reply-To: <20060926002551.GA18276@Krystal> X-Editor: vi X-Info: http://krystal.dyndns.org:8080 X-Operating-System: Linux/2.4.32-grsec (i686) X-Uptime: 20:37:18 up 33 days, 21:45, 3 users, load average: 0.08, 0.14, 0.18 User-Agent: Mutt/1.5.13 (2006-08-11) Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1872 Lines: 54 * Mathieu Desnoyers (mathieu.desnoyers@polymtl.ca) wrote: > Yes, preempt_disable() has a barrier(), on gcc : > __asm__ __volatile__("": : :"memory"). > > > > Either way, this doesn't prevent some otherwise unrelated > > non-memory-using code from being scheduled in there, which would not be > > executed. The gcc manual really strongly discourages jumping between > > inline asms, because they have basically unpredictable results. > > > > Ok, I will do the call in assembly then. > Before I rush on a solution too fast... I have a question for you : To protect code from being preempted, the macros preempt_disable and preempt_enable must normally be used. Logically, this macro must make sure gcc doesn't interleave preemptible code and non-preemptible code. Starting with this hypothesis, what makes gcc aware of this ? If we check preempt_disable (the disable call is almost symmetric) : linux/preempt.h: define add_preempt_count(val) do { preempt_count() += (val); } while (0) #define inc_preempt_count() add_preempt_count(1) #define preempt_disable() \ do { \ inc_preempt_count(); \ barrier(); \ } while (0) So the magic must be in the barrier() macro : linux/compiler-gcc.h: /* Optimization barrier */ /* The "volatile" is due to gcc bugs */ #define barrier() __asm__ __volatile__("": : :"memory") Which makes me think that if I put barriers around my asm, call, asm trio, no other code will be interleaved. Is it right ? Mathieu OpenPGP public key: http://krystal.dyndns.org:8080/key/compudj.gpg Key fingerprint: 8CD5 52C3 8E3C 4140 715F BA06 3F25 A8FE 3BAE 9A68 - 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/