From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752220Ab0CSDGL (ORCPT ); Thu, 18 Mar 2010 23:06:11 -0400 Received: from mail-bw0-f209.google.com ([209.85.218.209]:39636 "EHLO mail-bw0-f209.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751458Ab0CSDGJ (ORCPT ); Thu, 18 Mar 2010 23:06:09 -0400 DomainKey-Signature: a=rsa-sha1; c=nofws; d=gmail.com; s=gamma; h=date:from:to:cc:subject:message-id:references:mime-version :content-type:content-disposition:in-reply-to:user-agent; b=fBQKnbovtngua5fVVUMvDlWAZ9MorkQXr00T4AnlvG1A4uuryuxEjvz94TwnFWOU3L R7/jYnyslxxAGQTYDSHDBiWkFUscPc82qbH4g4O0wlNA0/tPpn0D5vBxAVmvhs9LBAQ/ iP0J6qG/eHFxbLjGJcBKU98VAMr6ikghjMBeo= Date: Fri, 19 Mar 2010 04:06:13 +0100 From: Frederic Weisbecker To: Mathieu Desnoyers Cc: Hitoshi Mitake , Jason Baron , Steven Rostedt , Ingo Molnar , Peter Zijlstra , linux-kernel@vger.kernel.org, h.mitake@gmail.com, Paul Mackerras , Arnaldo Carvalho de Melo , Jens Axboe Subject: Re: [PATCH RFC 00/11] lock monitor: Separate features related to lock Message-ID: <20100319030611.GE22095@nowhere> References: <1268590435.9440.8.camel@laptop> <20100317013236.GB5258@nowhere> <20100317095230.GD17146@elte.hu> <4BA1C141.8050409@dcl.info.waseda.ac.jp> <20100318211633.GG5103@nowhere> <20100319010857.GC23020@Krystal> <20100319012337.GA22095@nowhere> <20100319013658.GB28456@Krystal> <20100319022659.GC22095@nowhere> <20100319024042.GB28941@Krystal> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20100319024042.GB28941@Krystal> User-Agent: Mutt/1.5.18 (2008-05-17) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Mar 18, 2010 at 10:40:42PM -0400, Mathieu Desnoyers wrote: > Well, the use-case that drove the asm goto implementation _is_ the tracepoints. > ;) > > > > > But, looking at __DO_TRACE: > > > > if (it_func) { \ > > do { \ > > ((void(*)(proto))(*it_func))(args); \ > > } while (*(++it_func)); \ > > } > > > > I would expect the compiler not to load the parameters in the stack > > before first checking the branch. > > Note that you have to put that in its full context. It's a macro expanded within > a static inline function. The initial parameters are passed to the static > inline, not directly as "args" here. So parameters with side-effects have to be > evaluated before their result can be passed to the static inline function, so in > that sense their evaluation cannot be moved into the conditional branch. Evaluation yeah, I agree. A function passed as an argument is going to be evaluated indeed, or whatever thing that has a side effect. But there is nothing here that need to setup the parameters to the stack right before the true tracepoint call, not until we passed the branch check once. > > So, the fact that parameters are not loaded before we know we'll call > > the tracepoint is something we already have or is it something that the jump > > label brings in the package somehow? > > It's standard compiler optimization behavior. Sure. My doubt is: currently with the upstream version, does the compiler tend to load the parameters to the stack before the branch is checked? Or is this a magic that jmp labels bring for whatever reason? Thanks.