Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S935398AbXHOWqb (ORCPT ); Wed, 15 Aug 2007 18:46:31 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S937247AbXHOWom (ORCPT ); Wed, 15 Aug 2007 18:44:42 -0400 Received: from e3.ny.us.ibm.com ([32.97.182.143]:39232 "EHLO e3.ny.us.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S936515AbXHOWoi (ORCPT ); Wed, 15 Aug 2007 18:44:38 -0400 Date: Wed, 15 Aug 2007 15:44:33 -0700 From: "Paul E. McKenney" To: Segher Boessenkool Cc: horms@verge.net.au, Stefan Richter , Satyam Sharma , Linux Kernel Mailing List , rpjday@mindspring.com, netdev@vger.kernel.org, ak@suse.de, cfriesen@nortel.com, Heiko Carstens , jesper.juhl@gmail.com, linux-arch@vger.kernel.org, Andrew Morton , zlynx@acm.org, clameter@sgi.com, schwidefsky@de.ibm.com, Chris Snook , Herbert Xu , davem@davemloft.net, Linus Torvalds , wensong@linux-vs.org, wjiang@resilience.com Subject: Re: [PATCH 0/24] make atomic_read() behave consistently across all architectures Message-ID: <20070815224433.GQ9645@linux.vnet.ibm.com> Reply-To: paulmck@linux.vnet.ibm.com References: <20070815081841.GA16551@osiris.boeblingen.de.ibm.com> <46C30540.2070603@s5r6.in-berlin.de> <20070815145207.GA23106@gondor.apana.org.au> <46C3253F.5090707@s5r6.in-berlin.de> <20070815162722.GD9645@linux.vnet.ibm.com> <20070815185724.GH9645@linux.vnet.ibm.com> <2c907d70a2267b887de346891758983d@kernel.crashing.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <2c907d70a2267b887de346891758983d@kernel.crashing.org> 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: 1999 Lines: 50 On Wed, Aug 15, 2007 at 11:05:35PM +0200, Segher Boessenkool wrote: > >>No; compilation units have nothing to do with it, GCC can optimise > >>across compilation unit boundaries just fine, if you tell it to > >>compile more than one compilation unit at once. > > > >Last I checked, the Linux kernel build system did compile each .c file > >as a separate compilation unit. > > I have some patches to use -combine -fwhole-program for Linux. > Highly experimental, you need a patched bleeding edge toolchain. > If there's interest I'll clean it up and put it online. > > David Woodhouse had some similar patches about a year ago. Sounds exciting... ;-) > >>>In many cases, the compiler also has to assume that > >>>msleep_interruptible() > >>>might call back into a function in the current compilation unit, thus > >>>possibly modifying global static variables. > >> > >>It most often is smart enough to see what compilation-unit-local > >>variables might be modified that way, though :-) > > > >Yep. For example, if it knows the current value of a given such local > >variable, and if all code paths that would change some other variable > >cannot be reached given that current value of the first variable. > > Or the most common thing: if neither the address of the translation- > unit local variable nor the address of any function writing to that > variable can "escape" from that translation unit, nothing outside > the translation unit can write to the variable. But there is usually at least one externally callable function in a .c file. > >At least given that gcc doesn't know about multiple threads of > >execution! > > Heh, only about the threads it creates itself (not relevant to > the kernel, for sure :-) ) ;-) Thanx, Paul - 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/