Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S937524AbXHPB0r (ORCPT ); Wed, 15 Aug 2007 21:26:47 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1762951AbXHPB0a (ORCPT ); Wed, 15 Aug 2007 21:26:30 -0400 Received: from gate.crashing.org ([63.228.1.57]:34184 "EHLO gate.crashing.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1760662AbXHPB02 (ORCPT ); Wed, 15 Aug 2007 21:26:28 -0400 In-Reply-To: <20070815224433.GQ9645@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> <20070815224433.GQ9645@linux.vnet.ibm.com> Mime-Version: 1.0 (Apple Message framework v623) Content-Type: text/plain; charset=US-ASCII; format=flowed Message-Id: Content-Transfer-Encoding: 7bit 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 From: Segher Boessenkool Subject: Re: [PATCH 0/24] make atomic_read() behave consistently across all architectures Date: Thu, 16 Aug 2007 03:23:28 +0200 To: paulmck@linux.vnet.ibm.com X-Mailer: Apple Mail (2.623) Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1918 Lines: 51 >>>> 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... ;-) Yeah, the breakage is *quite* spectacular :-) >>>>> 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. Of course, but often none of those will (indirectly) write a certain static variable. Segher - 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/