Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756593AbXHPUCV (ORCPT ); Thu, 16 Aug 2007 16:02:21 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1751073AbXHPUCI (ORCPT ); Thu, 16 Aug 2007 16:02:08 -0400 Received: from mx1.redhat.com ([66.187.233.31]:40935 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750844AbXHPUCF (ORCPT ); Thu, 16 Aug 2007 16:02:05 -0400 Message-ID: <46C4AA26.4060707@redhat.com> Date: Thu, 16 Aug 2007 15:48:54 -0400 From: Chris Snook User-Agent: Thunderbird 1.5.0.12 (Macintosh/20070509) MIME-Version: 1.0 To: Herbert Xu CC: Stefan Richter , Paul Mackerras , Satyam Sharma , Christoph Lameter , "Paul E. McKenney" , Linux Kernel Mailing List , linux-arch@vger.kernel.org, Linus Torvalds , netdev@vger.kernel.org, Andrew Morton , ak@suse.de, heiko.carstens@de.ibm.com, davem@davemloft.net, schwidefsky@de.ibm.com, wensong@linux-vs.org, horms@verge.net.au, wjiang@resilience.com, cfriesen@nortel.com, zlynx@acm.org, rpjday@mindspring.com, jesper.juhl@gmail.com, segher@kernel.crashing.org Subject: Re: [PATCH 0/24] make atomic_read() behave consistently across all architectures References: <18115.44462.622801.683446@cargo.ozlabs.ibm.com> <20070816020042.GA30650@gondor.apana.org.au> <18115.45316.702491.681906@cargo.ozlabs.ibm.com> <18115.52863.638655.658466@cargo.ozlabs.ibm.com> <20070816053945.GB32442@gondor.apana.org.au> <18115.62741.807704.969977@cargo.ozlabs.ibm.com> <20070816070907.GA964@gondor.apana.org.au> <46C40587.7050708@s5r6.in-berlin.de> <20070816081049.GA1431@gondor.apana.org.au> In-Reply-To: <20070816081049.GA1431@gondor.apana.org.au> Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1247 Lines: 27 Herbert Xu wrote: > On Thu, Aug 16, 2007 at 10:06:31AM +0200, Stefan Richter wrote: >>> Do you (or anyone else for that matter) have an example of this? >> The only code I somewhat know, the ieee1394 subsystem, was perhaps >> authored and is currently maintained with the expectation that each >> occurrence of atomic_read actually results in a load operation, i.e. is >> not optimized away. This means all atomic_t (bus generation, packet and >> buffer refcounts, and some other state variables)* and likewise all >> atomic bitops in that subsystem. > > Can you find an actual atomic_read code snippet there that is > broken without the volatile modifier? A whole bunch of atomic_read uses will be broken without the volatile modifier once we start removing barriers that aren't needed if volatile behavior is guaranteed. barrier() clobbers all your registers. volatile atomic_read() only clobbers one register, and more often than not it's a register you wanted to clobber anyway. -- Chris - 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/