Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1763460AbXHQABU (ORCPT ); Thu, 16 Aug 2007 20:01:20 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1757149AbXHQABJ (ORCPT ); Thu, 16 Aug 2007 20:01:09 -0400 Received: from rhun.apana.org.au ([64.62.148.172]:3222 "EHLO arnor.apana.org.au" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1756671AbXHQABH (ORCPT ); Thu, 16 Aug 2007 20:01:07 -0400 Date: Fri, 17 Aug 2007 07:59:02 +0800 From: Herbert Xu To: "Paul E. McKenney" Cc: Stefan Richter , Paul Mackerras , Satyam Sharma , Christoph Lameter , Chris Snook , 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 Message-ID: <20070816235902.GB11594@gondor.apana.org.au> References: <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> <46C41EE4.9090806@s5r6.in-berlin.de> <46C42767.4070104@s5r6.in-berlin.de> <20070816104250.GB2927@gondor.apana.org.au> <20070816163441.GB16957@linux.vnet.ibm.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20070816163441.GB16957@linux.vnet.ibm.com> User-Agent: Mutt/1.5.9i Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1453 Lines: 36 On Thu, Aug 16, 2007 at 09:34:41AM -0700, Paul E. McKenney wrote: > > The compiler can also reorder non-volatile accesses. For an example > patch that cares about this, please see: > > http://lkml.org/lkml/2007/8/7/280 > > This patch uses an ORDERED_WRT_IRQ() in rcu_read_lock() and > rcu_read_unlock() to ensure that accesses aren't reordered with respect > to interrupt handlers and NMIs/SMIs running on that same CPU. Good, finally we have some code to discuss (even though it's not actually in the kernel yet). First of all, I think this illustrates that what you want here has nothing to do with atomic ops. The ORDERED_WRT_IRQ macro occurs a lot more times in your patch than atomic reads/sets. So *assuming* that it was necessary at all, then having an ordered variant of the atomic_read/atomic_set ops could do just as well. However, I still don't know which atomic_read/atomic_set in your patch would be broken if there were no volatile. Could you please point them out? Cheers, -- Visit Openswan at http://www.openswan.org/ Email: Herbert Xu ~{PmV>HI~} Home Page: http://gondor.apana.org.au/~herbert/ PGP Key: http://gondor.apana.org.au/~herbert/pubkey.txt - 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/