Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756849AbXHQDoM (ORCPT ); Thu, 16 Aug 2007 23:44:12 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1752863AbXHQDnl (ORCPT ); Thu, 16 Aug 2007 23:43:41 -0400 Received: from ozlabs.org ([203.10.76.45]:52471 "EHLO ozlabs.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753672AbXHQDni (ORCPT ); Thu, 16 Aug 2007 23:43:38 -0400 MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Transfer-Encoding: 7bit Message-ID: <18117.6495.397597.582736@cargo.ozlabs.ibm.com> Date: Fri, 17 Aug 2007 13:43:27 +1000 From: Paul Mackerras To: Linus Torvalds Cc: Christoph Lameter , Chris Snook , Ilpo J?rvinen , Herbert Xu , Satyam Sharma , "Paul E. McKenney" , Stefan Richter , Linux Kernel Mailing List , linux-arch@vger.kernel.org, Netdev , Andrew Morton , ak@suse.de, heiko.carstens@de.ibm.com, David Miller , 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 In-Reply-To: References: <20070816003948.GY9645@linux.vnet.ibm.com> <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> <46C4ABA5.9010804@redhat.com> <18117.1287.779351.836552@cargo.ozlabs.ibm.com> X-Mailer: VM 7.19 under Emacs 21.4.1 Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1037 Lines: 21 Linus Torvalds writes: > In general, I'd *much* rather we used barriers. Anything that "depends" on > volatile is pretty much set up to be buggy. But I'm certainly also willing > to have that volatile inside "atomic_read/atomic_set()" if it avoids code > that would otherwise break - ie if it hides a bug. The cost of doing so seems to me to be well down in the noise - 44 bytes of extra kernel text on a ppc64 G5 config, and I don't believe the extra few cycles for the occasional extra load would be measurable (they should all hit in the L1 dcache). I don't mind if x86[-64] have atomic_read/set be nonvolatile and find all the missing barriers, but for now on powerpc, I think that not having to find those missing barriers is worth the 0.00076% increase in kernel text size. 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/