From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from netops-testserver-4-out.sgi.com ([192.48.171.29]:58651 "EHLO relay.sgi.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1760168AbXHPBlm (ORCPT ); Wed, 15 Aug 2007 21:41:42 -0400 Date: Wed, 15 Aug 2007 18:41:40 -0700 (PDT) From: Christoph Lameter Subject: Re: [PATCH 0/24] make atomic_read() behave consistently across all architectures In-Reply-To: <20070816011414.GC9645@linux.vnet.ibm.com> Message-ID: References: <46C2D6F3.3070707@s5r6.in-berlin.de> <18115.35524.56393.347841@cargo.ozlabs.ibm.com> <20070816003948.GY9645@linux.vnet.ibm.com> <20070816005348.GA9645@linux.vnet.ibm.com> <20070816011414.GC9645@linux.vnet.ibm.com> MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Sender: linux-arch-owner@vger.kernel.org To: "Paul E. McKenney" Cc: Paul Mackerras , Satyam Sharma , Stefan Richter , 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, Herbert Xu List-ID: On Wed, 15 Aug 2007, Paul E. McKenney wrote: > Understood. My point is not that the impact is precisely zero, but > rather that the impact on optimization is much less hurtful than the > problems that could arise otherwise, particularly as compilers become > more aggressive in their optimizations. The problems arise because barriers are not used as required. Volatile has wishy washy semantics and somehow marries memory barriers with data access. It is clearer to separate the two. Conceptual cleanness usually translates into better code. If one really wants the volatile then lets make it explicit and use atomic_read_volatile()