From mboxrd@z Thu Jan 1 00:00:00 1970 From: Christoph Lameter Subject: Re: [PATCH 0/24] make atomic_read() behave consistently across all architectures Date: Wed, 15 Aug 2007 18:41:40 -0700 (PDT) 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 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 To: "Paul E. McKenney" 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 In-Reply-To: <20070816011414.GC9645@linux.vnet.ibm.com> Sender: netdev-owner@vger.kernel.org List-Id: netdev.vger.kernel.org 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()