From mboxrd@z Thu Jan 1 00:00:00 1970 From: "Paul E. McKenney" Subject: Re: [PATCH 0/24] make atomic_read() behave consistently across all architectures Date: Wed, 15 Aug 2007 17:53:48 -0700 Message-ID: <20070816005348.GA9645@linux.vnet.ibm.com> References: <20070809131423.GA9927@shell.boston.redhat.com> <46C2D6F3.3070707@s5r6.in-berlin.de> <18115.35524.56393.347841@cargo.ozlabs.ibm.com> <20070816003948.GY9645@linux.vnet.ibm.com> Reply-To: paulmck@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: Christoph Lameter Return-path: Received: from e2.ny.us.ibm.com ([32.97.182.142]:38143 "EHLO e2.ny.us.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S937499AbXHPAxx (ORCPT ); Wed, 15 Aug 2007 20:53:53 -0400 Content-Disposition: inline In-Reply-To: Sender: netdev-owner@vger.kernel.org List-Id: netdev.vger.kernel.org On Wed, Aug 15, 2007 at 05:42:07PM -0700, Christoph Lameter wrote: > On Wed, 15 Aug 2007, Paul E. McKenney wrote: > > > Seems to me that we face greater chance of confusion without the > > volatile than with, particularly as compiler optimizations become > > more aggressive. Yes, we could simply disable optimization, but > > optimization can be quite helpful. > > A volatile default would disable optimizations for atomic_read. > atomic_read without volatile would allow for full optimization by the > compiler. Seems that this is what one wants in many cases. The volatile cast should not disable all that many optimizations, for example, it is much less hurtful than barrier(). Furthermore, the main optimizations disabled (pulling atomic_read() and atomic_set() out of loops) really do need to be disabled. Thanx, Paul