From mboxrd@z Thu Jan 1 00:00:00 1970 From: "Paul E. McKenney" Subject: Re: [PATCH 2/2]: atomic_t: Remove volatile from atomic_t definition Date: Wed, 19 May 2010 15:50:46 -0700 Message-ID: <20100519225046.GO2237@linux.vnet.ibm.com> References: <20100519130327.GW2516@laptop> <20100519150132.GJ2237@linux.vnet.ibm.com> <20100519.125449.56392211.davem@davemloft.net> Reply-To: paulmck@linux.vnet.ibm.com Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: Received: from e7.ny.us.ibm.com ([32.97.182.137]:55814 "EHLO e7.ny.us.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751475Ab0ESWuu (ORCPT ); Wed, 19 May 2010 18:50:50 -0400 Content-Disposition: inline In-Reply-To: <20100519.125449.56392211.davem@davemloft.net> Sender: linux-arch-owner@vger.kernel.org List-ID: To: David Miller Cc: npiggin@suse.de, torvalds@linux-foundation.org, anton@samba.org, akpm@linux-foundation.org, willy@linux.intel.com, benh@kernel.crashing.org, paulus@samba.org, linux-arch@vger.kernel.org, linux-kernel@vger.kernel.org On Wed, May 19, 2010 at 12:54:49PM -0700, David Miller wrote: > From: "Paul E. McKenney" > Date: Wed, 19 May 2010 08:01:32 -0700 > > > On Wed, May 19, 2010 at 11:03:27PM +1000, Nick Piggin wrote: > >> For atomic_read it shouldn't matter unless gcc is *really* bad at it. > >> Ah, for atomic_read, the required semantic is surely ACCESS_ONCE, so > >> that's where the volatile is needed? (maybe it would be clearer to > >> explicitly use ACCESS_ONCE?) > > > > Explicit use of ACCESS_ONCE() where needed makes a lot of sense to me, > > and allows better code to be generated for initialization and cleanup > > code where no other task has access to the atomic_t. > > I agree and I want to see this too, but I think with the tree the size > that it is we have to work backwards at this point. > > Existing behavior by default, and optimized cases get tagged by using > a new interface (atomic_read_light(), test_bit{,s}_light(), etc.) Fair enough! Thanx, Paul