Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1762996AbXHPHKs (ORCPT ); Thu, 16 Aug 2007 03:10:48 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1754988AbXHPHKd (ORCPT ); Thu, 16 Aug 2007 03:10:33 -0400 Received: from rhun.apana.org.au ([64.62.148.172]:4725 "EHLO arnor.apana.org.au" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1754769AbXHPHKb (ORCPT ); Thu, 16 Aug 2007 03:10:31 -0400 Date: Thu, 16 Aug 2007 15:09:07 +0800 From: Herbert Xu To: Paul Mackerras Cc: Satyam Sharma , Christoph Lameter , "Paul E. McKenney" , 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 Subject: Re: [PATCH 0/24] make atomic_read() behave consistently across all architectures Message-ID: <20070816070907.GA964@gondor.apana.org.au> 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> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <18115.62741.807704.969977@cargo.ozlabs.ibm.com> User-Agent: Mutt/1.5.9i Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1488 Lines: 36 On Thu, Aug 16, 2007 at 04:56:21PM +1000, Paul Mackerras wrote: > > Note that I said these are the cases _where one might want to allow > caching_, so of course adding volatile doesn't help _these_ cases. > There are of course other cases where one definitely doesn't want to > allow the compiler to cache the value, such as when polling an atomic > variable waiting for another CPU to change it, and from my inspection > so far these cases seem to be the majority. We've been through that already. If it's a busy-wait it should use cpu_relax. If it's scheduling away that already forces the compiler to reread anyway. Do you have an actual example where volatile is needed? > - It matches the normal expectation based on the name "atomic_read" > - It matches the behaviour of the other atomic_* primitives Can't argue since you left out what those expectations or properties are. > - It avoids bugs in the cases where "volatile" behaviour is required Do you (or anyone else for that matter) have an example of this? Cheers, -- Visit Openswan at http://www.openswan.org/ Email: Herbert Xu ~{PmV>HI~} Home Page: http://gondor.apana.org.au/~herbert/ PGP Key: http://gondor.apana.org.au/~herbert/pubkey.txt - 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/