Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S934337AbXHMFRX (ORCPT ); Mon, 13 Aug 2007 01:17:23 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1752832AbXHMFRJ (ORCPT ); Mon, 13 Aug 2007 01:17:09 -0400 Received: from rhun.apana.org.au ([64.62.148.172]:1387 "EHLO arnor.apana.org.au" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1752666AbXHMFRH (ORCPT ); Mon, 13 Aug 2007 01:17:07 -0400 From: Herbert Xu To: paulmck@linux.vnet.ibm.com Subject: Re: [PATCH 6/24] make atomic_read() behave consistently on frv Cc: herbert@gondor.apana.org.au, csnook@redhat.com, dhowells@redhat.com, linux-kernel@vger.kernel.org, linux-arch@vger.kernel.org, torvalds@linux-foundation.org, netdev@vger.kernel.org, akpm@linux-foundation.org, 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 Organization: Core In-Reply-To: <20070811042943.GA13410@linux.vnet.ibm.com> X-Newsgroups: apana.lists.os.linux.kernel,apana.lists.os.linux.netdev User-Agent: tin/1.7.4-20040225 ("Benbecula") (UNIX) (Linux/2.6.17-rc4 (i686)) Message-Id: Date: Mon, 13 Aug 2007 13:15:52 +0800 Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1416 Lines: 32 Paul E. McKenney wrote: > On Sat, Aug 11, 2007 at 08:54:46AM +0800, Herbert Xu wrote: >> Chris Snook wrote: >> > >> > cpu_relax() contains a barrier, so it should do the right thing. For >> > non-smp architectures, I'm concerned about interacting with interrupt >> > handlers. Some drivers do use atomic_* operations. >> >> What problems with interrupt handlers? Access to int/long must >> be atomic or we're in big trouble anyway. > > Reordering due to compiler optimizations. CPU reordering does not > affect interactions with interrupt handlers on a given CPU, but > reordering due to compiler code-movement optimization does. Since > volatile can in some cases suppress code-movement optimizations, > it can affect interactions with interrupt handlers. If such reordering matters, then you should use one of the *mb macros or barrier() rather than relying on possibly hidden volatile cast. 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/