Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1760594AbXHPKhv (ORCPT ); Thu, 16 Aug 2007 06:37:51 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1757715AbXHPKhi (ORCPT ); Thu, 16 Aug 2007 06:37:38 -0400 Received: from rhun.apana.org.au ([64.62.148.172]:2686 "EHLO arnor.apana.org.au" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1752009AbXHPKhg (ORCPT ); Thu, 16 Aug 2007 06:37:36 -0400 Date: Thu, 16 Aug 2007 18:35:47 +0800 From: Herbert Xu To: Stefan Richter Cc: Paul Mackerras , Satyam Sharma , Christoph Lameter , "Paul E. McKenney" , 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: <20070816103547.GA2927@gondor.apana.org.au> References: <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> <20070816070907.GA964@gondor.apana.org.au> <46C40587.7050708@s5r6.in-berlin.de> <20070816081049.GA1431@gondor.apana.org.au> <46C41EE4.9090806@s5r6.in-berlin.de> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <46C41EE4.9090806@s5r6.in-berlin.de> User-Agent: Mutt/1.5.9i Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1311 Lines: 27 On Thu, Aug 16, 2007 at 11:54:44AM +0200, Stefan Richter wrote: > > One example was discussed here earlier: The for (;;) loop in > nodemgr_host_thread. There an msleep_interruptible implicitly acted as > barrier (at the moment because it's in a different translation unit; if > it were the same, then because it hopefully has own barriers). So that > happens to work, although such an implicit barrier is bad style: Better > enforce the desired behaviour (== guaranteed load operation) *explicitly*. Hmm, it's not bad style at all. Let's assume that everything is in the same scope. Such a loop must either call a function that busy-waits, which should always have a cpu_relax or something equivalent, or it'll call a function that schedules away which immediately invalidates any values the compiler might have cached for the atomic_read. 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/