Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756206AbaFQSzT (ORCPT ); Tue, 17 Jun 2014 14:55:19 -0400 Received: from e31.co.us.ibm.com ([32.97.110.149]:37243 "EHLO e31.co.us.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755642AbaFQSzR (ORCPT ); Tue, 17 Jun 2014 14:55:17 -0400 Date: Tue, 17 Jun 2014 11:55:10 -0700 From: "Paul E. McKenney" To: Christoph Lameter Cc: Linus Torvalds , Rusty Russell , Andrew Morton , Tejun Heo , David Howells , linux-kernel@vger.kernel.org, Oleg Nesterov Subject: Re: [PATCH RFC] percpu: add data dependency barrier in percpu accessors and operations Message-ID: <20140617185510.GM4669@linux.vnet.ibm.com> Reply-To: paulmck@linux.vnet.ibm.com References: <20140612153426.GV4581@linux.vnet.ibm.com> <20140612155227.GB23606@htj.dyndns.org> <20140617144151.GD4669@linux.vnet.ibm.com> <20140617152752.GC31819@htj.dyndns.org> <20140617160040.GE31819@htj.dyndns.org> <20140617160508.GF31819@htj.dyndns.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.21 (2010-09-15) X-TM-AS-MML: disable X-Content-Scanned: Fidelis XPS MAILER x-cbid: 14061718-8236-0000-0000-0000032BE50D Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Jun 17, 2014 at 01:47:01PM -0500, Christoph Lameter wrote: > > On Tue, 17 Jun 2014, Linus Torvalds wrote: > > > On Jun 17, 2014 6:28 AM, "Christoph Lameter" wrote: > > > > > > Even alpha maintains the illusion of changes becoming visible in the > > > proper order for the currently executing thread. No barriers are needed. > > > > No Christoph, alpha really doesn't. Barriers needed. > > Everythig breaks if a single hardware execution thread can no longer > observe a consistent view of the world of the data it modifies. > > We are not talking about synchronization here between multiple hardware > threads. This is simply code running on a single hardware thread and all > architectures maintain the uniprocessor illusion there. We are talking about one CPU initializing all CPUs' portions of dynamically allocated per-CPU memory, so there really is more than one CPU involved. Thanx, Paul -- 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/