From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S934231AbaFQQ2Z (ORCPT ); Tue, 17 Jun 2014 12:28:25 -0400 Received: from qmta13.emeryville.ca.mail.comcast.net ([76.96.27.243]:55355 "EHLO qmta13.emeryville.ca.mail.comcast.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S933404AbaFQQ2W (ORCPT ); Tue, 17 Jun 2014 12:28:22 -0400 Date: Tue, 17 Jun 2014 11:28:19 -0500 (CDT) From: Christoph Lameter To: Tejun Heo cc: "Paul E. McKenney" , David Howells , Linus Torvalds , Andrew Morton , Oleg Nesterov , linux-kernel@vger.kernel.org, Rusty Russell Subject: Re: [PATCH RFC] percpu: add data dependency barrier in percpu accessors and operations In-Reply-To: <20140617160508.GF31819@htj.dyndns.org> Message-ID: References: <20140612135630.GA23606@htj.dyndns.org> <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> Content-Type: TEXT/PLAIN; charset=US-ASCII Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, 17 Jun 2014, Tejun Heo wrote: > On Tue, Jun 17, 2014 at 12:00:40PM -0400, Tejun Heo wrote: > > Hello, Christoph. > > > > On Tue, Jun 17, 2014 at 10:56:10AM -0500, Christoph Lameter wrote: > > > Uhhh no. The percpu stuff and the associated per cpu atomics are to be > > > used for stuff that is per cpu specific and runs at the fastest speed > > > doable at that level. Introducing implicit barriers is not that good an > > > idea. > > > > Hmmm? Read barriers are noops on all archs except for alpha and > > Oops, data dependency barriers, not read barrier. Even alpha maintains the illusion of changes becoming visible in the proper order for the currently executing thread. No barriers are needed.