From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756715AbbJARSo (ORCPT ); Thu, 1 Oct 2015 13:18:44 -0400 Received: from bombadil.infradead.org ([198.137.202.9]:56673 "EHLO bombadil.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753784AbbJARSn (ORCPT ); Thu, 1 Oct 2015 13:18:43 -0400 Date: Thu, 1 Oct 2015 19:13:04 +0200 From: Peter Zijlstra To: "Paul E. McKenney" Cc: Boqun Feng , linux-kernel@vger.kernel.org, linuxppc-dev@lists.ozlabs.org, Ingo Molnar , Benjamin Herrenschmidt , Paul Mackerras , Michael Ellerman , Thomas Gleixner , Will Deacon , Waiman Long Subject: Re: [RFC v2 4/7] powerpc: atomic: Implement xchg_* and atomic{,64}_xchg_* variants Message-ID: <20151001171304.GX3816@twins.programming.kicks-ass.net> References: <1442418575-12297-1-git-send-email-boqun.feng@gmail.com> <1442418575-12297-5-git-send-email-boqun.feng@gmail.com> <20151001122440.GP2881@worktop.programming.kicks-ass.net> <20151001150909.GC4043@linux.vnet.ibm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20151001150909.GC4043@linux.vnet.ibm.com> User-Agent: Mutt/1.5.21 (2012-12-30) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Oct 01, 2015 at 08:09:09AM -0700, Paul E. McKenney wrote: > On Thu, Oct 01, 2015 at 02:24:40PM +0200, Peter Zijlstra wrote: > > I must say I'm somewhat surprised by this level of relaxation, I had > > expected to only loose SMP barriers, not the program order ones. > > > > Is there a good argument for this? > > Yes, when we say "relaxed", we really mean relaxed. ;-) > > Both the CPU and the compiler are allowed to reorder around relaxed > operations. Is this documented somewhere, because I completely missed this part.