Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752875AbaBGSp3 (ORCPT ); Fri, 7 Feb 2014 13:45:29 -0500 Received: from mx1.redhat.com ([209.132.183.28]:13896 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751446AbaBGSp2 (ORCPT ); Fri, 7 Feb 2014 13:45:28 -0500 Subject: Re: [RFC][PATCH 0/5] arch: atomic rework From: Torvald Riegel To: paulmck@linux.vnet.ibm.com Cc: Peter Zijlstra , Will Deacon , Ramana Radhakrishnan , David Howells , "linux-arch@vger.kernel.org" , "linux-kernel@vger.kernel.org" , "torvalds@linux-foundation.org" , "akpm@linux-foundation.org" , "mingo@kernel.org" , "gcc@gcc.gnu.org" In-Reply-To: <20140207165028.GO4250@linux.vnet.ibm.com> References: <20140206134825.305510953@infradead.org> <21984.1391711149@warthog.procyon.org.uk> <52F3DA85.1060209@arm.com> <20140206185910.GE27276@mudshark.cambridge.arm.com> <20140206192743.GH4250@linux.vnet.ibm.com> <1391721423.23421.3898.camel@triegel.csb> <20140206221117.GJ4250@linux.vnet.ibm.com> <1391730288.23421.4102.camel@triegel.csb> <20140207042051.GL4250@linux.vnet.ibm.com> <20140207074405.GM5002@laptop.programming.kicks-ass.net> <20140207165028.GO4250@linux.vnet.ibm.com> Content-Type: text/plain; charset="UTF-8" Date: Fri, 07 Feb 2014 19:44:56 +0100 Message-ID: <1391798696.23421.4805.camel@triegel.csb> Mime-Version: 1.0 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, 2014-02-07 at 08:50 -0800, Paul E. McKenney wrote: > On Fri, Feb 07, 2014 at 08:44:05AM +0100, Peter Zijlstra wrote: > > On Thu, Feb 06, 2014 at 08:20:51PM -0800, Paul E. McKenney wrote: > > > Hopefully some discussion of out-of-thin-air values as well. > > > > Yes, absolutely shoot store speculation in the head already. Then drive > > a wooden stake through its hart. > > > > C11/C++11 should not be allowed to claim itself a memory model until that > > is sorted. > > There actually is a proposal being put forward, but it might not make ARM > and Power people happy because it involves adding a compare, a branch, > and an ISB/isync after every relaxed load... Me, I agree with you, > much preferring the no-store-speculation approach. My vague recollection is that everyone agrees that out-of-thin-air values shouldn't be allowed, but that it's surprisingly complex to actually specify this properly. However, the example that Peter posted further down in the thread seems to be unrelated to out-of-thin-air. -- 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/