Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754418AbaBRDZA (ORCPT ); Mon, 17 Feb 2014 22:25:00 -0500 Received: from mail-vc0-f177.google.com ([209.85.220.177]:36853 "EHLO mail-vc0-f177.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753027AbaBRDY6 (ORCPT ); Mon, 17 Feb 2014 22:24:58 -0500 MIME-Version: 1.0 In-Reply-To: <20140218030002.GA15857@linux.vnet.ibm.com> References: <1392321837.18779.3249.camel@triegel.csb> <20140214020144.GO4250@linux.vnet.ibm.com> <1392352981.18779.3800.camel@triegel.csb> <20140214172920.GQ4250@linux.vnet.ibm.com> <1392486310.18779.6447.camel@triegel.csb> <1392666947.18779.6838.camel@triegel.csb> <20140218030002.GA15857@linux.vnet.ibm.com> Date: Mon, 17 Feb 2014 19:24:56 -0800 X-Google-Sender-Auth: -7WnL_9rQFOeDjtG18h5WMKezhk Message-ID: Subject: Re: [RFC][PATCH 0/5] arch: atomic rework From: Linus Torvalds To: Paul McKenney Cc: Torvald Riegel , Will Deacon , Peter Zijlstra , Ramana Radhakrishnan , David Howells , "linux-arch@vger.kernel.org" , "linux-kernel@vger.kernel.org" , "akpm@linux-foundation.org" , "mingo@kernel.org" , "gcc@gcc.gnu.org" Content-Type: text/plain; charset=UTF-8 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Feb 17, 2014 at 7:00 PM, Paul E. McKenney wrote: > > One example that I learned about last week uses the branch-prediction > hardware to validate value speculation. And no, I am not at all a fan > of value speculation, in case you were curious. Heh. See the example I used in my reply to Alec Teal. It basically broke the same dependency the same way. Yes, value speculation of reads is simply wrong, the same way speculative writes are simply wrong. The dependency chain matters, and is meaningful, and breaking it is actively bad. As far as I can tell, the intent is that you can't do value speculation (except perhaps for the "relaxed", which quite frankly sounds largely useless). But then I do get very very nervous when people talk about "proving" certain values. Linus -- 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/