Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755891Ab1DGQmu (ORCPT ); Thu, 7 Apr 2011 12:42:50 -0400 Received: from one.firstfloor.org ([213.235.205.2]:44737 "EHLO one.firstfloor.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753860Ab1DGQms (ORCPT ); Thu, 7 Apr 2011 12:42:48 -0400 Date: Thu, 7 Apr 2011 18:42:45 +0200 From: Andi Kleen To: Linus Torvalds Cc: Andy Lutomirski , x86@kernel.org, Thomas Gleixner , Ingo Molnar , Andi Kleen , linux-kernel@vger.kernel.org Subject: Re: [RFT/PATCH v2 2/6] x86-64: Optimize vread_tsc's barriers Message-ID: <20110407164245.GA21838@one.firstfloor.org> References: <80b43d57d15f7b141799a7634274ee3bfe5a5855.1302137785.git.luto@mit.edu> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.4.2.2i Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 822 Lines: 21 > But before that, I would check that the second lfence is needed AT > ALL. I don't know whether we ever tried the "only barrier before" > version, because quite frankly, if you call this thing in a loop, then > a single barrier will still mean that there are barriers in between > iterations. So... The testers will call it in a loop, but real users (e.g. using it for a logging timestamp) may not. I'm sure a single barrier would have fixed the testers, as you point out, but the goal wasn't to only fix testers. -Andi -- ak@linux.intel.com -- Speaking for myself only. -- 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/