Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751372AbWARRGn (ORCPT ); Wed, 18 Jan 2006 12:06:43 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1751375AbWARRGn (ORCPT ); Wed, 18 Jan 2006 12:06:43 -0500 Received: from vanessarodrigues.com ([192.139.46.150]:54677 "EHLO jaguar.mkp.net") by vger.kernel.org with ESMTP id S1751372AbWARRGm (ORCPT ); Wed, 18 Jan 2006 12:06:42 -0500 To: "Bryan O'Sullivan" Cc: Andi Kleen , linux-kernel@vger.kernel.org, discuss@x86-64.org Subject: Re: Why is wmb() a no-op on x86_64? References: <1137601417.4757.38.camel@serpentine.pathscale.com> <200601181729.36423.ak@suse.de> <1137603169.4757.50.camel@serpentine.pathscale.com> From: Jes Sorensen Date: 18 Jan 2006 12:06:39 -0500 In-Reply-To: <1137603169.4757.50.camel@serpentine.pathscale.com> Message-ID: User-Agent: Gnus/5.09 (Gnus v5.9.0) Emacs/21.4 MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 874 Lines: 17 >>>>> "Bryan" == Bryan O'Sullivan writes: Bryan> On Wed, 2006-01-18 at 17:29 +0100, Andi Kleen wrote: >> Why do you need the barrier? Bryan> On x86_64, we fiddle with the MTRRs to enable write combining, Bryan> which makes a huge difference to performance. It's not clear Bryan> to me what we should even do on other architectures, since the Bryan> only generic entry point that even exposes write combining is Bryan> pci_mmap_page_range, which is for PCI mmap through userspace, Bryan> and half the arches I've looked at ignore its write_combine Bryan> parameter. A job for mmiowb() perhaps? Cheers, Jes - 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/