Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1765924AbXJRRGW (ORCPT ); Thu, 18 Oct 2007 13:06:22 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1763773AbXJRRGM (ORCPT ); Thu, 18 Oct 2007 13:06:12 -0400 Received: from artax.karlin.mff.cuni.cz ([195.113.31.125]:39124 "EHLO artax.karlin.mff.cuni.cz" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756776AbXJRRGL (ORCPT ); Thu, 18 Oct 2007 13:06:11 -0400 Date: Thu, 18 Oct 2007 19:06:09 +0200 (CEST) From: Mikulas Patocka To: Nick Piggin cc: Arjan van de Ven , Linux Kernel Mailing List Subject: Re: LFENCE instruction (was: [rfc][patch 3/3] x86: optimise barriers) In-Reply-To: <20071017122435.GA14401@wotan.suse.de> Message-ID: References: <20071015143732.01d99af8@laptopd505.fenrus.org> <20071016002229.GA5851@wotan.suse.de> <20071016222921.GA29378@wotan.suse.de> <20071016232153.GC29378@wotan.suse.de> <20071017122435.GA14401@wotan.suse.de> X-Personality-Disorder: Schizoid 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: 1024 Lines: 29 > > > > You already must not place any data structures into WC memory --- for > > > > example, spinlocks wouldn't work there. > > > > > > What do you mean "already"? > > > > I mean "in current kernel" (I checked it in 2.6.22) > > Ahh, that's not "current kernel", though ;) > > 4071c718555d955a35e9651f77086096ad87d498 > > > So drivers can't assume that wmb() works on write-combining memory. > > Drivers should be able to assume that wmb() orders _everything_ (except > some whacky Altix thing, which I really want to fold under wmb at some > point anyway). > > So I decided that old x86 semantics isn't right, and now it really is a > lock op / sfence everywhere. I see. I'm just curious --- is there any real usage for WC memory, except graphics card memory? Mikulas - 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/