Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757063AbXITPK1 (ORCPT ); Thu, 20 Sep 2007 11:10:27 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1755309AbXITPKT (ORCPT ); Thu, 20 Sep 2007 11:10:19 -0400 Received: from outbound-mail-28.bluehost.com ([69.89.17.198]:42789 "HELO outbound-mail-28.bluehost.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with SMTP id S1755228AbXITPKR (ORCPT ); Thu, 20 Sep 2007 11:10:17 -0400 X-Greylist: delayed 400 seconds by postgrey-1.27 at vger.kernel.org; Thu, 20 Sep 2007 11:10:17 EDT From: Jesse Barnes To: Andi Kleen Subject: Re: MTRR initialization Date: Thu, 20 Sep 2007 08:03:31 -0700 User-Agent: KMail/1.9.7 Cc: Jesse Barnes , Howard Chu , linux-kernel References: <46EAB7DA.10507@symas.com> <200709191452.57505.jesse.barnes@intel.com> In-Reply-To: MIME-Version: 1.0 Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: 7bit Content-Disposition: inline Message-Id: <200709200803.31795.jbarnes@virtuousgeek.org> X-Identified-User: {642:box128.bluehost.com:virtuous:virtuousgeek.org} {sentby:smtp auth 76.103.130.182 authed with jbarnes@virtuousgeek.org} X-AntiAbuse: This header was added to track abuse, please include it with any abuse report X-AntiAbuse: Primary Hostname - box128.bluehost.com X-AntiAbuse: Original Domain - vger.kernel.org X-AntiAbuse: Originator/Caller UID/GID - [642 12] / [47 12] X-AntiAbuse: Sender Address Domain - virtuousgeek.org Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1112 Lines: 23 On Wednesday, September 19, 2007 11:50:23 pm Andi Kleen wrote: > Jesse Barnes writes: > > To do this in a nicer way (and be less vulnerable to similar BIOS > > funkiness) the kernel really needs full PAT support. That should allow > > WC over WB and WC over UC mappings to occur, at least if I'm > > remembering the docs right... > > PAT only really helps for device driver performance optimizations. > But if the basic WB MTRRs are wrong PAT cannot really salvage it. Look at the original bug report. There's a bug WB region so any subsequent WC mappings via the MTRRs won't work, so you need PAT to do WC (unless you want to rewrite all your MTRR settings as Howard has to do now). Seems like more and more machines are being setup this way, and until we have PAT users will have to jump through hoops to get good performance. Jesse - 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/