Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752350Ab3FWUDG (ORCPT ); Sun, 23 Jun 2013 16:03:06 -0400 Received: from terminus.zytor.com ([198.137.202.10]:42423 "EHLO mail.zytor.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750923Ab3FWUDE (ORCPT ); Sun, 23 Jun 2013 16:03:04 -0400 Message-ID: <51C75465.9060007@zytor.com> Date: Sun, 23 Jun 2013 13:02:45 -0700 From: "H. Peter Anvin" User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:17.0) Gecko/20130514 Thunderbird/17.0.6 MIME-Version: 1.0 To: Henrique de Moraes Holschuh CC: Brice Goglin , Linux Kernel Mailing List , David Airlie , dri-devel@lists.freedesktop.org Subject: Re: MTRR use in drivers References: <51C3DDFA.7050204@zytor.com> <51C69732.1010906@gmail.com> <20130623192936.GA28655@khazad-dum.debian.net> In-Reply-To: <20130623192936.GA28655@khazad-dum.debian.net> X-Enigmail-Version: 1.5.1 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1237 Lines: 29 On 06/23/2013 12:29 PM, Henrique de Moraes Holschuh wrote: > On Sun, 23 Jun 2013, H. Peter Anvin wrote: >> Why do you care about performance when PAT is disabled? > > It will regress already slow boxes. We blacklist a LOT of P4s, PMs, etc and > nobody ever took the pain to track down which ones of those actually have > PAT+MTRR aliasing bugs. > > These boxes have boards like the Radeon X300, which needs either PAT or MTRR > to not become unusable... > We're talking hardware which is now many years old, but this is causing very serious problems on real, modern hardware. As far as I understand it, too, the blacklisting was precautionary (the only bug that I personally know about is a performance bug, where WC would be incorrectly converted to UC.) We need a way forward here. If it is the only way I think we would have to sacrifice the old machines, but perhaps something can be worked out (e.g. if PAT is disabled, fall back to MTRRs if available for ioremap_wc()). -hpa -- 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/