From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755966AbYEFLtJ (ORCPT ); Tue, 6 May 2008 07:49:09 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1752181AbYEFLsz (ORCPT ); Tue, 6 May 2008 07:48:55 -0400 Received: from mx2.mail.elte.hu ([157.181.151.9]:52952 "EHLO mx2.mail.elte.hu" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752138AbYEFLsz (ORCPT ); Tue, 6 May 2008 07:48:55 -0400 Date: Tue, 6 May 2008 13:48:39 +0200 From: Ingo Molnar To: Mikael Pettersson Cc: tglx@linutronix.de, mingo@redhat.com, hpa@zytor.com, venkatesh.pallipadi@intel.com, linux-kernel@vger.kernel.org Subject: Re: 2.6.26-rc1 lies about PAT not being available Message-ID: <20080506114839.GD32591@elte.hu> References: <18464.5177.649312.999486@harpo.it.uu.se> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <18464.5177.649312.999486@harpo.it.uu.se> User-Agent: Mutt/1.5.17 (2007-11-01) X-ELTE-VirusStatus: clean X-ELTE-SpamScore: -1.5 X-ELTE-SpamLevel: X-ELTE-SpamCheck: no X-ELTE-SpamVersion: ELTE 2.0 X-ELTE-SpamCheck-Details: score=-1.5 required=5.9 tests=BAYES_00 autolearn=no SpamAssassin version=3.2.3 -1.5 BAYES_00 BODY: Bayesian spam probability is 0 to 1% [score: 0.0000] Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org * Mikael Pettersson wrote: > Booting 2.6.26-rc1 on an old Coppermine PIII, I'm greeted with: > > >Linux version 2.6.26-rc1 (mikpe@dryhop) (gcc version 4.2.3) #1 Mon May 5 21:49:49 CEST 2008 > >BIOS-provided physical RAM map: > > BIOS-e820: 0000000000000000 - 000000000009c000 (usable) > > BIOS-e820: 000000000009c000 - 00000000000a0000 (reserved) > > BIOS-e820: 00000000000f0000 - 0000000000100000 (reserved) > > BIOS-e820: 0000000000100000 - 000000002ffec000 (usable) > > BIOS-e820: 000000002ffec000 - 000000002ffef000 (ACPI data) > > BIOS-e820: 000000002ffef000 - 000000002ffff000 (reserved) > > BIOS-e820: 000000002ffff000 - 0000000030000000 (ACPI NVS) > > BIOS-e820: 00000000ffff0000 - 0000000100000000 (reserved) > >CPU and/or kernel does not support PAT. > > I know about Intel's PAT erratum (only 4 PAT entries work) and > understand that the kernel might not want to use a half-broken PAT > implementation, but the statement above is blatantly false: the kernel > IS built with PAT support and the CPU DOES have (half-broken) PAT HW > support as /proc/cpuinfo from earlier kernels confirms. well the code is just being overly conservative, and the message is right: the kernel does not support PAT on that hw. Yet. Please send us a patch and test whether it's working on your box? That's how the PAT code evolved: it initially was only enabled on a very small subset of CPUs. We can enable it on more CPUs if people test it. To be conservative, please make the code emit a printk that this is PAT on not fully-working hw platform (only 4 PAT entries work). If there _is_ some erratum on that CPU affecting PAT reliability down the line, we at least want to have some clue in the syslog. Ingo