From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755467AbYGVSmT (ORCPT ); Tue, 22 Jul 2008 14:42:19 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1752670AbYGVSmH (ORCPT ); Tue, 22 Jul 2008 14:42:07 -0400 Received: from terminus.zytor.com ([198.137.202.10]:34260 "EHLO terminus.zytor.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751417AbYGVSmG (ORCPT ); Tue, 22 Jul 2008 14:42:06 -0400 Message-ID: <488629D5.4050603@zytor.com> Date: Tue, 22 Jul 2008 14:41:25 -0400 From: "H. Peter Anvin" User-Agent: Thunderbird 2.0.0.14 (X11/20080501) MIME-Version: 1.0 To: Jeff Garzik CC: "Luis R. Rodriguez" , linux kernel , "H. Peter Anvin" , Ivan Seskar , jfm3 , Sujith Subject: Re: Bug on 2.6.26 - x86 VIA Nehemiah CentaurHauls processor cannot boot References: <43e72e890807210614y58065d75j5b2fb3c5ebe6180a@mail.gmail.com> <48848DDF.6010903@zytor.com> <43e72e890807210701w6d7f5638w5fdbea76a1cf1c0b@mail.gmail.com> <48851AC2.8030007@zytor.com> <43e72e890807212147p5d19cfact17e719abb338378c@mail.gmail.com> <488614A3.1060400@garzik.org> <48862526.7060704@zytor.com> <488627E2.2060101@garzik.org> In-Reply-To: <488627E2.2060101@garzik.org> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Jeff Garzik wrote: > >> We're only referring specifically to the family == 6 VIA processors here. > > To be specific, I was merely saying that VIA processors where > c->x86_model==6 may lack CMOV. > > I have not kept track of what current Kconfig options will set, but in > the past it was quite easy to build a "generic 686 kernel" that required > CMOV and thus excluded these VIA processors. > > Distros in the past often wound up intentionally -not- supporting some > of these VIA processors, because they did not want to create a non-CMOV > kernel. (This policy obviously excluded older x86 as well) > > If these things have been addressed recently (< 12-18 months) then all > good. > I am pretty sure CONFIG_X86_GENERIC doesn't disable CMOV, and since CMOV is a separate CPUID flag it's all good (if the chip doesn't have it, it'll trap.) Unfortunately Intel didn't assign a CPUID flag for the long NOPs, and then didn't document them (I think partially because they were a retcon), but yet it reflected a serious hole in Centaur's characterization effort that they bumped family to 6 without following P6 behaviour for a massive range of opcodes. The main reason for disabling P6 NOPs for CONFIG_X86_GENERIC is that the win is so small, and that a number of vendors got it wrong. -hpa