From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1760165AbYGVXfq (ORCPT ); Tue, 22 Jul 2008 19:35:46 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1759067AbYGVX2Y (ORCPT ); Tue, 22 Jul 2008 19:28:24 -0400 Received: from srv5.dvmed.net ([207.36.208.214]:54957 "EHLO mail.dvmed.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1758416AbYGVX2W (ORCPT ); Tue, 22 Jul 2008 19:28:22 -0400 Message-ID: <48866D10.3020907@garzik.org> Date: Tue, 22 Jul 2008 19:28:16 -0400 From: Jeff Garzik User-Agent: Thunderbird 2.0.0.14 (X11/20080501) MIME-Version: 1.0 To: "H. Peter Anvin" 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> <488629D5.4050603@zytor.com> In-Reply-To: <488629D5.4050603@zytor.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Spam-Score: -4.4 (----) X-Spam-Report: SpamAssassin version 3.2.5 on srv5.dvmed.net summary: Content analysis details: (-4.4 points, 5.0 required) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org H. Peter Anvin wrote: > 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.) It's generally more an issue of making sure the compiler is not instructed to issue cmov (-march=i686). > 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. Yeah. Jeff