From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754881AbYIHPiZ (ORCPT ); Mon, 8 Sep 2008 11:38:25 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1753372AbYIHPh6 (ORCPT ); Mon, 8 Sep 2008 11:37:58 -0400 Received: from terminus.zytor.com ([198.137.202.10]:38442 "EHLO terminus.zytor.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753231AbYIHPh5 (ORCPT ); Mon, 8 Sep 2008 11:37:57 -0400 Message-ID: <48C54690.1060002@zytor.com> Date: Mon, 08 Sep 2008 08:36:48 -0700 From: "H. Peter Anvin" User-Agent: Thunderbird 2.0.0.14 (X11/20080501) MIME-Version: 1.0 To: Ingo Molnar CC: Linus Torvalds , linux@sandersweb.net, linux-kernel@vger.kernel.org, the arch/x86 maintainers , Andi Kleen Subject: Re: [BUG] x86 kenel won't boot under Virtual PC References: <200808311422.12525.linux@sandersweb.net> <200809071922.32974.linux@sandersweb.net> <48C48467.40703@zytor.com> <200809072249.17280.linux@sandersweb.net> <48C4A46B.90705@zytor.com> <20080908152330.GA9784@elte.hu> In-Reply-To: <20080908152330.GA9784@elte.hu> 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 Ingo Molnar wrote: > > yes. X86_P6_NOPS is a totally insignificant optimization and if it makes > _any_ CPU not boot (be that virtual or real), then it's frankly not > worth it. > > David, exactly how does the kernel fail to boot with latest -git? > (v2.6.27-rc5-313-g64f996f or later) Does detect_nopl() run? It really > should, and it should detect the non-working instructions. > Okay, a few things here... 1. First, I wrote up a patch yesterday to update the CONFIG_X86_GENERIC description and to make it "default y". It is currently on x86/defconfig, but I think it should be promoted to mainline immediately. 2. X86_P6_NOPS is not the only source of static NOPLs. If gcc is set to optimize for specific architectures, then gcc/binutils will generate static NOPLs. The only way we can prevent that is by not using specific -march options, as far as I can tell. 3. I'm not positive that CONFIG_X86_GENERIC currently avoid all cases of (2), but it obviously should. I will verify that today and add a followup patch to the Makefiles if necessary. Given all of this, I really think that putting this on CONFIG_X86_GENERIC, *AND* making CONFIG_X86_GENERIC the default is the right choice. -hpa