From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752821AbYIEQb2 (ORCPT ); Fri, 5 Sep 2008 12:31:28 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1751097AbYIEQbT (ORCPT ); Fri, 5 Sep 2008 12:31:19 -0400 Received: from smtp1.linux-foundation.org ([140.211.169.13]:53183 "EHLO smtp1.linux-foundation.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750989AbYIEQbT (ORCPT ); Fri, 5 Sep 2008 12:31:19 -0400 Date: Fri, 5 Sep 2008 09:30:14 -0700 (PDT) From: Linus Torvalds To: David Sanders cc: linux-kernel@vger.kernel.org, Arjan van de Ven , Jan Beulich , Ingo Molnar , Thomas Gleixner , Andi Kleen Subject: Re: [BUG] x86 kenel won't boot under Virtual PC In-Reply-To: <200809051138.20615.linux@sandersweb.net> Message-ID: References: <200808311422.12525.linux@sandersweb.net> <20080831122751.72afafb5@infradead.org> <200809051138.20615.linux@sandersweb.net> User-Agent: Alpine 1.10 (LFD 962 2008-03-14) MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, 5 Sep 2008, David Sanders wrote: > > The patch disables a optimization used in one place by commenting out some > lines in nop.h. Please comment. Hmm.. I'm not a huge fan of the ASM_NOP mess, but you also disable it for 64-bit x86 too. On 32-bit, at least the generic nops are fairly reasonable, but the default nops for 64-bit really look pretty sad, and the P6 nops really do look better. So I would suggest perhaps moving the static P6 nop selection into the CONFIG_X86_64 thing. The alternative is to just get rid of that static nop selection, and just have two cases: 32-bit and 64-bit, and just pick obviously safe cases for them. So I think that particular part would be better off with changing the Kconfig language instead. Ie something like this.. (I removed the 32-bit CPU's from the choices, except for MPENTIUM4 that really should be merged with MPSC - the difference between MPENTIUM4 and MPSC seems to be just a totally bogus 32-bit vs 64-bit thing. Yes, yes, there are PENTIUM4's without 64-bit, but there are also Prescott chips that run 32-bit kernels, so the thing is a bit confused. Linus --- arch/x86/Kconfig.cpu | 13 ++++++++----- 1 files changed, 8 insertions(+), 5 deletions(-) diff --git a/arch/x86/Kconfig.cpu b/arch/x86/Kconfig.cpu index 2c518fb..b225219 100644 --- a/arch/x86/Kconfig.cpu +++ b/arch/x86/Kconfig.cpu @@ -382,14 +382,17 @@ config X86_OOSTORE # P6_NOPs are a relatively minor optimization that require a family >= # 6 processor, except that it is broken on certain VIA chips. # Furthermore, AMD chips prefer a totally different sequence of NOPs -# (which work on all CPUs). As a result, disallow these if we're -# compiling X86_GENERIC but not X86_64 (these NOPs do work on all -# x86-64 capable chips); the list of processors in the right-hand clause -# are the cores that benefit from this optimization. +# (which work on all CPUs). In addition, it looks like Virtual PC +# does not understand them. +# +# As a result, disallow these if we're not compiling for X86_64 (these +# NOPs do work on all x86-64 capable chips); the list of processors in +# the right-hand clause are the cores that benefit from this optimization. # config X86_P6_NOP def_bool y - depends on (X86_64 || !X86_GENERIC) && (M686 || MPENTIUMII || MPENTIUMIII || MPENTIUMM || MCORE2 || MPENTIUM4 || MPSC) + depends on X86_64 + depends on (MCORE2 || MPENTIUM4 || MPSC) config X86_TSC def_bool y