From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754735AbZAEWHi (ORCPT ); Mon, 5 Jan 2009 17:07:38 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1753374AbZAEWH1 (ORCPT ); Mon, 5 Jan 2009 17:07:27 -0500 Received: from ftp.linux-mips.org ([213.58.128.207]:52575 "EHLO ftp.linux-mips.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752977AbZAEWH1 (ORCPT ); Mon, 5 Jan 2009 17:07:27 -0500 Date: Mon, 5 Jan 2009 22:07:25 +0000 (GMT) From: "Maciej W. Rozycki" To: Tetsuo Handa cc: linux-kernel@vger.kernel.org, hpa@zytor.com Subject: Re: [regression 2.6.27.10 & 2.6.28] \"nolapic\" option causes \"nosmp\"? In-Reply-To: <200901050318.n053Iu0L068557@www262.sakura.ne.jp> Message-ID: References: <200901050318.n053Iu0L068557@www262.sakura.ne.jp> 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 Mon, 5 Jan 2009, Tetsuo Handa wrote: > Adding "nolapic" option to kernel command line causes /proc/cpuinfo to show > only 1 CPU, while the machine has 2 CPUs and the kernel was compiled with > CONFIG_SMP=y. > > Something is wrong with CPU recognition/initialization code? This is correct behaviour. The hardware uses the local APIC to communicate between CPUs. With the subsystem disabled there is no way to reach secondary CPUs on a standard x86 system. > This topic is continued from http://lkml.org/lkml/2008/12/30/104 . > I confirmed that this problem occurs on native Ubuntu 8.04 (i386) and > native CentOS 5.2 (x86_64) on ThinkPad X60 (Core 2 Duo). > > Kernel 2.6.26.8 seems to be OK. If this is the case, then "nolapic" must have been dysfunctional in that version of the kernel. Maciej