linux-kernel - Re: [regression 2.6.27.10 & 2.6.28] \"nolapic\" option causes \"nosmp\"?

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Message-ID: <alpine.LFD.1.10.0901052156460.10676@ftp.linux-mips.org>
Date:	Mon, 5 Jan 2009 22:07:25 +0000 (GMT)
From:	"Maciej W. Rozycki" <macro@...ux-mips.org>
To:	Tetsuo Handa <penguin-kernel@...ove.sakura.ne.jp>
cc:	linux-kernel@...r.kernel.org, hpa@...or.com
Subject: Re: [regression 2.6.27.10 & 2.6.28] \"nolapic\" option causes
 \"nosmp\"?

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
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