linux-kernel - Re: 2.6.27rc1 cannot boot more than 8CPUs

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Date:	Wed, 13 Aug 2008 11:33:12 -0700
From:	"Yinghai Lu" <yhlu.kernel@...il.com>
To:	"Ingo Molnar" <mingo@...e.hu>,
	"Jeff Chua" <jeff.chua.linux@...il.com>
Cc:	"David Miller" <davem@...emloft.net>,
	"Linux Kernel" <linux-kernel@...r.kernel.org>
Subject: Re: 2.6.27rc1 cannot boot more than 8CPUs

On Wed, Aug 13, 2008 at 10:46 AM, Yinghai Lu <yhlu.kernel@...il.com> wrote:
> On Wed, Aug 13, 2008 at 10:39 AM, Ingo Molnar <mingo@...e.hu> wrote:
>>
>> * Jeff Chua <jeff.chua.linux@...il.com> wrote:
>>
>>> On Thu, Aug 14, 2008 at 1:10 AM, Jeff Chua <jeff.chua.linux@...il.com> wrote:
>>> > On Wed, Aug 13, 2008 at 10:16 PM, Ingo Molnar <mingo@...e.hu> wrote:
>>> >
>>> >> btw., could you please check that v2.6.27-rc3 (or later) kernels boot
>>> >> fine (with about 8 cpus) even if you have genericarch/bigsmp disabled,
>>> >> and do not silently hang as it happened on your box before?
>>> >
>>> > With 16 CPUs, it still hangs, but now the console is showing the
>>> > errors as intended.
>>> > ... but it is supposed to hang?
>>>
>>> I tried with just CONFIG_NR_CPUS=8 and this time it booted, but stange
>>> thing is I only see 2 CPUs! To be more precise, it's without both
>>> CONFIG_X86_GENERICARCH and CONFIG_X86_BIGSMP.
>>>
>>> And when I tried to enable the CPUs, it complained about:
>>>
>>> # cat cpu6/online
>>> 0
>>> # echo 1 > cpu6/online
>>> More than 8 CPUs detected - skipping them.
>>> Use CONFIG_X86_GENERICARCH and CONFIG_X86_BIGSMP.
>>> -bash: echo: write error: Input/output error
>>>
>>> Prior to the patch, the system booted with all 8 CPUs.
>
> that is new regression...

jeff,

please check the attached patch. it should fix the new regression and
will not hang.

YH

View attachment "big_smp_check.patch" of type "text/x-patch" (1839 bytes)