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

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Message-ID: <86802c440808111312n49ce2c0akae18b539ad543410@mail.gmail.com>
Date:	Mon, 11 Aug 2008 13:12:14 -0700
From:	"Yinghai Lu" <yhlu.kernel@...il.com>
To:	"Ingo Molnar" <mingo@...e.hu>
Cc:	"Jeff Chua" <jeff.chua.linux@...il.com>,
	"Linus Torvalds" <torvalds@...ux-foundation.org>,
	"David Miller" <davem@...emloft.net>,
	"Max Krasnyansky" <maxk@...lcomm.com>,
	"Li Zefan" <lizf@...fujitsu.com>,
	lkml <linux-kernel@...r.kernel.org>
Subject: Re: 2.6.27rc1 cannot boot more than 8CPUs

On Mon, Aug 11, 2008 at 1:08 PM, Ingo Molnar <mingo@...e.hu> wrote:
>
> * Yinghai Lu <yhlu.kernel@...il.com> wrote:
>
>> On Mon, Aug 11, 2008 at 12:59 PM, Ingo Molnar <mingo@...e.hu> wrote:
>> >
>> > * Jeff Chua <jeff.chua.linux@...il.com> wrote:
>> >
>> >> On Wed, Aug 6, 2008 at 2:42 PM, Jeff Chua <jeff.chua.linux@...il.com> wrote:
>> >> > On Wed, Aug 6, 2008 at 2:01 PM, Linus Torvalds
>> >> > <torvalds@...ux-foundation.org> wrote:
>> >> >> One trivial thing to try would be to just bisect it. I assume 2.6.26 is
>> >> > Bisecting now.
>> >>
>> >> Thanks to all the great helpful suggestions from everyone, and this
>> >> turns out that I just need to enable the following switches, so I
>> >> didn't bisect further, and since it's first machine that I've tried
>> >> with more than 8 CPUs so I wasn't sure whether 2.6.16 has the same
>> >> problem, but if you wish, I could give 2.6.16 a try.
>> >>
>> >> > CONFIG_X86_GENERICARCH=y
>> >> > CONFIG_X86_BIGSMP=y
>> >>
>> >> Thank you all for the great linux kernel!
>> >
>> > i still consider a silent boot hang a bug we need to fix.
>> >
>> > bigsmp might be required to have all cpus available on your box, but the
>> > kernel is still supposed to transparently fall back to less CPUs (and
>> > print a warning) if it cannot do that.
>> >
>> in setup.c::setup_arch() after go over with madt or mptable
>>
>> #if defined(CONFIG_SMP) && defined(CONFIG_X86_PC) && defined(CONFIG_X86_32)
>>         if (def_to_bigsmp)
>>                 printk(KERN_WARNING "More than 8 CPUs detected and "
>>                         "CONFIG_X86_PC cannot handle it.\nUse "
>>                         "CONFIG_X86_GENERICARCH or
>> CONFIG_X86_BIGSMP.\n"); ===> here need to change "or" to "and"
>> #endif
>>
>> or just panic here? because screen scroll to pass it, and user will
>> not notice that...
>
> a panic is better but still quite rude and doesnt give a user a system
> under which he can build an even greater kernel [after having discovered
> the warning in the syslog] ;-)
>
> best would be to use as many CPUs as we can support, and skip the rest
> and boot up fine. (and print the warning prominently - the user does not
> make maximum use of available physical resources)

then  smp start AP cpu could check the apic id >=8 etc before try to
start it.in some cases

YH
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