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

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Date:	Fri, 15 Aug 2008 18:34:58 +0800 (SGT)
From:	Jeff Chua <jeff.chua.linux@...il.com>
To:	Ingo Molnar <mingo@...e.hu>
cc:	Yinghai Lu <yhlu.kernel@...il.com>,
	David Miller <davem@...emloft.net>,
	Linux Kernel <linux-kernel@...r.kernel.org>
Subject: Re: 2.6.27rc1 cannot boot more than 8CPUs



On Thu, Aug 14, 2008 at 5:07 PM, Ingo Molnar <mingo@...e.hu> wrote:
>
> * Jeff Chua <jeff.chua.linux@...il.com> wrote:
>
>> On Thu, Aug 14, 2008 at 2:33 AM, Yinghai Lu <yhlu.kernel@...il.com> 
wrote:
>>
>> >>>> > With 16 CPUs, it still hangs, but now the console is showing the
>> >>>> > errors as intended.
>> >>>> > ... but it is supposed to hang?
>>
>> > please check the attached patch. it should fix the new regression and
>> > will not hang.
>>
>> Ok, booted up and not hanged, but those messages below don't show up
>> anywhere. I've tested with CONFIG_NR_CPUS=16 and 8 as well. Just got 8
>> cpus
>>
>> More than 8 CPUs detected - skipping them.
>> Use CONFIG_X86_GENERICARCH and CONFIG_X86_BIGSMP.
>>
>> # cat /sys/devices/system/cpu/possible
>> 0-7
>>
>> CONFIG_X86_32=y
>> CONFIG_X86_PC=y
>>
>>
>> Looks like it's not going into this condition
>> +        if (def_to_bigsmp && nr_cpu_ids > 8) {
>>
>>
>> Shall this be put back so that it'll show the message?
>> -       if (def_to_bigsmp && apicid > 8) {
>> -               printk(KERN_WARNING
>> -                       "More than 8 CPUs detected - skipping them.\n"
>> -                       "Use CONFIG_X86_GENERICARCH and 
CONFIG_X86_BIGSMP.\n");
>> -       }
>
> could you post the full dmesg? And the modified patch that you've tested
> to both have 8 CPUs without bigsmp and which also shows the printk?
>
>        Ingo
>

Attached. cpu.8
    CONFIG_X86_32=y
    CONFIG_X86_PC=y
    CONFIG_X86=y
    CONFIG_NR_CPUS=8

Attached. cpu.16
    CONFIG_X86_32=y
    CONFIG_X86_PC=y
    CONFIG_X86=y
    CONFIG_NR_CPUS=16

Attached cpu.16.big
    CONFIG_X86_32=y
    CONFIG_X86=y
    CONFIG_X86_GENERICARCH=y
    CONFIG_X86_BIGSMP=y
    # CONFIG_X86_PC is not set
    CONFIG_NR_CPUS=16

Attached cpu.16.nobig (same as cpu.16 except with modifed patch)
    CONFIG_X86_32=y
    CONFIG_X86_PC=y
    CONFIG_X86=y
    CONFIG_NR_CPUS=16

Attached is the modified patch to make the warning appears. It's Yinghai's 
patch modified to just display the error and continue to boot.


Thanks,
Jeff

--- linux.16/arch/x86/kernel/smpboot.c.org	2008-08-15 18:15:37 +0800
+++ linux.16/arch/x86/kernel/smpboot.c	2008-08-15 18:13:42 +0800
@@ -999,9 +999,12 @@
  		printk(KERN_WARNING
  			"More than 8 CPUs detected - skipping them.\n"
  			"Use CONFIG_X86_GENERICARCH and CONFIG_X86_BIGSMP.\n");
-	}
-#endif
+		err = -1;
+	} else
+		err = do_boot_cpu(apicid, cpu);
+#else
  	err = do_boot_cpu(apicid, cpu);
+#endif

  	zap_low_mappings();
  	low_mappings = 0;



View attachment "cpu.8" of type "TEXT/PLAIN" (31509 bytes)

View attachment "cpu.16" of type "TEXT/PLAIN" (31509 bytes)

View attachment "cpu.16.big" of type "TEXT/PLAIN" (31519 bytes)

View attachment "cpu.16.nobig" of type "TEXT/PLAIN" (31517 bytes)