Re: 2.6.27rc1 cannot boot more than 8CPUs

["Yinghai Lu" <yhlu.kernel@gmail.com>]

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On Mon, Aug 11, 2008 at 1:12 PM, Yinghai Lu <yhlu.kernel@gmail.com> wrote:
> On Mon, Aug 11, 2008 at 1:08 PM, Ingo Molnar <mingo@elte.hu> wrote:
>>
>> * Yinghai Lu <yhlu.kernel@gmail.com> wrote:
>>
>>> On Mon, Aug 11, 2008 at 12:59 PM, Ingo Molnar <mingo@elte.hu> wrote:
>>> >
>>> > * Jeff Chua <jeff.chua.linux@gmail.com> wrote:
>>> >
>>> >> On Wed, Aug 6, 2008 at 2:42 PM, Jeff Chua <jeff.chua.linux@gmail.com> wrote:
>>> >> > On Wed, Aug 6, 2008 at 2:01 PM, Linus Torvalds
>>> >> > <torvalds@linux-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

please check attach patches..

YH

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[PATCH] x86: move def_to_bigsmp check later

and skil the apicid id > 8

Signed-off-by: Yinghai Lu <yhlu.kernel@gmail.com>

diff --git a/arch/x86/kernel/setup.c b/arch/x86/kernel/setup.c
index 6917779..59f07e1 100644
--- a/arch/x86/kernel/setup.c
+++ b/arch/x86/kernel/setup.c
@@ -863,12 +863,6 @@ void __init setup_arch(char **cmdline_p)
 	init_apic_mappings();
 	ioapic_init_mappings();
 
-#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");
-#endif
 	kvm_guest_init();
 
 	e820_reserve_resources();
diff --git a/arch/x86/kernel/smpboot.c b/arch/x86/kernel/smpboot.c
index 21821f3..ce4ee3e 100644
--- a/arch/x86/kernel/smpboot.c
+++ b/arch/x86/kernel/smpboot.c
@@ -987,7 +987,17 @@ int __cpuinit native_cpu_up(unsigned int cpu)
 	flush_tlb_all();
 	low_mappings = 1;
 
+#ifdef CONFIG_X86_PC
+        if (def_to_bigsmp && apicid > 8) {
+                printk(KERN_WARNING "More than 8 CPUs detected and "
+                        "CONFIG_X86_PC cannot handle it.\nUse "
+                        "CONFIG_X86_GENERICARCH and CONFIG_X86_BIGSMP.\n");
+		err = -1;
+	} else
+		err = do_boot_cpu(apicid, cpu);
+#else
 	err = do_boot_cpu(apicid, cpu);
+#endif
 
 	zap_low_mappings();
 	low_mappings = 0;