Re: [PATCH] x86: Allow NR_CPUS=1024
From: Prarit Bhargava
Date: Sun Nov 03 2013 - 09:29:33 EST
On 11/03/2013 05:18 AM, Ingo Molnar wrote:
> * Josh Boyer <jwboyer@xxxxxxxxxx> wrote:
>> The current range for SMP configs is 2 - 512, or a full 4096 in the case
>> of MAXSMP. There are machines that have 1024 CPUs in them today and
>> configuring a kernel for that means you are forced to set MAXSMP. This
>> adds additional unnecessary overhead. While that overhead might be
>> considered tiny for large machines, it isn't necessarily so if you are
>> building a kernel that runs across a wide variety of machines. We
>> increase the range to 1024 to help with this.
>> Signed-off-by: Josh Boyer <jwboyer@xxxxxxxxxxxxxxxxx>
>> arch/x86/Kconfig | 2 +-
>> 1 file changed, 1 insertion(+), 1 deletion(-)
>> diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
>> index f67e839..d726b2d 100644
>> --- a/arch/x86/Kconfig
>> +++ b/arch/x86/Kconfig
>> @@ -825,7 +825,7 @@ config MAXSMP
>> config NR_CPUS
>> int "Maximum number of CPUs" if SMP && !MAXSMP
>> range 2 8 if SMP && X86_32 && !X86_BIGSMP
>> - range 2 512 if SMP && !MAXSMP
>> + range 2 1024 if SMP && !MAXSMP
>> default "1" if !SMP
>> default "4096" if MAXSMP
>> default "32" if SMP && (X86_NUMAQ || X86_SUMMIT || X86_BIGSMP || X86_ES7000)
> Any reason not to allow it to go up to 4096? The original concern was that
> CPUS=4096 wasn't working very well and you had to select MAXSMP
> deliberately and keep all the pieces.
> But today it's all pretty robust so I see no reason why not to allow up to
> 4096 CPUs.
Adding Russ from SGI as they are one of the consumers of a large CPU count.
I have no objections to raising this to 4096 FWIW. I think it is a good idea,
and it is long overdue.
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