linux-kernel - Re: [PATCH 2/2] x86: Modify Kconfig to allow up to 4096 cpus

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Date:	Thu, 27 Mar 2008 08:06:42 -0700
From:	Mike Travis <travis@....com>
To:	Adrian Bunk <bunk@...nel.org>
CC:	Andrew Morton <akpm@...ux-foundation.org>, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/2] x86: Modify Kconfig to allow up to 4096 cpus

Adrian Bunk wrote:
> On Wed, Mar 26, 2008 at 09:31:22AM -0700, Mike Travis wrote:
>> Adrian Bunk wrote:
>>> On Tue, Mar 25, 2008 at 06:41:39PM -0700, Mike Travis wrote:
>>>> Increase the limit of NR_CPUS to 4096 and introduce a boolean
>>>> called "MAXSMP" which when set (e.g. "allyesconfig"), will set
>>>> NR_CPUS = 4096 and NODES_SHIFT = 9 (512).
>>>
>>> I'm not really getting the point of MAXSMP - people should simply pick 
>>> their values, and when they want the maximum "(2-4096)" and "(1-15)" 
>>> already provide this information (except that your patch hides the 
>>> latter information from the user).
>>>
>>> And with your patch, even with MAXSMP=y people could still set 
>>> NR_CPUS=7 and NODES_SHIFT=15 or whatever else they want...
>>>
>>> More interesting would be why you want it to set NODES_SHIFT to 
>>> something less than the maximum value of 15. I'm getting the fact that
>>> 2^15 > 4096 and that 15 might be nonsensical high, but this sounds more 
>>> like requiring a patch to limit the range to 9?
>> I guess the main effect is that "MAXSMP" represents what's really
>> usable for an architecture based on other factors.  The limit of
>> NODES_SHIFT = 15 is that it's represented in some places as a signed
>> 16-bit value, so 15 is the hard limit without coding changes, not
>> an architecture limit.
> 
> 
> This is the x86-specific Kconfig file that presents the x86 specific 
> limits to the users.
> 
> If NODES_SHIFT=15 is offered to the user although it's higher than the 
> current architecture limit on x86 then this is simply a bug that should 
> be fixed.
> 
> 
>> Thanks,
>> Mike
> 
> cu
> Adrian
> 

Ok, I'll modify it in the next version.  

Thanks!
Mike
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