linux-kernel - Re: [PATCH v3] x86/cpu: Allow higher NR

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Date:	Thu, 7 Nov 2013 10:15:55 +0100
From:	Ingo Molnar <mingo@...nel.org>
To:	Josh Boyer <jwboyer@...hat.com>
Cc:	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	"H. Peter Anvin" <hpa@...or.com>, prarit@...hat.com,
	x86@...nel.org, linux-kernel@...r.kernel.org,
	Russ Anderson <rja@....com>
Subject: Re: [PATCH v3] x86/cpu: Allow higher NR_CPUS values


* Josh Boyer <jwboyer@...hat.com> wrote:

> The current range for SMP configs is 2 - 512 CPUs, 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.
> 
> To cover the range of more common machines today, we allow NR_CPUS to be
> up to 4096 when CPUMASK_OFFSTACK is enabled.  Relatedly, we no longer make
> that option depend on DEBUG_PER_CPU_MASKS.

> index b3c8be0..50b47cd 100644
> --- a/lib/Kconfig
> +++ b/lib/Kconfig
> @@ -342,7 +342,8 @@ config CHECK_SIGNATURE
>  	bool
>  
>  config CPUMASK_OFFSTACK
> -	bool "Force CPU masks off stack" if DEBUG_PER_CPU_MAPS
> +	bool "Force CPU masks off stack"
> +	depends on SMP
>  	help
>  	  Use dynamic allocation for cpumask_var_t, instead of putting
>  	  them on the stack.  This is a bit more expensive, but avoids

So this chunk really doesn't belong into the patch - it should be a 
separate patch.

Also, because I already applied the patch (sans the unrelated chunk) 
please only send this single change against tip:master.

Thanks,

	Ingo
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