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

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Date:	Thu, 7 Nov 2013 08:51:08 -0500
From:	Josh Boyer <jwboyer@...hat.com>
To:	Ingo Molnar <mingo@...nel.org>
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

On Thu, Nov 07, 2013 at 10:15:55AM +0100, Ingo Molnar wrote:
> 
> * 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.

I missed that you removed that chunk, my mistake.  I'll send a follow up
as you suggest.

josh
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