linux-kernel - Re: [PATCH RFC] x86: Reduce MAX_LOCAL_APIC and MAX_IO

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Date:	Wed, 30 Sep 2015 19:43:23 +0200 (CEST)
From:	Thomas Gleixner <tglx@...utronix.de>
To:	Denys Vlasenko <dvlasenk@...hat.com>
cc:	Ingo Molnar <mingo@...nel.org>,
	Jiang Liu <jiang.liu@...ux.intel.com>,
	Len Brown <len.brown@...el.com>, x86@...nel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH RFC] x86: Reduce MAX_LOCAL_APIC and MAX_IO_APICS

On Wed, 30 Sep 2015, Denys Vlasenko wrote:
> On 09/30/2015 05:11 PM, Thomas Gleixner wrote:
> > On Fri, 25 Sep 2015, Denys Vlasenko wrote:
> >>  
> >> +config MAX_LAPIC_ID
> >> +	int "Maximum APIC ID"
> >> +	range 8 32768
> >> +	default "8"
> >> +	---help---
> >> +	  Use this option to set maximum allowed Local APIC ID higher than
> >> +	  maximum number of CPUs. This may be necessary for machines
> >> +	  with large number of processor sockets and non-contiguous
> >> +	  LAPIC numbering.
> >> +	  This setting will be automatically rounded up, if necessary.
> > 
> > This is wrong. If you would limit the APIC IDs then you really break
> > stuff. You can only limit the number of APICs.
> 
> This CONFIG setting allows to _increase_ max APIC ID.

NO. This is crap. I don't want to tweak a gazillion of knobs just to
build a kernel with CONFIG_NR_CPUS=8. Really not.

If you really want to make that space saving, then make it a runtime
allocation.
 
Thanks,

	tglx
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