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

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Message-ID: <alpine.DEB.2.11.1509301709220.4500@nanos>
Date:	Wed, 30 Sep 2015 17:11:41 +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 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.

ACPI: LAPIC (acpi_id[0x00] lapic_id[0x00] enabled)
ACPI: LAPIC (acpi_id[0x01] lapic_id[0x02] enabled)

And that's not a really large machine..

Thanks,

	tglx
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