linux-kernel - Re: [PATCH 2/6] x86: apic

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Date:	Sat, 16 Aug 2008 21:25:37 +0100 (BST)
From:	"Maciej W. Rozycki" <macro@...ux-mips.org>
To:	Arjan van de Ven <arjan@...radead.org>
cc:	Cyrill Gorcunov <gorcunov@...il.com>, mingo@...e.hu, hpa@...or.com,
	tglx@...utronix.de, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/6] x86: apic - unify lapic_resume

On Sat, 16 Aug 2008, Arjan van de Ven wrote:

> it's not like you can/want to go over 128 cpus on a 32 bit kernel
> though..

 That's a quantitative rather than a qualitative limitation though.  I can
see no reason why limiting the number of CPUs would preclude the use of
the x2APIC mode altogether -- the extra CPUs will simply be ignored and
never waken up.  And with smaller systems and a 32-bit kernel one may
still want to get the small performance gain from using the MSRs rather
than going through the TLB for example.

 Similarly there is some RAM size limitation with the 32-bit configuration
too, but that does not prevent us from using however much we can in the
32-bit mode either. ;)

  Maciej
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