linux-kernel - Re: [patch 2/4] x86: Fix build breakage when PCI is define and PARAVIRT is not

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Date:	Fri, 21 Mar 2008 19:19:51 -0700
From:	Jeremy Fitzhardinge <jeremy@...p.org>
To:	Ravikiran G Thirumalai <kiran@...lex86.org>
CC:	Andrew Morton <akpm@...ux-foundation.org>,
	Ingo Molnar <mingo@...e.hu>, linux-kernel@...r.kernel.org,
	Glauber de Oliveira Costa <gcosta@...hat.com>,
	Andi Kleen <ak@...e.de>, shai@...lex86.org
Subject: Re: [patch 2/4] x86: Fix build breakage when PCI is define and PARAVIRT
 is not

Ravikiran G Thirumalai wrote:
> Well, vSMPowered bits in the kernel serves two objectives:
> a) Internode cacheline size
> b) paravirt irq ops
>
> A vSMPowered machine can boot without either, but both affect performance.
> Both these bits are not interdependent.  The paravirt ops
> need the PARAVIRT infrastructure and that is all that is needed.
> The internode cacheline size needs a compile time definition that's all.
> CONFIG_X86_VSMP chooses both.  However, there is no reason to have paravirt
> irq ops depend on the Internode cacheline size.  More so since pv ops
> has the capability to detect the system type dynamically and using
> appropriate pv ops.
>   

So are you saying that X86_VSMP is just to select the internode 
cacheline size, and is independent of the pvops side of things?

If so, I think it would be worth adding a separate config variable so 
that you have the following:

VSMP (depends on PCI) - master selector for all vsmp-related code; 
enables vsmp detection code
VSMP && PARAVIRT - installs paravirt irq ops on a vsmp system
VSMP_CACHELINE_SIZE (depends on VSMP) - selects internode cacheline size

that way vsmp_64.o can just depend on VSMP, and at the very least 
contains the query code, and the other features are independently 
selectable.

    J
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