linux-kernel - Re: [PATCH 7/8] Implement smp_processor

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Date:	Thu, 31 Aug 2006 09:04:29 -0700
From:	Jeremy Fitzhardinge <jeremy@...p.org>
To:	Ian Campbell <Ian.Campbell@...Source.com>
CC:	linux-kernel@...r.kernel.org,
	Chuck Ebbert <76306.1226@...puserve.com>,
	Zachary Amsden <zach@...are.com>,
	Jan Beulich <jbeulich@...ell.com>, Andi Kleen <ak@...e.de>,
	Andrew Morton <akpm@...l.org>,
	Chris Wright <chrisw@...s-sol.org>
Subject: Re: [PATCH 7/8] Implement smp_processor_id() with the PDA.

Ian Campbell wrote:
> This doesn't compile for me if CONFIG_SMP=n
>   

Ah, good point.

>           LD      .tmp_vmlinux1
>         arch/i386/kernel/built-in.o: In function `cpu_init':
>         (.init.text+0x1eda): undefined reference to `early_smp_processor_id'
>         arch/i386/kernel/built-in.o: In function `cpu_init':
>         (.init.text+0x1f11): undefined reference to `early_smp_processor_id'
>         
> smp_processor_id() is defined for !SMP in include/linux/smp.h, I don't
> know if it would be appropriate to add early_smp_processor_id() there
> since it seems i386 specific. asm/smp.h isn't included by linux/smp.h
> when !SMP but you could add an explicit include to common.c I suppose.
>   

I'll have a look.

I think my preferred solution would be to get rid of all the early* 
stuff, and try to arrange to have the PDA set up before C code gets 
run.  For the boot CPU, it really could be done statically (I'm not 
quite sure why the boot CPU's GDT is allocated, given that it already 
has a static one; I think this might have been a Xen-related change?).  
The secondary CPUs could have their GDT+PDA completely allocated and 
initialized in advance, making secondary CPU PDA setup just a matter of 
doing lgdt and setting %gs in head.S, even before hitting C code.

    J
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