linux-kernel - Re: x86, amd: Get multi-node CPU info from NodeId MSR instead of PCI config space

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Date:	Fri, 16 Oct 2009 14:57:00 +0200
From:	Andreas Herrmann <herrmann.der.user@...glemail.com>
To:	Ingo Molnar <mingo@...e.hu>
Cc:	Thomas Gleixner <tglx@...utronix.de>,
	"H. Peter Anvin" <hpa@...or.com>, linux-kernel@...r.kernel.org,
	Yinghai Lu <yinghai@...nel.org>
Subject: Re: x86, amd: Get multi-node CPU info from NodeId MSR instead of
 PCI config space

On Fri, Oct 16, 2009 at 02:38:53PM +0200, Ingo Molnar wrote:
> 
> * Andreas Herrmann <herrmann.der.user@...glemail.com> wrote:
> 
> > Use newly introduced NodeId MSR to get NodeId and number of nodes per 
> > processor.
> 
> What will happen on CPUs that dont have this MSR and got this info from 
> the PCI config space:

No PCI config space needed as all Magny-Cours CPUs should support this
when launched.

> >  static void __cpuinit amd_fixup_dcm(struct cpuinfo_x86 *c)
> >  {
> > -#ifdef CONFIG_PCI
> > -	u32 t, cpn;
> > -	u8 n, n_id;
> >  	int cpu = smp_processor_id();
> >  
> >  	/* fixup topology information only once for a core */
> >  	if (cpu_has(c, X86_FEATURE_AMD_DCM))
> >  		return;
> >  
> > -	/* check for multi-node processor on boot cpu */
> > -	t = read_pci_config(0, 24, 3, 0xe8);
> > -	if (!(t & (1 << 29)))
> >  		return;
> >  
> >  	set_cpu_cap(c, X86_FEATURE_AMD_DCM);
> 
> are there any such CPUs?

Only Magny-Cours so far.

> I.e. we want to know the effect of this patch 
> on various models of AMD CPUs - is the change really .32 safe? Does it 
> solve any problem that makes it .32 material versus being for .33?

IMHO getting rid of the PCI config space accesses as soon as possible
is a benefit, I think.


Andreas
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