linux-kernel - Re: [PATCH 4/4] x86, amd: Support L3 Cache Partitioning on AMD family 0x15 CPUs

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Date:	Thu, 27 Jan 2011 13:47:56 +0100
From:	Ingo Molnar <mingo@...e.hu>
To:	Hans Rosenfeld <hans.rosenfeld@....com>
Cc:	"hpa@...or.com" <hpa@...or.com>,
	"tglx@...utronix.de" <tglx@...utronix.de>,
	"Herrmann3, Andreas" <Andreas.Herrmann3@....com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"x86@...nel.org" <x86@...nel.org>
Subject: Re: [PATCH 4/4] x86, amd: Support L3 Cache Partitioning on AMD
 family 0x15 CPUs


* Hans Rosenfeld <hans.rosenfeld@....com> wrote:

> On Wed, Jan 26, 2011 at 03:56:08PM -0500, Ingo Molnar wrote:
> > * Hans Rosenfeld <hans.rosenfeld@....com> wrote:
> > > +#ifdef CONFIG_SMP
> > > +int amd_get_subcaches(int cpu)
> > 
> > Well, sprinkling it with CONFIG_SMP is pretty ugly. Also, there's no fundamental 
> > reason why this shouldnt work with UP. Yes, it makes most sense on SMP but such code 
> > should be SMP-invariant.
> 
> True, it is pretty ugly. And while the feature is pretty useless for UP,
> it would still work for compute_unit_id 0 in that case.
> 
> The problem is that cpuinfo_x86.compute_unit_id etc. don't exist unless
> CONFIG_SMP is enabled. I don't think there is any reason why this should
> be that way, but changing this just for this particular L3 feature seems
> too intrusive. Do you really want me to do that?

All the CONFIG_X86_HT #ifdefs in arch/x86/kernel/cpu/amd.c look pretty ugly too - 
and it's not really a properly modularized solution.

We generally want to unify the SMP and UP kernels as much as possible. 'CONFIG_SMP' 
is not really a property of the hardware, it's a property of the software.

If some topology information should be excluded then it can already be done by 
turning off CONFIG_CPU_SUP_AMD under CONFIG_EXPERT.

Thanks,

	Ingo
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