linux-kernel - Re: [patch 05/14] percpu: Use a Kconfig variable to configure arch specific percpu setup

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Date:	Wed, 28 Nov 2007 17:54:55 -0800
From:	Jeremy Fitzhardinge <jeremy@...p.org>
To:	Christoph Lameter <clameter@....com>
CC:	Rusty Russell <rusty@...tcorp.com.au>, akpm@...ux-foundation.org,
	linux-kernel@...r.kernel.org, Andi Kleen <ak@...e.de>
Subject: Re: [patch 05/14] percpu: Use a Kconfig variable to configure arch
 specific percpu setup

Christoph Lameter wrote:
> The percpu areas need to be allocated in a NUMA aware fashion. Otherwise 
> you use distant memory for the most performance sensitive areas. The NUMA 
> subsystem must be so far up that these allocations can be performed in the 
> right way. And this means at least you need to know on which node each 
> processor is located. That is what the PDA is currently used for and i386 
> has no other way of doing that. I think we could use an array [NR_CPUS] 
> for this one but we want to avoid these arrays because NR_CPUS may get 
> very big.
>   

Oh, you mean there needs to be some percpu data mechanism operating in
order to do numa-aware allocations, which would be necessary to allocate
the percpu memory itself?

I can see how that would be awkward.

    J

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