Subject: Re: [BUG] rebuild_sched_domains considered dangerous
From: Peter Zijlstra <peterz@infradead.org>
To: Martin Schwidefsky <schwidefsky@de.ibm.com>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        linuxppc-dev <linuxppc-dev@lists.ozlabs.org>,
        Jesse Larrew <jlarrew@linux.vnet.ibm.com>
In-Reply-To: <20110309143152.3cc6c191@mschwide.boeblingen.de.ibm.com>
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Date: Wed, 09 Mar 2011 14:33:56 +0100
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On Wed, 2011-03-09 at 14:31 +0100, Martin Schwidefsky wrote:
> > But if you don't also update the cpu->node memory mappings (which I
> > think it near impossible) what good is it to change the scheduler
> > topology?
> 
> The memory for the different LPARs is striped over all nodes (or books as we
> call them). We heavily rely on the large shared cache between the books to hide
> the different memory access latencies. 

Right, so effectively you don't have NUMA due to that striping. So why
then change the CPU topology? Simply create a topology without NUMA and
keep it static, that accurately reflects the memory topology.


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