linux-kernel - Re: [RFC PATCH 1/2] powerpc/numa: fix cpu_to

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Date:	Wed, 15 Jul 2015 15:43:51 -0700
From:	Nishanth Aravamudan <nacc@...ux.vnet.ibm.com>
To:	Tejun Heo <tj@...nel.org>
Cc:	Michael Ellerman <mpe@...erman.id.au>,
	David Rientjes <rientjes@...gle.com>,
	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	Paul Mackerras <paulus@...ba.org>,
	Anton Blanchard <anton@...ba.org>,
	Peter Zijlstra <peterz@...radead.org>,
	linuxppc-dev@...ts.ozlabs.org, linux-kernel@...r.kernel.org
Subject: Re: [RFC PATCH 1/2] powerpc/numa: fix cpu_to_node() usage during boot

On 15.07.2015 [16:35:16 -0400], Tejun Heo wrote:
> Hello,
> 
> On Thu, Jul 02, 2015 at 04:02:02PM -0700, Nishanth Aravamudan wrote:
> > we currently emit at boot:
> > 
> > [    0.000000] pcpu-alloc: [0] 0 1 2 3 [0] 4 5 6 7 
> > 
> > After this commit, we correctly emit:
> > 
> > [    0.000000] pcpu-alloc: [0] 0 1 2 3 [1] 4 5 6 7 
> 
> JFYI, the numbers in the brackets aren't NUMA node numbers but percpu
> allocation group numbers and they're not split according to nodes but
> percpu allocation units.  In both cases, there are two units each
> serving 0-3 and 4-7.  In the above case, because it wasn't being fed
> the correct NUMA information, both got assigned to the same group.  In
> the latter, they got assigned to different ones but even then if the
> group numbers match NUMA node numbers, that's just a coincidence.

Ok, thank you for clarifying! From a correctness perspective, even if
the numbers don't match NUMA nodes, should we expect the grouping to be
split along NUMA topology?

-Nish

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