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

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Date:	Wed, 15 Jul 2015 10:22:23 +1000
From:	Michael Ellerman <mpe@...erman.id.au>
To:	Nishanth Aravamudan <nacc@...ux.vnet.ibm.com>
Cc:	Peter Zijlstra <peterz@...radead.org>,
	linux-kernel@...r.kernel.org, Paul Mackerras <paulus@...ba.org>,
	Anton Blanchard <anton@...ba.org>,
	David Rientjes <rientjes@...gle.com>,
	linuxppc-dev@...ts.ozlabs.org
Subject: Re: [RFC,1/2] powerpc/numa: fix cpu_to_node() usage during boot

On Wed, 2015-07-08 at 16:16 -0700, Nishanth Aravamudan wrote:
> On 08.07.2015 [14:00:56 +1000], Michael Ellerman wrote:
> > On Thu, 2015-02-07 at 23:02:02 UTC, 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 
> > 
> > 
> > So it looks fairly sane, and I guess it's a bug fix.
> > 
> > But I'm a bit reluctant to put it in straight away without some time in next.
> 
> I'm fine with that -- it could use some more extensive testing,
> admittedly (I only have been able to verify the pcpu areas are being
> correctly allocated on the right node so far).
> 
> I still need to test with hotplug and things like that. Hence the RFC.
> 
> > It looks like the symptom is that the per-cpu areas are all allocated on node
> > 0, is that all that goes wrong?
> 
> Yes, that's the symptom. I cc'd a few folks to see if they could help
> indicate the performance implications of such a setup -- sorry, I should
> have been more explicit about that.

OK cool. I'm happy to put it in next if you send a non-RFC version.

cheers


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