linux-kernel - Re: [PATCHv3 2/2] powerpc: implement arch_scale_smt

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Date:	Fri, 29 Jan 2010 12:34:47 -0600
From:	Joel Schopp <jschopp@...tin.ibm.com>
To:	Peter Zijlstra <peterz@...radead.org>
CC:	Benjamin Herrenschmidt <benh@...nel.crashing.org>, ego@...ibm.com,
	linuxppc-dev@...ts.ozlabs.org, Ingo Molnar <mingo@...e.hu>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCHv3 2/2] powerpc: implement arch_scale_smt_power for Power7


> That said, I'm still not entirely convinced I like this usage of
> cpupower, its supposed to be a normalization scale for load-balancing,
> not a placement hook.
>   
Even if you do a placement hook you'll need to address it in the load 
balancing as well.  Consider a single 4 thread SMT core with 4 running 
tasks.  If 2 of them exit the remaining 2 will need to be load balanced 
within the core in a way that takes into account the dynamic nature of 
the thread power.  This patch does that.
> I'd be much happier with a SD_GROUP_ORDER or something like that, that
> works together with SD_PREFER_SIBLING to pack active tasks to cpus in
> ascending group order.
>
>   
I don't see this load-balancing patch as mutually exclusive with a patch 
to fix placement.  But even if it is a mutually exclusive solution there 
is no reason we can't fix things now with this patch and then later take 
it out when it's fixed another way.  This patch series is 
straightforward, non-intrusive, and without it the scheduler is broken 
on this processor. 
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